Glossary of Automotive Terms – R

Letter R – Dictionary of Automotive Terms

  1. Letter designation for tires to indicate that they are Radial as in P185R13 tire.
  2. Reverse.
  3. A letter on a fuel gauge indicating low fuel; when first illuminated it indicates that there is approximately five litres left in reserve.
  4. Symbol for resistance
(trichloromonofluoromethane) Low pressure, synthetic chemical refrigerant which is also used as a cleaning fluid.
(dichlorodifluoromethane) Popular refrigerant known as Freon 12.
(monochlorodifluoromethane) Low temperature refrigerant with boiling point of -40.5°C at atmospheric pressure.
(trichlorotrifluoroethane) Synthetic chemical refrigerant which is nontoxic and nonflammable.
(ethyl chloride) Toxic refrigerant now seldom used.
(ethane) Low temperature application refrigerant.
(propane) Low temperature application refrigerant.
Refrigerant which is an azeotropic mixture of R-12 andR-152a.
Refrigerant which is azeotropic mixture of R-22 and R-115.
Refrigerant which is azeotropic mixture of R-23 and R-13.
Refrigerant which is azeotropic mixture of R-32 and R-115.
(butane) Low-temperature application refrigerant; also used as a fuel.
(methyl formate) Low pressure refrigerant.
(ammonia) Popular refrigerant for industrial refrigerating systems; also a popular absorption system refrigerant.
Abbreviation for Rear-wheel Anti-lock Brake System (Ford)
Abbreviation for the Royal Automobile Club.
Bearing RaceBearing Race

  1. The inner or outer ring that provides a contact surface for the balls or rollers in a bearing.
  2. A competition (usually based on speed) between two vehicles.
  3. To run an engine at high speed when not in gear.
Race cam
A type of camshaft for race car engines which increases lift of valve, speed of valve opening and closing, length of time valve is held open, etc. Also called Full cam, Three-quarter cam, or Semi-race cam, depending upon design.
Race camshaft
A camshaft, other than stock, designed to improve engine performance by altering Cam profile. Provides increased lift, faster opening and closing, earlier opening and later closing, etc. Race camshafts are available as semi-race or street grind, Three-quarter race camshaft or full race. Grinds in between these general categories are also available.

Racing Green
Racing harness
Racing start
A start on a normal street, e.g., at traffic lights, using excessive throttle resulting in wheelspin and screeching tires.
  1. A long, toothed bar.
  2. Removable wood or metal wall sections attachable to flatbed trailers to make sides for confining loads.
Rack and pinion
Rack and pinion gearbox
Rack and pinion gearboxRack and pinion gearbox

A type of Steering system with a Pinion gear on the end of the Steering shaft. The pinion engages a long rack (a bar with a row of teeth cut along one edge). When the steering wheel is turned, the pinion turns and moves the rack to the left or right. This movement is carried through Tie rods to the steering arms at the wheels.

Rack and pinion steering
Rack and pinion steeringRack and pinion steering

The pinion gear rotates with the steering shaft, moving the rack from side to side. Several full turns of the pinion are required to shift the rack from lock to lock. Because there are so few parts in the steering linkage, rack and pinion is a very precise and responsive steering system and is often used in sports cars.

Rack-and-pinion steering
Racked Cross Stringers
The output from a PDS program describing the maximum load carrying capacity and deflection of a pallet where the rack frame supports the pallet only at the ends of the stringers or stringer boards.
Rack galvanizing
A galvanizing method for objects which can be placed on a rack.
Abbreviation for radiator.
Abbreviation for radiator temperature switch
Radar detector
A device which will sense the presence of a radar device which law enforcement officers might be using to spot speeders.
Radial bearing
A bearing designed to absorb the radial forces acting on a pump. Compare Thrust bearing
Radial clearance
Radial commutator
Electrical contact surface on a rotor which is perpendicular or at right angles to the shaft center line.
Radial compressor
A compressor with pistons radiating out from the centerline of the compressor. The Harrison (Frigidaire) is a typical example.
Radial cooling fins
Brake drum cooling fins that are parallel to the centerline of the axle.
Radial cracking
Cracking of sidewall rubber running perpendicular to the tire beads. May result from underinflation or exposure to ozone.
Radial discharge nozzle
Booster venturi with four spokes or arms which carry fuel to the outer circumference of the booster before discharging it from tiny holes in the ends of the spokes. Used only on the Corvair Model H carburetor.
Radial engine
Radial EngineRadial Engine

An internal combustion engine with a number of cylinders arranged in a circle around the crankshaft center line. As the crankshaft turns, the pistons are in various stages of the strokes (i.e., intake, exhaust, compression, power). A design often used for aircraft engines.

Radial-flow pump
Radial-flow pumpRadial-flow pump

An end-suction centrifugal pump with the liquid flowing perpendicular to the pump shaft. The liquid enters at the center of the impeller and is directed out along the impeller blades in a direction at right angles to the pump shaft.

Radial load
A load perpendicularly applied to the axis of rotation.
Radial play
A bearing clearance in the radial direction.
Radial ply
Radial plyRadial ply

The ply or plies used in tire in which the cords run at right angles to the bead and parallel to the tire radius.

Radial ply tire
A type of tire construction in which sidewall structural plies run radially out towards the tread instead of criss-cross diagonally. With their thinner, more flexible sidewalls, radial tires have lower rolling resistance than cross-ply tires (yielding better fuel consumption) as well as giving longer tread life. They can accommodate the use of low inflation pressures without overheating, due to their flexible sidewalls, but are sometimes more prone to sidewall damage when operating in rocky or stony conditions. Because radial tires invariably also have a braced tread area of great dimensional stability, they ‘track-lay’ the tread (like a bulldozer), do not suffer from ‘tread shuffle’ and so achieve more traction in limiting off-road conditions.
Radial runout
  1. A tire assembly that does not form a true circle; the radii of the circle are not equal. Most usual causes are bent wheel (out of round) or tire not mounted properly (beads not seated). This is one of the main causes of vehicle vibration.
  2. A variation in the diameter of a brake disc, wheel, or tire from a specified amount.
Radial shaft seal
A typical seal design used to prevent leaks between stationary parts and rotating shafts and to exclude foreign matter. A lip seal, typically of neoprene, is held in a metal retainer and applies a sealing pressure to a rotating shaft, the pressure being provided by an annular garter spring winch surrounds the sealing lip; radial shaft seals are used wherever a shaft penetrates a casing, such as on crankshafts, camshafts, water pump shafts, etc.
Radial tire
Radial tireRadial tire

A type of tire construction which has the main carcass plies or cords which run at right angles to the bead and parallel to the radius. By itself, this construction is very weak because when the Bias angle is smaller, the structure is stiff. However, the radial tire has a very large Bias angle. In order to strengthen the tire, a belt surrounds the circumference. This belt is made of low-angle plies (usually about 15 degrees). In this way, the tread area is stiff and the sidewalls are flexible. In this way the sidewalls can act independently of each other. In a P185/80R13 tire, R indicates a radial tire.

Radiant barrier
A thin, reflective foil sheet that exhibits low radiant energy transmission and under certain conditions can block radiant heat transfer; installed in attics to reduce heat flow through a roof assembly into the living space.
Radiant drier
Radiant energy
Energy that transmits away from its source in all directions.
Radiant heating
Heating system in which warm or hot surfaces are used to radiate heat into the space to be conditioned.
  1. The transfer of heat from one object to another when the hotter object sends out invisible rays or waves that upon striking the colder object, cause it to vibrate and thus heat.
  2. The process by which energy (such as heat) is emitted by one body, as particles or waves, transmitted through an intervening medium or space (like air), and absorbed by another body. Also refers to the energy transferred by this process
  3. The transfer of heat through matter or space by means of electromagnetic waves.
Radiation shield
A separate panel or panels interposed between surfaces and jackets to reduce heat losses through radiation.
Radiative forcing
A change in average net radiation at the top of the troposphere (known as the tropopause) because of a change in either incoming solar or exiting infrared radiation. A positive radiative forcing tends on average to warm the earth’s surface; a negative radiative forcing on average tends to cool the earth’s surface. Greenhouse gases, when emitted into the atmosphere, trap infrared energy radiated from the earth’s surface and therefore tend to produce positive radiative forcing.

Radiatively active gases
Gases that absorb incoming solar radiation or outgoing infrared radiation, affecting the vertical temperature profile of the atmosphere.


A device that cools the liquid in the cooling system by allowing it to circulate through a series of water channels, which are exposed to air Ducts.

Radiator cap
Pressure capPressure cap

  1. A Pressure cap at the top of the radiator.
  2. A high pressure cap used in radiators to allow operation at high temperature. Higher pressure raises the boiling point of the coolant.
Radiator drain cock
Radiator drain cockRadiator drain cock

A radiator tap; unlike the Radiator drain plug, tools are not required to drain the coolant from a radiator with a drain cock.

Radiator drain plug
A threaded closure plug located at the underside of a radiator used to drain the coolant; usually equipped with a hex or Allen head.
Radiator fan
Two types are used on automobiles a crankshaft-driven fan connected by a temperature-sensitive viscous coupling, or a fan driven by an electric motor.
Radiator fan motor
An electrically operated motor responsible for driving the radiator fan. An electric motor allows much more freedom in radiator location and engine bay design and permits aftercooling of the engine with the engine switched off most engines mounted crosswise at the front (as on most front-wheel-drive subcompacts) use electric radiator fans which also lead to reduced power losses, since the vehicle’s engine is not also required to drive the radiator fan also. The problem with them, however, is that even with the engine off, the fan may start up unexpectedly for the person inspecting the engine bay.
Radiator fill hole
An opening at the top of the radiator through which new water and coolant can be added when the engine and radiator is cool. In modern vehicles, an overflow reservoir is the location for topping off the radiator fluid since opening a hot radiator cap can be dangerous. The Pressure cap seals the fill hole.
Radiator grille
The grating that admits cooling air to the radiator.
Radiator grille surround
The sheet metal panel for mounting the radiator grille; often combined with the front apron to form a single front panel.
Radiator guard
Radiator hose
The rubber pipe connecting the radiator to the cylinder block.
Radiator hose shark tooth pliers
A special automotive tool for removing and installing radiator and heater hoses; round and toothed jaws securely grip the hose while the handles provide leverage to twist the hose free.
Radiator overflow tank
Radiator overflow tankRadiator overflow tank

A small bottle that acts as a reservoir for liquid expelled from the cooling system through the Overflow pipe and returns the liquid to the system when it cools down. A special radiator Pressure cap is also part of the kit. It is also called a Closed Cooling System when it is part of the Original equipment.

Radiator pressure cap
Radiator shell
Radiator ShellRadiator shell

A metal or plastic enclosure which surrounds the outside perimeter of the radiator and mounts to the frame of the vehicle. In modern motorcycles, it is usually chromed.

Radiator support panel
A panel located behind the radiator grille surround which provides a mounting for the radiator and connects the mudguard skirts at their front edge.
Radiator tank
A reservoir containing the coolant in a radiator. Early units were made from sheet metal, typically brass or aluminum. Newer versions used advanced polymer technology and injection molding processes have made it possible to produce radiator tanks from thermoplastics. Since all modern cars use forced circulation systems, there is no need for a vertical flow through the radiator. Thus most radiators are mounted horizontally. Also called Radiator Overflow Tank
Radii adapter
A mounting device that is used to center a drum or rotor on the arbor of a lathe. A radii adapter centers the drum or rotor through contact with the bearing races.
A device which receives radio signals (either AM, FM, or both) and plays the sound through the speakers. Automobile radios began to appear in vehicles in 1928. Even in the mid-1960s, many cars came without radios.

Radio/cassette deck
(r/c) A combined radio and tape deck.
Radio choke
An electric coil used to prevent static in the radio caused by opening and closing of the contact points in the instrument voltage regulator.
Radio data System
(RDS) A system which interrupts a radio broadcast with the latest information on e.g., traffic problems.
Radio frequency interference
(RFI) interference generated by the ignition system and other electrical apparatus; counteracted by suppressors.
A photograph obtained by passing X-rays or gamma rays through the object to be photographed and recording the variations in density on a photographic film.
Radius arm
An additional suspension link in a beam axle layout providing fore-and-aft location of the axle.
Radius rod
An additional suspension link in a beam axle layout providing fore-and-aft location of the axle.
Radius rods
Rods or arms which are part of the suspension, usually a live rear axle. They are attached to the axle and pivoted on the frame. They are used to keep the axle at right angles to the frame (i.e., prevent lateral movement) and yet permit an up and down motion. On some cars like the Triumph Spitfire, they are used to help locate the Swing axles.
Radius seat
A spherical seat that provides positive centering of the wheel bolt head in the wheel.
A naturally occurring radioactive gas found in the United States in nearly all types of soil, rock, and water. It can migrate into most buildings. Studies have linked high concentrations of radon to lung cancer.
Abbreviation for Reactivity Adjustment Factor


Colloquial term for convertible.
Abbreviation for Nederlandse vereniging de Rijwiel-en-Automobiel Indusrie (Netherlands).
  1. A Dragster built around a relatively long pipe frame. The only body panels used are around the Driver’s cockpit area.
  2. A common pressure accumulator.
Rail console
Rail job
A vehicle that has been transformed into a dragster built around a long pipe frame with minimal body panels.
Rail Joint
Railroad locomotive
Self-propelled vehicle that runs on rails and is used for moving railroad cars.
A vehicle brand of which the 1925-1948 models, with required application, are classic cars.
Railway Container
A cargo container that can be loaded or stacked on a railroad flat car.

Rain grooves
Channels cut into a road’s surface to help water run off the road during a rainstorm
A model of automobile manufactured by Buick Division of General Motors from 2004-07
The action of beating a rounded shape out of a flat panel by starting in the center and working outward in a spiral to the edge; the metal is shrunk around the edge but remains about the same in the center.
  1. The angle at which a rod is attached.
  2. The fore-and-aft inclination from the vertical.
A vehicle which has the Ground clearance or body altered so that either the front or rear of the vehicle is increased or lowered, thus giving the vehicle a tilted appearance.
Rake the leaves
Trucker slang for the last vehicle in a string as in ‘Looks like I get to rake the leaves tonight.’
Abbreviation for Random Access Memory — memory that serves as a temporary storage place for data from the sensors.
Ram air
  1. In a ram air system, carburetors get fresh air to be mixed with the gasoline via forward facing ducts. The idea is that as the vehicle moves faster, more air is forced or rammed into the carburetors resulting in improved performance.
  2. A term referring to the air forced through the condenser coils by vehicle movement or fan action.
Ram induction
Using the forward Momentum of vehicle to scoop air and force it into carburetor via a suitable passageway.
Ram intake manifold
An intake manifold that has very long passageways that at certain speeds aid the entrance of fuel mixture into the cylinders.
  1. Equipment used to support a vehicle’s front or rear for underbody work.
  2. A device used to raise a vehicle in the air.
Ramp angle
A measure of vehicle under-belly clearance or the ability to drive over a sharp ridge or ramp without touching the underside of the vehicle on the obstacle. The ramp angle is the angle measured from the lowest part of the chassis at mid-wheelbase down to the periphery of front and rear wheels. Obviously a short wheelbase vehicle with large wheels will have the smallest ramp angle and best under-belly clearance.
Ramp breakover angle
Ramp-over angle
An indication of how high a hump the vehicle can negotiate without scraping the undercarriage or becoming high-centered; that is, stuck with the center of the vehicle on the hump and the wheels in the air.
Ram pressure
The pressure generated by the deflection of the fluid flow due to the curvature of the stator blades, resulting in a momentum acting on the turbine.
Ram tube
A tube of a specific length and shape in the intake manifold that promotes performance at certain engine speeds by ramming air into the cylinders.
A two-door vehicle produced by Ford which had an automobile front end and a truck-like cargo bed behind the front compartment.
Abbreviation for Research & Development.
Random access memory
(RAM) A type of volatile memory that is used to store information for either short or long term usage. This type of memory can be written to. If energy is removed from the RAM device, the contents in memory are destroyed.

A long bicycle touring ride of 160 to 1200 kilometres made up of several controls (checkpoints).
A male long-distance cyclist.

Randonneur 5000
One of the most prestigious awards a Randonneur can earn. To be one of the recipients, a randonneur must do a full series of 200, 300, 400, 600, and 1000km Brevets, a Paris-Brest-Paris randonneur event, a Flèche team ride, and the remaining distances ridden on sanctioned brevets for a total of 5000 kilometres. The qualifying events must all be completed within a four-year period.
Long distance bicycle riding within a specified length of time. First developed in France in 1891 a few years before the Tour de France which later spun off from randonneuring. It is not considered a race but a ride. Everyone who completes the ride within the time limit is awarded the same medal regardless of how quickly he/she rides the distance.
Randonneurs Mondiaux
An umbrella organization of national randonneuring groups. Its primary functions are to organize foreign (i.e., France, Spain, United Kingdom, Holland, Belgium, Australia, Denmark, Sweden, Norway, Finland, Austria, Germany, Russia, South Africa, Canada, and the United States) participation in Paris-Brest-Paris and other 1200-kilometre Brevets, encourage the exchange of information of interest to randonneurs, and reward clubs’ and individuals’ participation in long-distance randonnées with various medals and trophies.
  1. A female long-distance cyclist.
  2. A bicycle specifically designed for randonneuring.
Pressure or temperature settings of a control; change within limits.

The transfer gearbox lever

Range gearbox
Range gearing
Range reserve
Range Rover
Range RoverClick image for books on
Range Rover

A model of SUV manufactured in England

Range transmission

Rankine cycle
The thermodynamic cycle that is an ideal standard for comparing performance of heat-engines, steam power plants, steam turbines, and heat pump systems that use a condensable vapor as the working fluid. Efficiency is measured as work done divided by sensible heat supplied.
Rankine cycle engine
The Rankine cycle system uses a liquid that evaporates when heated and expands to produce work, such as turning a turbine, which when connected to a generator, produces electricity. The exhaust vapor expelled from the turbine condenses and the liquid is pumped back to the boiler to repeat the cycle. The working fluid most commonly used is water, though other liquids can also be used. Rankine cycle design is used by most commercial electric power plants. The traditional steam locomotive is also a common form of the Rankine cycle engine. The Rankine engine itself can be either a piston engine or a turbine.
Rankine scale
Name given the absolute (Fahrenheit) scale. Zero (0°R) on this scale is -460°F
Abbreviation for Retained Access Power
Rapid Transit

  1. A tool like a file with coarse teeth used to prepare a tire for Section repair and for Buffing prior to Retreading.
  2. The action of using a rasp tool.
  1. A feature of a special wrench which allows you to turn the handle in one direction to tighten a nut or bolt, but turning it in the opposite direction does nothing but position the handle back where you started and leaves the wrench on the nut or bolt. Likewise you could set the wrench to loosen a nut or bolt.
  2. A drive handle with ratchet mechanism, usually called a Socket wrench.
  3. A toothed Rack or wheel which is engaged by a lever to permit motion in only one direction.
Ratchet adapter
A device which converts a torque wrench or drive handle without a ratchet mechanism into a reversible ratchet tool.
Ratchet handle
A Ratchet tool.
Ratchet jaw
Trucker slang for a non-stop talker as in ‘He sure was a ratchet jaw.’
Ratchet screwdriver
A screwdriver with a ratchet mechanism.
Rated capacity
The quantity of electricity which can be drawn from a fully charged battery for 20 hours by a constant discharging current until cutoff voltage of 1.75 volts per cell is reached.

Rated horsepower
Rated power
  1. The power output of an engine as horsepower or kilowatt.
  2. The value stated on the generator nameplate. It is the power available at the output terminals of a component or piece of equipment that is operated in compliance with the manufacturer’s performance specifications.
Rated pressure
A nominal pressure rating applied to vehicle parts.
Rated voltage
The voltage given for electrical equipment or devices which refers to specified operating conditions.
Rate manual
Rate spring
Rate suspension
Rat Hole Service
Drilling rigs.
A fixed relationship between things in number, quantity or degree. For example, if the fuel mixture contains one part of gas for fifteen parts of air, the ratio would be 15 to 1.

Ratio Adapter Controller Module
An industrial reorganization primarily aimed at a more cost-effective and time-saving production process.
Ratio steering
Rat-tail file
A Round file.
Rattle spring
The type of bicycle pedals that have thin metal plates with jagged edges running parallel on each side of the pedal spindle.
RAVE valve
A device used on two-stroke engines which automatically alters or varies the exhaust port size. It stands for Rotax adjustable variable exhaust.
Ravigneaux planetary gear set
A system which is composed of two sun gears of different diameters, one internal gear, and several planet pinions.
Raw exhaust gas
The exhaust gas upstream of any emission control device, e.g., before it passes through a catalytic converter.
Raw rubber
Natural rubber that has not been vulcanized.
Rayleigh frequency distribution
A mathematical representation of the frequency or ratio that specific wind speeds occur within a specified time interval.
A vehicle brand of which the 1925-1948 models with required application are classic cars.
A synthetic fiber.
Ray Tube


Abbreviation for reformulated gasoline blendstock for oxygenate blending

Abbreviation for Respirable Combustible Dust
Abbreviation for Refuse-derived fuel
Abbreviation for Radio data system.
Abbreviation for Roadster.
RDXClick image for books on

An automobile manufactured by Acura

The distance from the sealing washer of a spark plug to the end of the thread.
  1. That part of the impedance of an alternating current circuit due to capacitance or inductance or both.
  2. A phenomenon associated with AC power characterized by the existence of a time difference between voltage and current variations.
Reactionary type valve
A unit which responds to fluid displacement and pressure, or mechanical linkage movement and force, to modulate pressure in a brake cylinder or chamber.
Reaction distance
The time needed to respond to a situation, translated into the distance required for this, depending on the speed of travel; braking distance plus reaction distance equals the stopping distance.

Reaction injection molding
(RIM) A processing technique for the production of large foamed automotive components, based on the simultaneous injection of the liquid components and the chemical reaction in the mold. Compare Polymerization. In some cases, the components are mixed immediately before being injected into the mold. The term RIM is also applied to refer to the plastic material produced by this technique, e.g., ‘RIM-PUR.’

Reaction member

Reaction rate
A measure of the speed of a chemical reaction. The reaction rate depends on the rate constant, the number of reactants involved in the reaction and their concentration. For reactions that are otherwise slow, a catalyst is employed to increase the reaction rate.
Reaction System
Reaction Time
To restore the tackiness of a completely dried adhesive. Reactivated adhesives are useful in that the adhering surfaces may be coated with adhesive and the surfaces mated again after short term exposure. Reactivated bonds set almost immediately

Reactivation Solvent
To restore the surface tackiness in a dry adhesive film with a suitable solvent.
Reactive power
  1. For sinusoidal quantities in a two-wire circuit; the product of the voltage, the current, and the sine of the phase angle between them. In a polyphase circuit; the sum of the reactive powers of the phases.
  2. The portion of electricity that establishes and sustains the electric and magnetic fields of alternating-current equipment. Reactive power must be supplied to most types of magnetic equipment, such as motors and transformers. Reactive power is provided by generators, synchronous condensers, or electrostatic equipment such as capacitors and directly influences electric system voltage. It is a derived value equal to the vector difference between the apparent power and the real power. It is usually expressed as kilovolt-amperes reactive (kVAR) or megavolt-ampere reactive (MVAR)
Reactive suspension
Reactivity Adjustment Factor
(RAF) An NMOG adjustment used in the certification of vehicles to the California emission standards to reflect reduced ozone forming potential of a fuel, especially alternative fuels.
Reactor one-way clutch
Trucker slang for hear as in ‘Can you read me there Baylor.’
Readily accessible
Having direct access without the need of moving or removing any panel, door or similar covering of the item described. Compare Reasonably accessible
Read only memory
(ROM) A non-volatile memory that stores information permanently. Information is placed into the memory at the time of manufacture and cannot be altered after the manufacturing process.

A pure chemical substance that is used to make new products or is used in chemical tests to measure, detect, or examine other substances.

Real power
  1. For sinusoidal quantities in a two-wire circuit; the product of the voltage, the current, and the cosine of the phase angle between them. In a polyphase circuit; the sum of the active powers of the individual phases.
  2. The component of electric power that performs work, typically measured in kilowatts (kW) or megawatts (MW)–sometimes referred to as Active Power. The terms real or active are often used to modify the base term power to differentiate it from Reactive Power and Apparent Power
Real-time four-wheel drive
An automatic four-wheel drive engagement by means of an electro-hydraulic clutch or a viscous coupling incorporated in the drivetrain.
  1. To enlarge (e.g., worn valve guides) with a Reamer.
  2. To finish a hole accurately with a rotating fluted tool.
  3. To finish a drilled or punched hole very accurately with a rotating fluted tool of the required diameter.
  1. A conically or cylindrically shaped tool with longitudinally cut teeth for manual or machine operation, used for precision finishing of bores.
  2. Tool used for enlarging holes previously formed by drilling or boring.
The back of a vehicle or component.

Rear apron
The shaft on which the back wheels revolve.

Rear axle crossmember
A tubular frame member at the rear of the body shell that incorporates the mounting points for the rear axle, e.g., on the VW Beetle and the Porsche 911.
Rear axle differential
A differential situated in the final drive of the transmission assembly in a conventional rear-wheel drive vehicle.
Rear axle housing
Rear axle housingRear axle housing

The component which connects the drive shaft to the axle shafts.

Rear axle ratio
The number of times the rear wheels turn compared to a particular transmission speed. The higher the rear axle ratio, the slower the engine can run and still allow the vehicle to achieve a given speed. Also called Final axle ratio.
Rear-axle split
Rear bulkhead
The vertical panel across the width of the car that extends behind the rear seat backrest and separates the interior from the trunk.
Rear bumper
A protective bar which extends laterally across the back of a vehicle.
Rear bumper skirt
A rear bumper with integral skirt; a large plastic molding.
Rear cabin pillar

Rear corner panel
The bottom corner of the rear fenders. For manufacturing reasons, often a separate panel.
Rear corner valance
The bottom corner of the rear fenders. For manufacturing reasons, often a separate panel.
Rear deck
The surface of the rear of a sedan which includes the lid of the trunk.
Rear deck panel
The sheet metal panel extending from the bottom of the rear window to the rear panel and enclosing the cutout for the trunk lid, extending sideways to the top of both rear fenders. In some cases, this panel covers only the area between the bottom of the rear window and the front edge of the trunk lid.
Rear derailleur
Rear derailleurRear derailleur

A bicycle component that moves the chain across the rear cogs thus changing the gear ratio and achieving what is referred to as a gear shift.

Rear differential
A differential situated in the final drive of the transmission assembly in a conventional rear-wheel drive vehicle.
Rear end
The back part of the body shell, extending approximately from the rear seat pan to the rear apron of the car, incorporating the trunk floor.
Rear end lift
The tendency of the back of a speeding vehicle to rise, reducing traction. It can be counteracted by a spoiler.
Rear engine
An engine located at the rear of a vehicle but outside the wheelbase (i.e., behind the rear wheels). Compare Front engine and mid-engine car.
Rear fender
The body panel which partially encloses a rear wheel.
Rear fog lamp
A red light with the same intensity as a brake light.
Rear fog light
A red light with the same intensity as a brake light.
Rear head restraints
(rhr) head rests located on the back passenger seats.
Rear-hinged door
A older type of door construction that had the hinges at the rear of the door so that the opening was toward the front (i.e., opposite to modern car doors).
Rear lamp cluster
A group of lights at the rear corners of a vehicle, commonly comprising tail lamp, brake lamp, back-up lamp, rear fog lamp, reflector, and signal light.
Rear light surround
A separate panel spot-welded at the juncture between the trailing edge of the rear fender and the rear valance to provide a mounting base for the rear lights.
Rear license plate lamp
A white light illuminating the rear license plate.
Rear license plate light
A white light illuminating the rear license plate.
Rear Loader
A refuse truck that is loaded at the rear usually with some kind of compacting mechanism.
Rear Main Seal Bearing
Rear panel
A British term for Back panel.
Rear quarter panel
Often integral with the rear fender on newer cars, but a separate panel above the rear fender. There may be both an inner and outer panel which makes up the construction.
Rear quarter valance
Rear seat belt
An inertia reel belt attached at each end of the rear seats; a passenger riding in the middle of the rear seats must be satisfied with just a lap belt, which many safety experts regard as inadequate. Some manufacturers (notably those from Scandinavia) are tackling the somewhat costly problem and providing secure lap and shoulder belts for all passengers riding in the rear seats.
Rear seats
Rear sets
Racing-style footrests mounted toward the rear of the machine to allow the rider to adopt a racing crouch.
Rear shelf
The interior shelf extending over the trunk at the level of the top of the rear seats.
Rear side window
One of several types of side body glass the side window between theB-posts and C-posts of two-door sedans and coupes, the rearmost side window of station wagons between the C-post and D-post, i.e., behind the rear seat backrest, and the third side window found on some four-door sedans behind the rear side doors.
Rear spoiler
Rear spoilerRear spoiler

An aerofoil mounted on the rear deck or trunk, typically made of shock-resistant polyurethane with paintable matt black finish. It is effective only at high speeds, but frequently used for the sake of appearance. Most sports cars are equipped with front and rear spoilers (air dams and rear spoilers) to improve the aerodynamic performance by reduced lifting force.

Rear suspension
The axles, springs, and linkages which control the movement of the rear wheels.

Rear tack strip
A fixed or hinged bar on a convertible top which holds the rear end of the hood against the rear deck.
Rear track
The distance between the center of the left rear wheel and the center of the right rear wheel when the vehicle is set to its normal ride height and wheel alignment specifications. It is not necessarily the same as the front track
Rear triangle
A Bicycle frame triangle formed by the Chainstays, Seatstays, and the Seat tube.
Rear valance
A separate panel set below the rear panel which extends approximately from behind the rear bumper downward to protect the rear end from splashes of mud. In designs with a single-piece rear panel that incorporates the rear valance, the whole area is sometimes referred to as the rear valance or rear panel.
Rearview mirror
An interior mirror which allows the driver to see behind him.
Rear wash/wipe system
An electrical system for cleaning the rear window, comprising a water pump, reservoir, and wiper.
Rear-wheel drive

  1. A configuration in which the rear wheels of the vehicle are driven.
  2. A vehicle that is pushed by its rear wheels, rather than pulled by its front wheels, has rear-wheel drive. In most configurations, the engine and transmission (usually located at the front of the vehicle) are linked to the differential by a long driveshaft. However some rear-wheel drive vehicles (like the older VW and Porsche) have the engine at the back of the vehicle where the engine is combined with the transaxle.
Rear-wheel drive transaxle
A rear-wheel drive construction incorporating a transmission-differential unit placed between the rear wheels of a front-engined car. The engine may be a front engine (as in most cars and all trucks), a mid-engine (as in some sports and racing cars), or a rear engine (as in some city cars, VW Beetle, the Porsche 911 series, and most buses); RWD ensures good acceleration without wheelspin even on cars with powerful engines; on most small cars,RWD has been superseded by front-wheel drive.
Rear wheel skirt
Rear wheel spat
British term for Fender skirt.
Rear window
The central window at the rear of a vehicle. Although the American term is backlight, most Americans still call it the rear window or back window.

Rear window heater system
A heating element that removes the fog, mist, or even ice from the inside and outside of the backlight (i.e, rear window).
Rear window heating
Rear window louvers
A plastic molding attached to the rear window which deflects sun rays to keep the interior cool; usually hinged to lift up for easy window cleaning. Also spelled louvre
Rear wiper
A window wiper that cleans the rear window.
Reasonably accessible
Having access to, but which first may require the removal of a panel, door or similar covering of the item described. Compare Readily accessible
A model of automobile manufactured by Buick Division of General Motors from 1988-91
Réaumur scale
A temperature scale where the freezing point of water at 1 atmosphere is 0° and its boiling point is 80° at the same pressure. Thus 1°C = 0.8°R. The scale was named after the French physicist, René Antoine Ferchault de Réaumur (1683-1757)
Metal rod reinforcement for concrete roadway and structures to provide support
RebelClick image for books on

An automobile manufactured by AMC

Reboard system
A child restraint system typically installed backwards on the front passenger seat and having the benefit that the child’s relatively heavy head is pressed into the back of the child seat instead of being displaced forward in a frontal crash. A system initially available only for babies, but originating from Sweden, they are increasingly offered for children up to six years old; some reboards cannot be used in conjunction with a passenger-side air bag system.
To grind out a worn or damaged cylinder usually .25 mm or (.01′) at a time to fit an oversize piston.
The action of a shock absorber to spring back to its fully extended state. The opposite of rebound is Jounce.

Rebound clip
Rebound clipRebound clip

A metal clip that holds the leaves of a multi-leaf spring together to keep them from separating sideways.

Rebound damping
While compression damping controls the movement as the shock compresses as it hits a bump, rebound damping controls the movement as the shock extends back to its relaxed position.
Rebound stroke
The downstroke of a piston in a damper or shock absorber. Compare compression stroke.
To disassemble a particular device, clean it thoroughly, replace worn parts, and reassemble it. Also called overhauling or recondition. Engines, clutches, carburetors, and brakes are sometimes rebuilt as part of the maintenance or restoration of older vehicles. You can rebuild a part yourself with a kit containing instructions and part replacements, or you can buy a rebuilt part and turn in your old part for a core charge.
Rebuilt engine
An engine reassembled using either new parts or reconditioned components.
An advanced co-firing technique using natural gas to reduce pollution from electric power plants.
Abbreviation for Calibration Adjustment
The release of heat as an object cools
  1. Adding a top strip of synthetic or reclaimed rubber to buffed and roughened surface of a worn tire.
  2. The top strip itself

The action of bringing a product back to its full or original level. Recharging a battery brings the voltage back to its recommended level. Recharging the air conditioner means filling the system with refrigerant.
  1. (e.g., of radio remote control system) device that receives incoming electrical or radio signals. The opposite is Transmitter.
  2. A steel tubing and channel structure that accepts the ball-mount platform of a removable trailer coupler.
Storage tank and filter for liquid refrigerant and containing a drying agent to remove moisture from circulating refrigerant. Also called Receiver-drier.
  1. A device on the high side of an air-conditioning system, somewhere between the condenser and the expansion valve, which stores excess refrigerant and removes moisture from the refrigerant; consists of a tank, a filter, a drying agent, a pick-up tube, and, on some units, a sight glass. Also called Receiver-dehydrator
  2. A container for storing liquid refrigerant and a desiccant. Used in Chrysler Corporation and some import vehicles Compare Accumulator-drier.
Receiver extension
Used with Receiver Hitch Racks when the rack need to clear obstacles on the back of the vehicle (such as a spare tire rack).
Receiver heating element
Electrical resistance mounted in or around liquid receiver. It is used to maintain head pressures when ambient temperature is low.
Receiver Service Valve
Receiver unit
Recessed Head
A screw head, having specially formed indentations or recesses centered on the head, into which a suitably formed driver fits.
Recessed spark position
A position where the spark gap is actually in the shell of the spark plug. It is used for racing and special engines.
Rechargeable battery
Back and forth motion in a straight line.
Reciprocating action
A back-and-forth or up-and-down movement such as the action of the pistons.
Reciprocating compressor
  1. A positive displacement compressor with pistons that move back and forth in cylinders; rarely used for supercharging, more frequently used for air conditioning
  2. Compressor which uses a piston and cylinder mechanism to provide pumping action.
Reciprocating engine
An engine with a piston that moves to and fro, coming to a standstill at each reversal.
Reciprocating pump
Reciprocating single piston pump
A pump having a single reciprocating (moving up and down or back and forth) piston.
A back-and-forth or up-and-down movement such as the action of the pistons.
Recirculated air
Air removed from a space and intended for reuse as supply air.
Recirculating ball
Recirculating ball and nut steering
Recirculating-ball-and-nut steering
A very popular type of Steering gear. It uses a series of Ball bearings that feed through and around and back through the grooves in the Worm gear and nut on the Steering shaft. The turning forces are transmitted through these Ball bearing to a sector gear on the pitman-arm shaft. When the steering wheel is turned, the worm gear on the end of the steering shaft rotates and the movement of the recirculating balls causes the ball nut to move up and down along the worm. Movement of the ball nut is carried by teeth to the sector gear which in turn moves with the ball nut to rotate the pitman-arm shaft and activate the Steering linkage. The balls recirculate from one end of the ball nut to the other through a pair of ball return guides. This system is also called ball-and-nut steering or worm-and-recirculating-ball steering.
Recirculating ball gearbox
Recirculating Ball gearboxRecirculating Ball gearbox

A special version of the worm-and-nut steering in which ball bearings circulate between the nut and worm to reduce friction. Turning the steering wheel rotates the worm gear, which causes the ball nut rack to move up or down. Teeth on the outer edge of the ball nut rack mesh with the sector gear so that as the rack moves, it swivels the sector gear and Pitman arm. The ball bearings in the grooves reduce friction.

Recirculating ball steering
A special version of the worm-and-nut steering in which ball bearings circulate between the nut and worm to reduce friction. Turning the steering wheel rotates the worm gear, which causes the ball nut rack to move up or down. Teeth on the outer edge of the ball nut rack mesh with the sector gear so that as the rack moves, it swivels the sector gear and Pitman arm. The ball bearings in the grooves reduce friction.
Recirculating ball worm and nut
Recirculation system
Recirculation Valve
Reclaimed rubber
Reprocessed rubber (tires, inner tubes, rubber novelties), either synthetic or natural, used as an adhesive base. Because of characteristic advantages of low cost, good physical properties, wide tack range, tolerance of surface preparation, and high wet strength, these are the most widely used of the rubber based adhesives
A colloquial term for Reconditioned engine.
Reconditioned engine
A worn engine that has been given a new lease of life by reboring the cylinders, regrinding the crankshaft journals and generally replacing any worn or damaged parts.
Road work which includes improving drainage features, rebuilding the road base, placing a new pavement, and shoulder work. Prior to reworking the roadbed, old culverts may be replaced, 4′ plastic drain tile may be installed along the edge of pavement, and ditches may be cleaned or even relocated. The base work could be full-depth reclamation, or it could be placement of a new gravel base. The pavement will then be one or more layers of asphalt concrete. The finished driving surface could be an asphalt concrete ‘top mix,’ or a surface treatment. Finally, the shoulders will usually have to be reconstructed to match the elevation of the new road surface. County residents can expect to see days and weeks of activity with many varied pieces of equipment and trucks, interspersed with weeks of little to no activity while a previously completed treatment cures, and scheduling allows for the next stage.
Recording ammeter
Electrical instrument which uses a pen to record amount of current flow on a moving paper chart.
Recording thermometer
Temperature measuring instrument’ which has a pen marking a moving chart.
Recovery Act
Recovery/recycling equipment
Equipment that must now be used when servicing air conditioner systems. This equipment captures refrigerant removed from an air conditioning system and stores or recycles it.
Recovery system
Recreational vehicle

  1. Any vehicle (motorized or trailered) in which temporary camping is done. They are divided into seven categories


  2. A British term for any vehicle used for pleasure rather than business or transport (e.g., dune buggy, quad) (i.e., an ATV).
Rectangular headlight
A modern shape of headlight as opposed to the traditional circular headlight.
Rectangular-section ring
A compression ring with a rectangular cross-section.
The process of changing AC to DC.

A device used to change AC into DC. Some small motorcycles use a single Diode (half-wave rectifiers) for this purpose, the overwhelming majority use four diodes connected in a bridge which yields full-wave rectification.

Rectifier diode
A semiconductor diode in an alternator that converts alternating current to direct current.
Rectifier, electric
Electrical device for converting ac to DC.
Rectifier pack
A diode heat sink with diodes in an alternator.
RecumbentActionBent Recumbent

A bicycle in which the rider sits low between the two wheels. The seat is L-shaped. The rider’s back is against the upright portion of the seat. His feet are almost straight forward. The pedals are ahead of the front wheel. The handlebar is often located below the rider.

Recuperative coil
Secondary coil in glycol water forced-air furnace which extracts latent heat from combustion gases.
The process of recovering and reusing materials.

  1. Passing of flue gases from combustion in a furnace to a secondary heat exchanger to remove latent heat.
  2. The process of converting materials that are no longer useful as designed or intended into a new product.
Recycling car
A car built with recycled materials and designed so as to facilitate recycling.
Recycling Equipment
Red Book
A listing of current vehicle prices, based on age, condition, and optional equipment; published by National Market Reports.
Red flag
A solid red flag is used to stop the race immediately. Generally races are stopped for bad accidents or weather. Occasionally, a multiple car pileup will halt a race. Wreckers and fire marshals clear the track of cars, debris and fluids. Alternatively, rain makes the surface of the race track dangerous. Once NASCAR officials authorize the race to start again, a green flag resumes the race.
Red Heat
Red lead
(pronounced LED) A poisonous, bright-red powder, soluble in excess glacial acetic acid and dilute hydrochloric acid; used for corrosion protection.
Red line
  1. Top recommended engine rpm. If a Tachometer is used, it will have a mark (red line) indicating maximum rpm. Some tachometers mark the red line with a colored sector. Others have two lines the lower one marking the maximum allowable sustained engine rpm, the higher line indicating the absolute maximum rpm.
  2. (RL) Tires with a red Concentric line which were marketed in the late ’60s and early ’70s.
Abbreviation for Reduction Oxidation Converter
REDOX potential
A measurement of the state of oxidation of a system.
Reduced body diameter
Where the shoulder of a fastener equals the pitch diameter or less, which means the shoulder is smaller than the outside diameter of the threads. It would indicate that a fastener was not extruded during its manufacture. Also called Undersize body
Reduced Crude Oil
Crude oil that has undergone at least one distillation process to separate some of the lighter hydrocarbons. Reducing crude lowers its API gravity, but increases the handling safety by raising the flash point.
Reduced inflation
Lowering tire pressures to increase flotation in soft ground conditions such as mud or soft sand.
Reduced shank
A shank whose diameter approximately equals the effective pitch diameter.
The Solvent that is used to thin Enamel.

Reducer valve
Reducing adapter
An adapter whose male end for the socket is smaller than the female end for the drive handle. Opposite to Increasing adapter.
Reducing agent
  1. Any substance, such as the base metal (iron) or the sulfide ion that will readily donate (give up) electrons. The opposite of an oxidizing agent.
  2. A material which adds electrons to an element or compound in chemical reactions, i.e., which increases the positiveness of its valence.
Reducing catalyst
A catalyst such as rhodium which converts nitrogen oxides into harmless nitrogen and oxygen in a reducing catalytic converter. Compare oxidizing catalyst.
Reducing flame
An oxygen-fuel gas flame with a slight excess of fuel gas.
Reducing furnace
A section in continuous galvanizing lines in which the oxygen content of steel surfaces is reduced at 900-980°C by means of hydrogen.
A chemical reaction in which an element gains electrons, i.e., has an increase in positive valence. Compare Oxidation.

Reduction Axle
Reduction effort
Reduction gearbox
A gearbox located at the wheels, which reduces the drive speed and may also increase ground clearance; often found on 4WD off-road vehicles.
Reduction gearing
Reduction of area
  1. Difference in cross sectional area of a specimen after fracture, as compared to original cross sectional area.
  2. A measurement like elongation which is related to the tensile strength of a fastener. While elongation measures the length of a fastener stretched to its breaking point compared to its original length, reduction of area measures the diameter of a fastener just before breaking compared to its original diameter.
Redwood viscosity
The number of seconds required for 50 ml. of an oil to flow out of a standard Redwood viscosimeter at a definite temperature; British viscosity standard.
A part of a reed valve made of flexible steel, or of glass fiber reinforced resin, attached to the valve case and normally closed. The reeds are designed to open readily under pressure from the incoming mixture, but will close rapidly once the pressure inside the crankcase reaches that of the surrounding atmosphere; in this way, the maximum amount of mixture is admitted and any back-leakage is prevented.
Reed and Prince
Phillips ScrewdriverReed and Prince Screwdriver Tip

A screwdriver with a sharp pointed tip that is shaped to fit the crossed slots in the heads of Phillips screws. It is distinguished from a Phillips screwdriver which has a blunted tip.

Reed stop
A component of a Reed valve used to limit upward travel of the reed.
Reed valve
  1. A one-way valve used in a Two-cycle engine. It is made of a flat strip of metal that lies on the floor of the crankcase over a hole connected to the carburetor. As the piston moves up, the vacuum developed in the crankcase lifts the reed valve off the hole. The vacuum causes the fuel-air mixture to flow from the carburetor into the crankcase. Then, as the piston starts to move down, pressure increases in the crankcase pushing the reed valve down, closing the hole and sealing the crankcase.
  2. Wafer-thin metal plate located in the valve plate of an automotive compressor which act as suction and discharge valves. The suction valve is located on the underside of the valve plate; the discharge valve is situated on the top.
Reed valve induction timing
Using a Reed valve located in the intake system to control induction timing.
  1. A refrigeration unit which is mounted on a large truck to cool the contents in the trailer.
  2. A refrigerated trailer with insulated walls and a self-powered refrigeration unit. Most commonly used for transporting food.
  3. A ship designed for carrying goods requiring refrigeration.
Reefer container
An insulated container fitted with a refrigeration unit for carrying cargo requiring temperature control.
A revolving, often cylindrical device for winding up or letting out cord, wire, or strap.

Reel Change
Reel seat belt
Abbreviation for Reference

A general term for reconditioning of the interface between valves and their seats in the cylinder head; depending on valve seat condition, refacing may involve lapping, grinding, or cutting.
Reference ignition pattern
An oscilloscope pattern of an intact ignition system for comparison purposes.
Reference input
In a closed-loop control, the reference input is fed to a controller that changes a controlled variable in a controlled system to achieve a certain output condition or actual value.
Reference mark sensor
A magnetic pick-up attached to the flywheel for sensing the crankshaft position and transferring the signal to the electronic control unit, which calculates the ignition point; the reference mark sensor scans a pin or a hole in the flywheel and produces one output signal per crankshaft revolution.
Reference pressure
The fuel bowl is vented to the outside air to maintain a constant (atmospheric) pressure on the fuel, thus maintaining a constant fuel level as a point of reference for the other system in the carburetor.
Reference signal
A signal sent to the ECU, generally by the vehicle’s fastest-moving wheel, which the ECU uses for comparison with the signals from decelerating wheels
Reference temperature
The temperature at which measuring tools and pieces being worked on must have the specified measurements; the reference temperature 20°C applies to all statements of technical measurements unless the contrary is expressly stated.
Reference voltage
A voltage provided by a voltage regulator to operate potentiometers and other sensors at a constant level.
Refined petroleum products
Refined petroleum products include but are not limited to gasolines, Kerosene, distillates (including No. 2 fuel oil), liquefied petroleum gas, asphalt, lubricating oils, diesel fuels, and residual fuels.
A plant used to separate the various components present in crude oil and convert them into usable products or feedstock for other processes.

Refinery fuel
Crude oil and petroleum products consumed at the refinery for all purposes.
Refinery gas
Noncondensate gas collected in petroleum refineries.
Refinery Gases
Refinery MTBE Plants
Refinery Oxygenate Plants
Refinishing paint
A paint sold specifically for resprays; many paint formulas used in the factory are not suited for respray equipment, so special paints for the repair trade are required.
Refinish system
The complete product lines and product support offered by many paint manufacturers for respray operations in body shops; these include all materials from primers and thinners to the topcoat plus additional respray products; all products are matched for optimum results.
Closure of a plant for the purpose of plant conversion or retooling.
The ratio of reflected luminous flux to that reflected from an ideal, perfectly reflecting surface when similarly illuminated.
Reflective film
Transparent covering for glass that helps keep out heat from the sun.
The ratio of the energy carried by a wave after reflection from a surface to its energy before reflection.
  1. A part of a headlight which receives light from the bulb and reflects it back through the lens.
  2. A part of a rear lamp cluster which reflects the light from headlights behind.
Reflux Boiling Point
Reformate gas
The fluid which exits the fuel reformer and acts as feed to the fuel cell stack.
A vessel within which fuel and other gaseous recycle stream(s) (if present) are reacted with water vapor and heat, usually in the presence of a catalyst, to produce hydrogen rich gas for use within the fuel cell power plant.
The thermal or catalytic conversion of a hydrocarbon fuel into more volatile products with higher BTU ratings.

Reformulated Gasoline

  1. Gasoline that has had its composition and/or characteristics altered to reduce vehicular emissions of pollutants, particularly pursuant to EPA regulations under the CAA.
  2. Gasoline different from that of gasolines sold in 1990, to
    • include oxygenates
    • reduce the content of Olefins, aromatics and volatile components, and
    • reduce the content of heavy hydrocarbons to meet performance specifications for ozone-forming tendency and for release of toxic substances (Benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and polycyclic aromatic hydrocarbons) into the air from both evaporation and tailpipe emissions.
  3. Finished gasoline formulated for use in motor vehicles, the composition and properties of which meet the requirements of the reformulated gasoline regulations promulgated by the U.S. Environmental Protection Agency under Section 211(k) of the Clean Air Act. It includes gasoline produced to meet or exceed emissions performance and Benzene content standards of federal-program reformulated gasoline even though the gasoline may not meet all of the composition requirements (e.g., oxygen content) of federal-program reformulated gasoline. Note: This category includes Oxygenated Fuels Program Reformulated Gasoline (OPRG). Reformulated gasoline excludes Reformulated Blendstock for Oxygenate Blending (RBOB) and Gasoline Treated as Blendstock (GTAB).
  4. Fuel with less Volatility and reduced levels of toxic Hydrocarbons.
Reformulated gasolines

  1. Fuels with less Volatility and reduced levels of toxic Hydrocarbons.
  2. Gasoline blended with pollution reducing additives
The liquid used in refrigeration systems to remove heat from the evaporator coils and carry it to the condenser. It absorbs and gives up heat as it changes from a liquid to a gas to a liquid. Freon-12 was a common automotive refrigerant, but it has been replaced by C134A.

The name applied to refrigerant generally used in automotive air conditioning systems and refrigerators. Also called Freon-12.
Refrigerant charge
Quantity of refrigerant in a system.
Refrigerant control
  1. Device which meters flow of refrigerant between two areas of a refrigerating system. It also maintains pressure difference between high-pressure and low-pressure side of the mechanical refrigerating system while unit is running.
  2. Device used to regulate flow of liquid refrigerant into evaporator. Can be a capillary tube, expansion valves, or high-side and low-side float valves.
Refrigerant cylinder
Cylinder in which refrigerant is stored and dispensed. Color code painted on cylinder indicates kind of refrigerant.

Refrigerant Drum
Refrigerant dye
Coloring agent that can be added to refrigerant to help locate leaks in a system.
Refrigerant System
Refrigerated Foods cargo
Truck content carried in refrigerated cargo bodies. Ice is included in this category. Refrigerated foods must be both refrigerated and food for human consumption.
Refrigerated truck
A commercial vehicle (usually a Straight truck) or a Reefer trailer equipped to maintain below-ambient temperatures.
Refrigerated Van
A cargo body style typified by a totally enclosed box with a refrigeration unit.
Refrigerating System
Refrigeration cycle
The complete circulation of refrigerant through an air conditioning system as it changes temperature and pressure, i.e., changes its state from vapor to liquid, then back to vapor. Air-conditioning refrigerant in vapor form is pressurized in the compressor, air-cooled in the condenser, and becomes a liquid which passes through the receiver-drier into the expansion valve where it expands into low-pressure liquid. It then flows through the evaporator where it expands again and starts to boil, absorbing heat from the core and cooling the air going into the passenger compartment. The compressor draws off the low-pressure vaporized refrigerant and recycles it.

Refrigeration oil
A highly refined lubricating oil which is free of contaminants such as sulfur, moisture, and tar.
Refrigeration unit
A device that lowers the temperature through a mechanical process. In a typical refrigeration unit, electricity powers a motor that runs a pump to compress the refrigerant to maintain proper pressure. (A refrigerant is a substance that changes between liquid and gaseous states under desirable temperature and pressure conditions.) Heat from the compressed liquid is removed and discharged from the unit and the refrigerant then evaporates when pressure is reduced. The refrigerant picks up heat as it evaporates and it returns to the compressor to repeat the cycle. A few refrigeration units use gas (either natural gas or LPG) in an absorption process that does not use a compressor. The gas is burned to heat a chemical solution in which the refrigerant has been absorbed. Heating drives off the refrigerant which is later condensed. The condensed refrigerant evaporates by a release of pressure, and it picks up heat as it evaporates. The evaporated refrigerant is then absorbed back into the chemical solution, the heat is removed from the solution and discharged as waste heat, and the process repeats itself. By definition, refrigerators, freezers, and air-conditioning equipment all contain refrigeration units.

Refueling Emissions
VOC vapors that escape from the vehicle fuel tank during refueling. Storage II pump controls and onboard refueling vapor recovery systems (ORVR) are intended to control these emissions.
Refueling Vapor Recovery
Refundable deposit
This is a refundable deposit required at lease inception. In some cases it may be used to satisfy the final monthly payment. It is sometime called a security deposit.
Refuse-derived fuel
(RDF) A fuel produced by shredding municipal solid waste (MSW). Noncombustible materials such as glass and metals are generally removed prior to making RDF. The residual material is sold as-is or compressed into pellets, bricks, or logs. RDF processing facilities are typically located near a source of MSW, while the RDF combustion facility can be located elsewhere.
Refuse truck
A cargo body style truck often with a hydraulic packing mechanisms or hydraulic arms for lifting dumpsters. Included are roll-offs, vehicles used for transporting refuse containers. Roll-off refuse trucks have rails or a flat bed and a hoist for loading and unloading the refuse container. Also called garbage truck.
Refuse Body
A cargo body designed for loading and hauling rubbish.
Buick RegalClick image for books on
Buick Regal

A model of automobile manufactured by the Buick division of General Motors from 1988-2004

Regenerative braking
A system in which an electric motor can be switched to a generator mode when braking, so that the kinetic energy involved may be stored in the battery.
  1. To align with. The two-stroke piston is provided with cut-outs that line up with the intake ports as the piston moves up and down in the bore, i.e., they register with the ports. The fresh charge can thus enter the crankcase.
  2. Combination grille and damper assembly covering an air opening or the end of an air duct.
Registered keeper
A British term for a person who keeps the car, i.e., who is registered and pays tax and insurance for the car, but is not necessarily the owner or the driver.
Registered owner
The person who owns the car, i.e., the car is registered in his name and he pays the license, tax, and insurance for the car.
Registered tons
  1. Motor vehicle ownership that is filed with the province/state.
  2. The act of entering the details of a new vehicle in a supervised record.
Registration document
Papers giving details of a vehicle, including its manufacturer, date of registration, engine and chassis numbers, and owner’s name.

Registration number
A unique sequence of letters and numbers assigned to a vehicle when it is registered, usually indicating the year and place of registration, displayed on the vehicle license plate.
Registration plate
  1. To smooth and polish again (e.g., valve seats).
  2. A resin batch material produced by regrinding thermoplastic scrap and waste; such recycled material can be used to produce plastic parts which are not critical in terms of engineering properties or color, such as wheel arch liners or battery cases. The opposite is Virgin resin.
Regrooveable tire
The act of cutting new tread grooves into the crown of the tire after the original tread is worn down. A practice which is legally forbidden in many places.
Regular Cab
Regular CabRegular Cab

A pickup with two doors (one on each side of the vehicle) and a bed at the back.

Regular gasoline
  1. Gasoline which has the normal amount of octane and is less than premium or high-test gasoline.
  2. Gasoline having an antiknock index, i.e., octane rating, greater than or equal to 85 and less than 88.
Regular grade gasoline
A grade of unleaded gasoline with a lower octane rating (approximately 82) than other grades. Octane boosters are added to gasoline to control engine pre-ignition or knocking by slowing combustion rates.
Regular threading
A common name for right-hand thread
Regulated proportioning valve
Regulating Switch
Regulating system
Regulating valve
Regulation Capacity
Regulation traction control system
  1. The device found in the panel of a vehicle door which lifts and lowers the window. It may be operated manually or electrically.
  2. Any device which controls fluid (gas or liquid) flow, pressure, temperature, voltage, etc.
Regulator Evaporator
Regulator valve
Regulator Valve Three And Four-port
Regulator Valve Two-port
Reheating coils
A part of some air-conditioning systems. Electric coils in air ducts used primarily to raise the temperature of circulated air after it was over-cooled to remove moisture. Some buildings have reheating coils as their sole heating source.
Reid Vapor Pressure

  1. An indirect measure of the rate at which petroleum liquids evaporate. It is the absolute vapor pressure of a crude oil, or of single or mixed liquid petroleum products, as measured by the Reid Method.
  2. A standard measurement of a liquid’s vapor pressure in psi at 38°C. It is an indication of the propensity of the liquid to evaporate.
  3. Normally measured in psi, RVP is a measure of the front end volatility of gasoline. This is important for getting a carburetor car started in cold weather. Summer RVP = 7 psi, and winter RVP = 13.5 psi.
To increase the strength of plastics by filling them with whiskers of glass, metal, fibers, etc.

Reinforced concrete
A strongly compressed concrete with steel or iron bars, rods, or mesh
Reinforced filler paste
Reinforced plastic
Reinforced reaction injection molding

  1. A reaction injection molding of reinforced plastics.
  2. The term also refers to the material produced by this technique.
Any material, usually rubber and fabric, vulcanized to the tire to return strength to the cord body upon an injury.

Reinforcement of weld
Excess metal on the face of a weld.
Relative atomic mass
(ram) Mass of atoms of an element formerly in atomic weight units but now more correctly given on the unified scale where 1 u is 1.660 x 10-27kg, where u is the atomic mass unit. For natural elements with more than one isotope, it is the average for the mixture of isotopes.
Relative density
The ratio of the mass of a given volume of a substance to the mass of an equal volume of water at a temperature of 4°C. The older term was Specific gravity
Relative humidity (RH)
  1. A dimensionless ratio of the actual vapor pressure of the air to the saturation vapor pressure
  2. Ratio of (difference between) amount of water vapor present in air to greatest amount possible at same temperature.
  1. An electro-magnetically operated switch used to make and break the flow of current in a circuit. As low amperage current is passed through one circuit of the relay, it switches and permits a greater current through another line. For example, when installing Auxiliary lights with a heavy draw, the stock light switch may not be able to take the current. Thus a relay is installed so that when the light switch is turned on, low current is sent to the relay. The relay closes the circuit of heavy wiring directly from the battery to the lights. Also called Cutout and Circuit breaker.
  2. An automatic device which controls the setting of a valve, switch, etc. by means of an electric motor, solenoid, or pneumatic mechanism.
  3. An electromagnetic switch using a small amount of current in one circuit to control a second circuit using a greater current flow.
  4. A common practice in the less-than-truckload industry, in which one driver takes a truck for 8 to 10 hours, then turns the truck over to another driver, pony express style. Also called relay driving
  5. An electrical switch that transmits impulses from one component to another
Relay driving
A common practice in the less-than-truckload industry, in which one driver takes a truck for 8 to 10 hours, then turns the truck over to another driver, pony express style.
Relay emergency valve
A relay valve which also provides for automatic application of the trailer brakes in case of a breakaway or loss of pressure in the trailer supply (emergency) line.
Relay lever

Relay rod
An intermediate rod between the pitman arm and idler arm.
Relay valve
Release agent
A substance to prevent a molding, i.e., a GRP part, from sticking to the mold and to facilitate its removal from the mold; as opposed to release wax, this is marketed only in liquid form.
Release bearing
Release button
A button at the end of the park brake lever which, when depressed, allows the pawl to be released from the ratchet.
Release finger
Release fork
Release Hitch Pin
Release lever
Release skewer
Release tool
Release wax
Releasing fluid
Penetrating oil for loosening seized parts.
The quality of an item to perform a required function under stated conditions for a stated period of time.

  1. Amount one surface is set below or above another surface.
  2. The amount one plane surface of a piece is set below or above another plane, usually for clearance or for economy in machining.
Relief passage

Relief valve
  1. A safety valve designed to forestall the development of a dangerous condition by relieving either pressure, temperature, or vacuum in a fluid based system.
  2. A valve in the air pump of an air injection system which dumps part of the air at high pump speeds to prevent pump damage. It may be combined with the air gulp valve.
  3. Safety device on a sealed system. It opens to release fluids before dangerous pressure is reached.
To remove, by grinding, the small lip of metal between the valve seat area and the cylinder and removing any other metal considered necessary to improve the flow of fuel mixture into the cylinders. Porting is generally done at the same time.

Relieved shank
Removal of some metal from around racing engine valves and between cylinder and valves to facilitate flow of gases.

To replace the brake shoes in drum brakes.
  1. A force working against the passage of magnetic lines of force (flux) through a magnetic substance.
  2. The characteristic of a magnetic material which resists the flow of magnetic lines of force through it
Reluctance Sensor
A ferrous metal piece attached to the distributor shaft. Made up of teeth of which the number are the same as the number of engine cylinders. As the reluctor teeth pass through the pick-up magnetic field, an alternating current is generated in the pick-up coil. Also called an Armature

The process of taking a used part and returning it to Original equipment (OE) Specifications through disassembly and cleaning of the core, testing, and remachining or replacement of worn components.
Re-metalling the bearings
A bearing repair method used on pre-war engines with poured bearings instead of Babbitt metal inserts. The Babbitt metal is poured into the bearing surfaces and is then scraped until a correct bearing surface is established.

Remote bulb
A sensing device connected to the expansion valve by a capillary tube. The bulb senses the temperature of the evaporator outlet pipe and controls the expansion valve accordingly.
Remote choke
Vacuum diaphragm is mounted on the carburetor, but the bimetal spring is mounted either on a pad on the intake manifold or in a heat well in the exhaust man. Choke lever is operated by a mechanical linkage rod from the bimetal spring. Also called Divorced choke.
Remote control
  1. The control of something from a distance.
  2. The device used for this.
Remote controller
Energy control device capable of controlling multiple devices. It can be located away from the devices it is controlling.
Remote-control locking
A central locking device operated by a remote control from outside the car.
Remote keyless entry
A system where the door locks can be opened or locked by a small hand-held switching device located several metres/feet away. Some also contain a panic button that causes the lights to flash and the horn to honk if an intruder is seen near the vehicle. Most remote keyless entry devices turn on the vehicle’s interior lights while unlocking the driver’s door.
Remote mirror
An outside mirror that is adjusted by a toggle device inside the passenger compartment. Older styles relied on a cable that transferred physical movement from the toggle to the mirror. On newer vehicles, the mirror is controlled by electrical controls.
Remote power element control
Device with sensing element located apart from operating mechanism it controls.
Remote starter switch
A special automotive tool that allows the ignition switch to be bypassed for cranking the engine.
Remote system
Refrigerating system in which condensing unit is away from space to be cooled.
Removable rim
The act of taking a component off a basic unit with the intention of disassembly or replacement.
A chemical or compound used to clear away unwanted material.

RenaultClick image for books on

A vehicle brand of which the following models with required application are classic cars:

  • 1925-28 45 HP (40 CV)
  • 1929-34 40 hp (41CV) Reinastella and Reinasport
  • 1930-39 Nervahuit, Nervastella, Nervasport, and Suprastella 8 cylinder
A model of automobile manufactured by Buick Division of General Motors from 2002-07
Renewable Energy
Energy obtained from sources that are essentially inexhaustible, unlike fossil fuels. It includes conventional hydro-electric, wood, bio-feedstocks, waste, geothermal, wind, photovoltaic, and solar thermal energy.
A vehicle brand of which the following models are classic cars:

  • 1931-33 Royale 8-31, Royale 8-35, Royale 8-52, and Royale Custom 8
  • 1934 N1, N2, and 8-52
To restore something to working condition, e.g., by reconditioning, rebuilding, or replacing.

Repair and Service Council
Repairers Association
Repair gum
Repair kit
A package of the parts needed to repair a particular component (e.g., carburetor, generator, pump, universal joint, etc.).
Repair link
A link in some motorcycle and bicycle chains that can be easily disassembled for chain repair
Repair manual
A book which details the procedure for repairing one or more components of a vehicle. Compare Service manual.
Repair section
A special panel supplied for body repairs that does not include the full panel used for assembling the car but only the most vulnerable areas; i.e., for fenders, separate repair sections are supplied for the headlight area and the bottom fender edges, where damage usually occurs. Compare Replacement panel.
Repair shop
Repeater lamp
A British term for a signal light on the side of a vehicle.
Replaceable derailleur hanger
A type of derailleur hanger that can be easily replaced using hand tools if it gets damaged
Replacement market
All products and services used in the repair and maintenance of vehicles.
Replacement panel
A body panel supplied for repair purposes; sometimes also used to denote a repair section.
Replacement vehicle
  1. A car loaned by a dealer to a customer while the customer’s car is under repair.
  2. A vehicle which is acquired in order to take the place of a vehicle which is being retired from service. These acquisitions do not increase the size of the company fleet.
Replenishing port
  1. An opening in the master cylinder body which connects the fluid reservoir to the Annulus of the primary piston. Compare Compensating port. In a tandem master cylinder, there is one replenishing port for each piston. It is the first port as seen from the pushrod end of the master cylinder and it is always open. Also called a Breather port
  2. Breather port
  3. The opening between the fluid reservoir and the low-pressure chamber that keeps the chamber filled with fluid.
Replica panel
Hard-edged sportbikes. These motorcycle are characterized by riding positions that tuck the rider into an extreme crouch, forcing him to practically lay down on the fuel tank
A colloquial term for a car used by a sales representative.
Reporting Standards
Abbreviation for Reproduction
Parts or complete vehicles that have been manufactured to closely follow or exceed original Specifications, materials, and performance. Also called repro or repros. These parts often are so perfect that not even a Concours judge can tell that they are not NOS or OEM.
Reproduction panel
Repulsion-start induction motor
An electric motor type which has an electrical winding on the rotor for starting purposes.
Required ignition voltage
The maximum high voltage required to produce a spark under particular conditions.
  1. An abbreviation for resume on a cruise control switch which sets the cruise speed back to what it was after being shut off.
  2. A Ballast resistor.
Research & development
(R&D) Basic and applied research in the sciences and engineering and the design and development of prototypes and processes, excluding quality control, routine product testing, market research, sales promotion, sales service, research in the social sciences or psychology, and other non-technological activities or technical services.
Research and Experimental Development Program
Research octane number

  1. A fuel octane rating determined by the research octane test
  2. The octane as tested in a single-cylinder octane test engine operated under less severe operating conditions. RON affects low- to medium-speed knock and engine run-on. Research Octane is presented by the designation R in the (R+M)/2 equation and is the higher of the two numbers.
To recut a valve seat after repeated grinding-in has worn it out of shape.
  1. The amount left in the fuel tank. On many motorcycles there is no gas gauge. Instead, the fuel tap has two settings. The regular setting allows most of the fuel to be used. When this amount is finished, the fuel tap can be adjusted so that the remaining portion can be used. During this time, it is wise to fill up the tank.
  2. A kickback the bank gives the dealer for setting up the loan. The income a dealership realized on a contract in excess of the finance source’s discount rate. For example: If the bank is going to charge $600.00 in finance charges on a given contract and the total finance charge to the customer on this contract is $1,000.00, the dealership will realize $400 in reserve money but the customer thinks the interest is all being charged by the bank.
Reserve capacity
The time, in minutes, that a battery can maintain a discharge rate of 25 amps.
  1. Any container filled with fluid.
  2. The space between the outer and inner tubes of a double-tube shock absorber which takes up the oil squeezed out of the working chamber corresponding to the volume of the piston rod immersed in the working chamber.
  3. A container attached to the master cylinder, either directly or by hoses, that stores extra brake fluid for the hydraulic system
Reservoir diaphragm gasket
The gasket under the master cylinder reservoir cap separating the fluid from the atmosphere. Moves with fluid to allow venting above the fluid.
Reset button
A switch which puts the configuration of a component back to its standard setting.
  1. A panel beating process for removing dents the panel is brought roughly into its original shape before detailed work is performed in the finishing stage.
  2. The process of forming a panel from sheet steel.
Residential vehicles
Motorized vehicles used by U.S. households for personal transportation. Excluded are motorcycles, mopeds, large trucks, and buses. Included are automobiles, station wagons, passenger vans, cargo vans, motor homes, pickup trucks, and SUVs or similar vehicles. In order to be included in the EIA survey, vehicles must be (1) owned by members of the household, or (2) company cars not owned by household members but regularly available to household members for their personal use and ordinarily kept at home, or (3) rented or leased for 1 month or more.
The termination value of an automobile that is being leased. The number on the lease contract may be real or simply made up.

Residual brake pressure type check valve
A two-function unit in which one function either restricts fluid from the brake wheel cylinder(s) or retains a pressure in the brake wheel cylinder(s) at the time of brake release, and in which the other function permits fluid compensation for fluid volume changes.

Residual check valve
Residual discount
If the end-of-lease purchase price (stated residual value) is greater than the expected end-of-lease value (expected residual value), the dollar difference represents the value of the vehicle that you will not pay for during the lease.
Residual exhaust gases
The exhaust gas remaining in the cylinder of a two-stroke engine after the exhaust ports have been closed, i.e., these gases have not been scavenged.
Residual Fuel Oil
  1. Heavy fuel oils produced from the non-volatile residue from the fractional distillation process. Heavy oils that are leftovers from various refining processes. Heavy black oils used in marine boilers and in heating plants.
  2. A general classification for the heavier oils, known as No. 5 and No. 6 fuel oils, that remain after the distillate fuel oils and lighter hydrocarbons are distilled away in refinery operations. It conforms to ASTM Specifications D 396 and D 975 and Federal Specification VV-F-815C. No. 5, a residual fuel oil of medium viscosity, is also known as Navy Special and is defined in Military Specification MIL-F-859E, including Amendment 2 (NATO Symbol F-770). It is used in steam-powered vessels in government service and inshore powerplants. No. 6 fuel oil includes Bunker C fuel oil and is used for the production of electric power, space heating, vessel bunkering, and various industrial purposes.
Residual penalty
If the end-of-lease purchase price (stated residual value) is less than the expected end-of-lease value (expected residual value), the dollar difference represents the additional value of the vehicle you’ll pay for during the lease.
Residual pressure
  1. Fuel pressure maintained within the system after engine shutdown.
  2. Pressure remaining in a hydraulic circuit after the brakes have been released
Residual pressure check valve
A small valve, usually located in the outlet port(s) of the master cylinder, which maintains a certain amount of positive pressure in the hydraulic circuit(s) when the brakes are released.
Residual pressure valve
A valve mounted in the cylinder outlet between piston and brake lines of drum brake circuits. It maintains a certain minimum pressure in the system. Disc brakes do not require a residual pressure valve.
Residual value
Residue gas
Natural gas from which natural gas processing plant liquid products and, in some cases, nonhydrocarbon components have been extracted.
Residue from crude oil after distilling off all but the heaviest components, with a boiling range greater than 538°C.
Capability of a sealer or coating to return to is original size and shape after deformation
Resilient mounting
A suspension system or cushioned mounting designed to reduce the transmission of normal electric motor noise and vibration to the mounting surface
  1. A secretion from trees used in Varnishes, printing ink, and plastic as a binder.
  2. A synthetic product with some of the same physical properties as the plant secretion.
  3. A liquid plastic used in body work.
  4. Synthetic plastic adhesive.
A substance applied onto aluminum pieces before etching; no surface particles are removed where the surface is covered with the protective coating.
  1. An opposing force.
  2. A measure of a conductor’s ability to retard the flow of electricity.
  3. An opposition to flow or movement; a coefficient of friction.
  4. (R) The degree of obstacle presented by a material to the flow of electrical current. Resistance is measured in ohms. R is the symbol
Resistance, electrical
The difficulty electrons have moving through a conductor or substance.
Resistance Loss
Resistance shrinking
Ripples in the bodywork are removed by shrinking the panel with the aid of heat from an electric current provided by the electrode of a special tool which is brought into contact with the rippled area.
Resistance test
Resistance thermometer
An electrical temperature sensor which, in contrast to a thermocouple, needs an external voltage supply; the actual sensing element is a resistor whose resistance is an accurate indication of the temperature.
Resistance welding
Fusing metals using the resistance of the metals to the flow of electricity, as the source of heat.
The ability of a material not to conduct electricity. The opposite is Conductivity.
  1. A device placed in a circuit to lower the voltage. It will also decrease the flow of current.
  2. Electrical device that is a poor conductor of electricity and produces a given amount of resistance to current flow.
  3. An electronic device that reduces voltage to regulate an electric motor.
Resistor spark plug
A spark plug containing a Resistor designed to shorten both the capacitive and inductive phases of the spark. This will suppress radio interference and lengthen electrode life. Using a non-resistor spark plug may also damage a CDI box.

This is a term used of the piston cylinders. The old cylinder Inserts are completely removed and new inserts or sleeves are pressed in. This action is done when the cylinder cannot be rebored.

  1. A small muffler-like device that is placed into the exhaust system near the end of the Tail pipe. It is used to provide additional silencing of the exhaust.
  2. Any device that attenuates pressure spikes.
Resource Conservation and Recovery Act
Federal act that covers businesses that generate, transport, or manage hazardous wastes.
Resources Board
Respirable Combustible Dust
(RCD) A method of measuring ambient DPM exposures using a combustion process. Also used in underground mines in Canada.
Any activity to plow, sand, or otherwise remove snow and ice or reduce hazardous conditions due to snow and ice

To add one or more coats of paint to the existing finish.

The act of working on a vehicle with such care as to bring it back to its Original condition (including original parts, paint, chroming processes, etc.) rather than merely Rebuilding or repairing one.

A term coined by Mark A. Rock of Columbia Station, OH. A quasi-disease which affects a person with a restorable vehicle so that he feels compelled to work on his vehicle rather than eat, sleep, or anything else. While working on his vehicle to repair or replace a particular part, the disease compels him to disassemble, clean, polish, repair, etc. everything associated with the initial part and he justifies his actions by saying, ‘While I am at it, I might as well do it right.’

A device used to halt the movement of something.

Restraint Agreement
Restraint inflatable air-bag system
Restraint system
A general term for occupant safety systems such as seat belts, belt tensioners, air bags, child seats, etc.

  1. A porous device located in vacuum lines to delay vacuum applied to diaphragms.
  2. A device for producing a deliberate pressure drop or resistance in a line by reducing the cross-sectional flow area.
Restrictor plate
A plate attached to the carburetor that limits the amount of airflow entering the combustion chamber. It decreases horsepower.
Rest stop
A place at the side of a road where drivers can stop (to rest). TheBritish term is ‘lay-by’.
Trucker slang for a roadside rest area as in ‘Can anyone tell me where the next eastbound rest-em-up is?’
A switch on the cruise control system. If you are driving on cruise control, for example at 100 kph, and approach some slow traffic, you would normally apply the brakes. This action will disengage the cruise control and allow you to slow down. Once you are past the slow traffic, you can go back to the speed you had previously set by simply hitting the ‘resume’ button. The vehicle will accelerate to that speed.
  1. If the cylinder head is warped due to thermal differences, its mating surface will have to be machined to ensure first that a level surface is created and second that the engine’s compression ratio is not increased above a tolerable value.
  2. The process of machining a brake drum or disc on a brake lathe to remove surface imperfections from the friction surface. Resurfacing is also done after a rotor is turned to give the friction surfaces a non-directional finish.
  3. The addition of a layer or layers of paving material to provide additional structural integrity, improve serviceability, and rideability.
The price of something that the customer pays (in contrast with wholesale).

An organization that sells gasoline to end-users or consumers.
Retail motor gasoline prices
Motor gasoline prices calculated each month by the Bureau of Labor Statistics (BLS) in conjunction with the construction of the Consumer Price Index.
Retail price
A device which holds something in place.

Retainer pin
Retainer plate
A plate which prevents a valve from sliding out of its bore.
Retainer spring tool
A special automotive tool used on drum brakes for restraining the shoe retaining springs for removal and installation. It comes in a variety of shapes, e.g., as a screwdriver-type tool with a special socket end to grip retaining washers.
Retaining key
A metal plate used to secure some sliding calipers in their anchor plates.
Retaining ring
Retaining spring
A spring used to connect the lower ends of a pair of brake shoes and to hold them in contact with the star wheel adjuster.
Retaining wall
A concrete, wood, or block wall designed to hold back slopes.
  1. To set the ignition timing so that a spark occurs later or less degrees before TDC. It involves adjusting the camshaft, distributor spark, or valve operation. In this way, the spark plugs fire or the valves open later in the cycle.
  2. The device for doing this action.
  3. The opposite of advance.
Retard Delay Valve
Occurring late.
  1. An additive to decrease the evaporation rate of a thinner or reducer in paint; used to improve viscosity in hot weather.
  2. A substance which slows down the chemical process of something. Compare accelerator
  3. An auxiliary brake used on commercial vehicles and coaches (it is a requirement in some European countries).
    • The most common type is called a Jake Brake because the predominant manufacturer is Jacobs Vehicle Equipment Co.
    • Other types of retarders include exhaust retarders, transmission-mounted hydraulic retarders and axle-mounted electromagnetic retarders.
    • Also called
Retard unit
Retire from service
A vehicle is retired from service if that vehicle is placed out of service and there are no future plans to return that vehicle to service.
To draw back, pull back, or rewind.
Retractable aerial
A telescopic aerial or Power antenna.
Retractable antenna
Retractable headlights
Also called hideaway headlights

Retracting spring
Used to pull the brake shoes away from the drum when the brake pedal is released. Also pushes the wheel cylinder piston back into its bore, returning the brake fluid to the master cylinder.
A seat belt device which locks the reel of a seat belt when the forward acceleration of the occupants exceeds a certain value.

Retractor indicator lamp
  1. A means of extending the life of a tire that has worn its original tread, yet still has a sound carcass. The Casing is prepared by buffing off tread rubber and vulcanizing new tread rubber stock in its place.
  2. A casing to which tread rubber has been affixed to extend the useable life of the tire after the original tread has been worn out.
  3. The term in some parts of the USA and Australia is recap.

Retread shop
  1. To equip a vehicle with new parts after it has been manufactured.
  2. To rework an older installation to bring it up to date with modern equipment or to meet new code requirements.
Return air
Air removed from a space and recirculated or exhausted.
Return line
Return Mechanism
Return spring
  1. A spring which is attached to a lever so that when the lever is moved in one direction, the spring forces it back.
  2. Springs used on drum brakes to pull the brake shoes away from the drums when the brakes are released
Return sweep
A body panel section presenting a concave appearance; its most common function is to strengthen loose panel areas such as the finish along the wheel aperture of the fender.
Abbreviation for Revolution.
Rev counter
A colloquial term for Tachometer.
A vehicle brand of which the 1925-1948 models are classic cars.
  1. To drive backward or to back up.
  2. Reverse gear (R).
Reverse bias
Nonconductive condition that exists when current flow is blocked by a diode.
Reverse bleeding
A method of purging air from a hydraulic system by forcing fluid into the system at a bleeder valve and allowing the air to escape at the master cylinder.
Reverse brake shoe
Reverse clutch
A clutch which couples the components of planetary gear sets or trains in such a way that the vehicle can be driven backwards.
Reverse curve panel hammer
Reverse curve panel hammerReverse curve panel hammer

A specialized hammer used in repairing damaged body work

Reverse cycle defrost
Method of heating evaporator for defrosting. Valves move hot gas from compressor into evaporator.
Reversed Elliot axle
An axle design in which the axle beam terminates in an eye, the steering knuckle axis dividing as a yoke or fork-shaped end which straddles the axle beam end.
Reversed polarity
(Electrode positive-anode) referring to DC and causing electrons to flow from the base metal to the electrode.
Reverse Elliot steering knuckle
Type of axle construction in which steering spindle straddles ends of axle beam.
Reverse-Elliot type axle
A solid bar front axle on which the steering knuckles span or straddle the axle ends.
Reverse-flow scavenging
A scavenging system for two-stroke engines in which a cylinder has two pairs of transfer ports, at the front and rear respectively, with two exhaust ports located on either side of the two pairs of transfer ports; the incoming streams of mixture spread out like a fan, are deflected downward and expel the spent gases.
Reverse flush
Cleaning the cooling system by pumping a powerful cleaning agent through the system in a direction opposite to that of normal flow.
Reverse gear
A very low gear for driving backwards, denoted by the letter R on a gear knob or gear selector.
Reverse idler gear
A gear used in the transmission to produce a reverse rotation of the transmission Output shaft.
Reverse inhibitor valve
A valve which prevents the engagement of the reverse clutch in an automatic transmissions if the vehicle road speed exceeds 10 kph (6 mph).
Reverse lock
A steering condition where the front wheels are pointed in the opposite (reverse) direction of the turn. This technique is used in a rear wheel skid.
Reverse process
An immersion or combined spray/immersion process employed to apply two protective coatings which, in the case of body shells, replace the dip primer coat and the filler coat. The designation derives from the fact that the sequence in which the dip primer coat and the filler coat are applied is reversed. Compare Electrostatic powder coating.
Reverse scavenging
Reverse shoe
Reverse thread
A common name for Left-hand thread
Reversible fuel cell
A type of fuel cell in which the chemical reactants undergo reversible reactions, such that the cell may be recharged with a separate power source if desired. For example, the hydrogen/oxygen fuel cell may be recharged by providing power for water electrolysis with hydrogen storage. Also called a Regenerative Fuel Cell.
Reversible gear puller
A puller with two or more reversible jaws, allowing it to be used for inside and outside pulling.
Reversing light
A British term for Back-up light.
Reversing valve
Device used to reverse direction of the refrigerant flow, depending upon whether heating or cooling is desired.
Reversing warning signal
British term for Backup alarm.
Excessive heating of a cured rubber compound leading to deterioration of its physical properties.
Rev limiter
One complete turn around an axis
Revolution counter
  1. A tachometer, which measures the engine speed in rpm.
  2. A counter which counts the total revolutions of a shaft as opposed to rpm.
Revolutions per kilometre
(RPK) A measurement of the number of times a tire turns in one kilometre of travel.
Revolutions per mile
(RPM) A measurement of the number of times a tire turns in one mile of travel.
Revolutions per minute
(RPM) The speed the engine crankshaft is turning.


Rev range
Automotive jargon for the range of speeds (expressed as revolutions per minute) in which an engine is designed to operate. The lowest point in the rev range is the idle speed; the highest point is the redline.
  1. To increase the speed of an engine.
  2. The number of revolutions per minute.
Reynolds numbers
A numerical ratio of the dynamic forces of mass flow to the sheer stress due to viscosity.
Abbreviation for Reformulated Gasoline — gasoline blended with pollution reducing additives
Abbreviation for Radio frequency interference.
RFI suppressed spark plugs
Fully shielded and resistor spark plugs.
  1. Abbreviation for right hand, as in RH drive. For all vehicles, left and right are from the perspective of sitting in the forward-facing Driver’s seat.
  2. Abbreviation for Relative humidity.
Abbreviation for Reactive hydrocarbons
Abbreviation for right-hand drive.
  1. A resistor with variable resistance, e.g., the switch that dims the instrument panel lights.
  2. A variable resistor used to control blower speeds.
A silver-white noble metal in the platinum family; atomic number 45, atomic weight 102.905; used in thermocouples and, together with other platinum metals, as a catalyst in catalytic converters.
Abbreviation for Rear head restraints.
  1. The continuous raised portions of rubber that run circumferentially (straight or in a zigzag pattern) making up the tread on the tire. Also the term applies to various raised surfaces circling the sidewall, i.e., guide rib.
  2. A structural member for reinforcing bodywork.
Ribbed Neck Carriage Bolt
A plain, circular, oval head bolt with a serrated neck to prevent rotation.
  1. A series of raised portions in castings or moldings to increase rigidity.
  2. A narrow recess stamped into relatively flat body panels, e.g., floorpans, that helps to reinforce the panel and to suppress vibrations in it.
Ribbon silicon
Crystalline silicon that is used in photovoltaic cells. Ribbon silicon is fabricated by a variety of solidification (crystallization) methods that withdraw thin silicon sheets from pools of relatively pure molten silicon.
Ricardo principle
An arrangement in which a portion of the combustion chamber came in very close contact with the Piston head. The other portion, off to one side, contained more space. As the piston neared TDC on the compression stroke, the fuel mixture was squeezed tightly between the piston and head thus causing the mixture to squirt outward into the larger area in a very turbulent manner. This produced a superior mixture and allowed Compression ratios to be raised without Detonation.
An air/fuel mixture that has more petrol than normal. The opposite is lean.
Rich air-fuel mixture
A mixture of air and fuel in which there is less air and more fuel.

Rich mixture
A mixture of air and fuel in which there is less air and more fuel. The opposite is lean mixture. A slightly rich mixture generates the maximum achievable engine power, an overly rich mixture causes spark plug fouling, loss of engine power, and excessive fuel consumption. Any rich mixture increases exhaust emissions.

The degree of comfort, especially with regard to the suspension, experienced by the passengers.

Ride control
Ride height
A measurement between the ground and some fixed reference point on a car’s body. The exact location of the fixed point varies among manufacturers. This dimension can be used to measure the amount of suspension deflection or the height of the body from the ground.

Ride-height adjuster
Ride leveling
  1. A person who operates a motorcycle.
  2. A passenger (but generally not the driver) of a car or truck.
  3. A vehicle.
  4. A clause in a contract
Ride steer
A generally undesirable condition in which a wheel steers slightly as its suspension compresses or extends. Also called bump steer.
Ride Suspension
  1. An edge, ledge, or lip which protrudes beyond the normal face of an object.
  2. The cutting edge of a screw thread above the flanks.
  3. A Hump.
Riding the clutch
A situation where the driver rests his foot on the Clutch pedal while the vehicle is being driven. This action can cause undue wear on the clutch plates because they may be rubbing against each other ever so slightly.
Riding two up
Carrying a passenger on your bike.
A large truck.

When referring to the side of a unit, the right side is always from the perspective of operation. In other words, when sitting in the driver’s seat or when riding a bicycle or when pushing a mower, the right side is the operator’s right hand side. In other words the left or right side is determined by facing the rear of the unit.
Right-hand drive
(RHD) A steering system in which the steering wheel is located on the right-hand side of the vehicle; used for driving on the left, as in the UK, Japan, Australia, etc. The opposite is Left-hand drive.
Right hand thread
Right-hand thread
  1. The common direction (clockwise) which is used to secure a nut to a bolt.
  2. A thread is a right hand thread if, when viewed axially, it winds in a clockwise and receding direction.
Right hand turn signal
Right Hand Turn SignalRight Hand Turn Signal

A device which is attached to the turn signal lever on the left side of the steering wheel to allow disabled people to operate the turn signals from the right side.

(ROW) Land, property or property interest, usually in a strip, acquired for or devoted to transportation or other public works purposes. Includes the roadbed, ditches, road slopes, back slopes, bridges, trestles, or other structures, acquired for or devoted to transportation purposes. This does not include recreational or nature trails except where they intersect with or are located within road rights-of-way.
Right turn sign
Right turn signRight turn sign

A traffic sign indicating that the road makes a sharp turn to the right

Inflexible, without any flexural or elastic characteristic.
Rigid axle
A simple non-independent suspension, consisting of a rigid transverse member with wheel hubs solidly bolted to it. The axle can be attached to the body by Leaf springs, or by a combination of suspension arms and links. A rear axle which may be either live (in rearwheel drive cars) or dead (in front-wheel drive cars).
Rigid axle connection
Fixed drive.
RileyClick image for books on

An automobile manufactured by British Leyland. The 1925-1948 models with required application are classic cars. The 1945-55 2.5 (RMA, RME) models are milestone cars.

  1. The outer edge of a dented area in a body panel that is heat shrunk towards the center of the dent.
  2. On a bicycle, the metal or wooden hoop of a wheel that holds the tire and tube and the outer ends of the spokes.
  3. On a truck, the metal assembly consisting of a base and either a side ring or a side and lock ring combination, which are removable from one side for tire mounting. The opposite side has a fixed flange to retain the tire. Note Passenger and tubeless rims do not have removable side and lock rings.
Abbreviation for Reaction injection molding.
Rim bead seat
The portion of the wheel rim below the rim flange providing radial support to the bead of the tire.
Rim bead seat taper
The narrowing of the rim width towards the rim well. The taper must be designed to lock the tire to the rim and provide a good seal; well-base rims for passenger cars have a 5° taper, those for commercial vehicles have a 15° taper; flat base rims for commercial vehicles have no taper.
Rim brake
Any type of brake that slows or stops a wheel by pressing its pads against the sides of the wheel Rim.
Rim designation
The nominal rim diameter, nominal rim width and any abbreviations and codes for the contour of the rim.

Rim diameter
The distance between the intersection of the bead seats and the vertical walls of the rim flanges.

Rim drivers
Riveted or welded metal blocks or extrusions on both sides of the valve slot to prevent valve damage due to rim slippage on cast spokes.
Rim flange
The part of a rim that supports the tire bead in a lateral direction; the linear distance between the two rim flanges is termed rim width.
Rim offset
A measurement in inches from the center of the rim (between the flanges) to the tip of the 28° gutter bevel.
Rim pull
Actual amount of effort in pounds available at the point of contact of tire and road surface.
Rim ridge

Rim size
The dimension of a wheel covering the rim width and rim diameter and is measured in inches.
Rim steering wheel
Rim strip
A thin, narrow strip of material (usually rubber or cloth) placed around the outside of a rim (beneath the tube) to cover the sharp edges of the spoke which might protrude beyond the nipple.


Rim tape
A rubber strap which covers the spoke nipples on the inside of the rim to protect the spoke from poking into the tube.
Rim taper
The slope of the rim.

Rim type
Depending on the type of tire, rim types differ according to the rim profile and the number of rim parts. Compare Multi-piece rim, One-piece rim, and Safety rim.
Rim well
The portion of the rim with a substantially smaller diameter than the bead seats and located with sufficient depth and width to enable the tire beads to be forced over the mounting side of the rim flange and bead seat taper for installation or removal.
Rim well base
The portion of the rim with a substantially smaller diameter than the bead seats and located with sufficient depth and width to enable the tire beads to be forced over the mounting side of the rim flange and bead seat taper for installation or removal.
Rim width
The nominal distance between the rim flanges. The width of a rim is an important factor in the handling characteristics of a car a rim that is too narrow in relation to the tire width will cause the tire to distort sideways under fast cornering. Unduly wide rims on an ordinary car tend to give a rather harsh ride because the sidewalls of the tire have insufficient curvature to make them flex properly over irregularities in the road.

A circular piece or band of metal.

Ring and pinion
Ring and PinionRing and Pinion

A term used to describe the differential Drive pinion and Ring gear.

Ring belt
The lands and rings of a piston.
An iron bolt having a ring through an eye at one end, through which a rope can be passed and tied.
Ring clamp
Ring end gap
Ring expander
Ring flutter
Ring gap
The space between the piston ring ends with the piston when installed in the bore.

Ring gear
Ring GearRing Gear

  1. The large bevel, circular gear which is attached to the Flange or Carrier of the Differential case. It meshes with the Drive pinion on the end of the Propeller shaft.
  2. The outer gear in a Planetary gearset.
  3. Annular gear.
  4. A toothed rim of a flywheel which engages the pinion of the starter motor.
Ring groove
Ring groove cleaner
Ring groove insert
Ring job
Ring joint
The connection of compression rings in a cylinder: Angle joint, Butt joint, or Lap joint.
Ringlemann scale
Device for measuring smoke density.
Ring pliers
Ring ridge
Ring side clearance
Ring spanner
A British term for a Box wrench.
Ring stop
Ring wrench
Rinse treatment
Ripping hammer
A hammer which looks like a claw hammer, but the claw is straight.
Ripple current
The undesirable AC (ripple) component of a pulsating DC current produced by a rectifier or similar power conditioning device.
Erosion resistant cover material (including rock or large aggregate) for protecting slopes, basins, streambanks, bridge abutments, or other erodible sites from runoff or wave action.
Riser bars
A mountain bike handlebar that features an upward sweep providing a more upright riding position and greater stability.
Riser valve
Device used to manually control flow of refrigerant in vertical piping.
Rising rate
A suspension system that becomes harder to compress the farther it is compressed. This is usually achieved by a mechanical linkage with variable leverage ratio.
Rising rate suspension
Rising-rate suspension
A Suspension system where the spring rate increases when the wheels move further into Jounce. This action can be accomplished by configuring the geometric shape of the suspension, by using springs which change tension as they are compressed, or by using two or more springs with rubber stops. The purpose of a rising-rate suspension is to maintain consistent ride and handling characteristics under a variety of situations loaded or unloaded, straight roads or curves, and smooth roads or bumpy.
  1. A metal pin used to hold two objects together. One end of the pin has a head and the other end must be set or Peened over to create another head
  2. A semipermanent fastener used to hold two pieces together.
  3. A headed metal fastener of some malleable material used to join parts, as metal plates, of structures and machines by inserting the shank through a hole in each piece and forming a head on the headless end.
Rivet Bolt
A bolt designed as a substitute for rivets, having a button head, a ribbed shank, a UNC thread, or a special thread such as a Dardalet thread or Lok-ThreadTM
Riveted brake lining
A brake shoe that is attached to the backing plate with rivets rather than glued on.
Riveted linings
Brake linings that are riveted to the pad backing plate or brake shoe with copper or aluminum rivets.
A tool with pliers-like handles and nose piece to insert rivets. It is used, for example, in body repair work to rivet sheet metal material together.
Rivet gun
A tool with pliers-like handles and nose piece to insert rivets. It is used, for example, in body repair work to rivet sheet metal material together.
Riveting hammer
A hammer with a special head for securing rivets.
Buick RivieraClick image for books on
Buick Riviera

A model name of several generations of automobile manufactured by Buick division of General Motors (1949-50, 1963-65, 1966-70, 1971-73, 1974-76, 1977-78, 1979-85, 1986-93, 1995-1999). The Riviera for 1949 and 1963-70 are milestone cars. Buick also used the name for concept cars.


A one-piece internally threaded and counterbored tubular aluminum rivet that can be pulled up or headed while working entirely from one side, forming a bulge or head on the blind side. This upset is large enough to resist being pulled through metal or plastic even under conditions of eccentric load. It overcomes the difficulty of installing brackets, handles or other attachments to tubular pieces.


Abbreviation for Remote Keyless Entry

Refers to Red line tires which were marketed in the late ’60s and early 70s.
Abbreviation for a Reflector lamp
Abbreviation for Relay Module
Abbreviation for Rubber Manufactures Association.
abbreviation for root-mean-square
Any large path upon which vehicles travel.

In highway construction, the graded portion of a highway within top and side slopes, prepared as a foundation for the pavement structure and shoulder.
Road closure
An action by the authorities to stop vehicles from using a road. It is usually done when there has been a serious accident blocking the road or when the road conditions are bad (such as snow storms, earthquakes, avalanches, etc.).
Road construction
Road Construction signRoad Construction sign

Improvements made to the road surface. When passing construction sites, speed limits are greatly reduced. In many locations fines are doubled in construction zones

Road Construction Signage
Every road and bridge construction project must use signage to alert motorists of the construction ahead. Construction signage is usually orange with black lettering, sometimes with flashing yellow lights. Road construction requires motorists to slow down, so watch for alternate speed limits imposed on road and bridge construction projects. It is common to see signs that fines double in construction zones.
Road course
A closed course with turns to both the right and the left mimicking a normal road.
Road-draft tube
British term for Oil breather pipe or Oil breather tube.
Road feel
The impression imparted to the driver through the steering wheel by the wheels of a vehicle in motion. This feeling can be very important in sensing and predetermining vehicle steering response.
Road fund license
A British license showing that road tax has been paid.
Road hazard
Injury to a tire sustained in normal operation, excluding collision or vandalism and that is not reparable by accepted standards.
Road hog
A selfish, often aggressive driver.
Road holding
The ability of a vehicle to grip the pavement. Technically described as lateral acceleration, because cornering is actually a continuous deviation from a straight path. Measured in g’s.
A bicycle rider who prefers riding on paved surfaces.
Road load horsepower
The amount of power at the driving wheels needed to move a vehicle down the road at a steady speed. This power varies according to the vehicle’s speed, aerodynamic drag, mechanical friction, and the tires’ rolling Resistance. Road-load horsepower is distinct from engine power because the output of the engine is sapped by various mechanical losses between the engine’s output at its flywheel and the driving wheels.
A model of automobile manufactured by Buick Division of General Motors from 1936-1958, 1991-1996
Road oil
Any heavy petroleum oil, including residual asphaltic oil used as a dust pallative and surface treatment on roads and highways. It is generally produced in six grades, from 0, the most liquid, to 5, the most viscous.
Road rage
The violent behavior by a driver which may be precipitated by being cut off, forgetting to signal, getting an insulting gesture, or other forms of aggressive driving. A deliberate and violent act against another driver and is a criminal offense.
Semitrailer designed to travel both on highway and on rails. Manufactured by Wabash National Corporation.
Road rash
Any type of bruise or wound that is inflicted when you hit the ground, generally in a low-speed crash. A skinned knee is a type of road rash; multiply that by 100 and you get road rash that happens to unprotected motorcycle riders during an accident. High-speed crashes do much more damage.
Roadside Assistance
A service available from General Motors, during the warranty period, to assist you whenever a problem may occur (e.g. lock-out assistance, a jump start, flat tire change, fuel delivery or towing assistance).
Roadside turnout
A wide area to the side of the road to permit you to park your car so you can make repairs, change drivers, or empty garbage (when there is a large garbage can supplied).
Road speed
A vehicle’s speed along a road, measured in mph or kph.
(Rdstr) This term derives from equestrian vocabulary where it was applied to a horse used for riding on the roads. A convertible is an open car with windows; a roadster is an open car without windows. Old dictionaries define the roadster as an open-type car designed for use on ordinary roads, with a single seat for two persons and, often, a rumble seat. It is an open-type body with one bench seat and a luggage compartment in the rear deck. The weatherproof fabric top may be folded, and side curtains may be removed. The windshield usually may be folded down. The original concept is maintained by the Morgan Plus 8 but modern roadsters include power features such as power steering, electric windows, etc. as in the Mercedes-Benz SL.

Road surfaces
Road tax
An annual tax paid in order to use a vehicle on the roads.
Road test
  1. A test to check that a car is roadworthy after repair.
  2. A test of a car (e.g., a new model) in actual use; for example, by a magazine for comparison with other models.
  3. An examination of a driver’s ability and skill to operate a vehicle within the parameters of a licensing agency. Usually administered after the candidate has passed a written test proving his knowledge of the rules of the road
To give a vehicle a Road test.
Road tire
A bicycle tire that is usually 700C or 27 in. sizes with a non-aggressive tread.
Road train
Several linked trailers pulled by a large truck; common in Australia for transporting stock.
That part of the road designed and used for vehicular travel. It does not include the median, berm, or shoulder.
Road Weather Information Systems
(RWIS) Provides real-time atmospheric weather data, pavement temperature and surface conditions. Links to weather forecasts, weather warnings, and radar and satellite images.
Road wheel
A bicycle wheel consists of a hub, rim, and spokes. Modern road wheels are generally size 700C. Older road bike wheels may be 27 in.
A vehicle which is fit to be driven on the roads.
A mechanically sound vehicle which is fit to be driven on the roads.
A vehicle brand of which the following models are classic cars:

  • All Rochester-Duesenberg 4-cylinder
  • 1925 6-54E
  • 1925-1929 8-88
  • 1929-1931 8-125
Robertson screw
A screw head, invented by P. L. Robertson, with a recessed square hole. It is more commonly found in Canada than the US, especially in woodworking situations. It is easier to install and remove than a Phillips screw and does not strip the head as easily. There are four basic sizes (measured across the flats) 1.6 mm, 2.0 mm, 2.6 mm, and 3.0 mm.
Robot spraying
The application of paint by robots.
A vehicle brand of which the 1925-1948 models with required application are classic cars.
Rocker arm
A curved lever that pivots in the middle. One end is attached to the top of the Valve stem. In overhead-valve engines the other end is attached to the Pushrod. In some overhead-cam engines the other end is attached directly to the camshaft lobe. As the camshaft rotates, the rocker arms pivot causing the valves to open and close.

Rocker arm cover
A metal lid located on top of the Cylinder head on vehicles that have valves that are activated by an overhead cam or by Rocker arms.

Rocker arm shaft
The shaft upon which the Rocker arms are mounted so that the rocker arms can pivot. Also called rocker shaft.
Rocker Arm Stud
Rocker box
A British term for valve cover (i.e., a cylinder head cover above the valve train).
Rocker cover
A British term for valve cover (i.e., a cylinder head cover above the valve train).
Rocker cover gasket
A British term for Valve cover gasket, (i.e., a gasket between the cylinder head and the valve cover; usually either a flat paper or cork gasket or an O-ring.
Rocker panel
That section of the vehicle body between the front and rear Fenders and beneath the doors. A Sill.
Rocker shaft
  1. The shaft on which the rocker arm pivots
  2. A British term for Cross shaft (i.e., the outgoing shaft of the steering gearbox, to which the pitman arm is connected).
Rocking chair
Trucker slang for vehicle between 2 trucks as in ‘Who we got in the rocking chair tonight.’
Rockwell hardness
A measurement of the degree of hardness of a given substance.
Rockwell Hardness Test
A measure of hardness by determining the depth of penetration of a penetrator into the specimen under certain fixed conditions of test. The penetrator may be either a steel ball or a diamond sphero-conical penetrator. The hardness number is related to the depth of indentation and the higher the number the harder the material.
Rocky Mountain Doubles
A combination vehicle consisting of a tractor pulling a 45 to 48 foot semitrailer and second shorter semitrailer (usually 28 feet in length).
Roc Loc
An adjustable retention system extending off the back of Giro Helmets that allows the helmet to grip the users head better.
  1. A modified car, i.e., Street rod.
  2. To drive a vehicle hard.
  3. A Connecting rod.
  4. To clean out a radiator by passing a rod through the lines by Rodding the radiator.
  5. A thin bar.
Rod arm
Rod bearing
Rodding the radiator
The top and sometimes, the bottom tank of the radiator is removed. The core is then cleaned by passing a cleaning rod down through the tubes. This is done when radiators are quite clogged with rust, Scale, and various mineral deposits.
Rod end
The ends of connecting rods which fit over crank pins or cross head pins.

Rod engine
Rod mounting box
Rod puller
Rod separator
Rod shank
Roger beep
Trucker slang for an add-on device for CB’s that beeps when the mike key is pressed or released as in ‘How much did that roger beep cost ya?’
A vehicle brand of which the 1925-1948 models are classic cars.
The motion of a vehicle in which the springs on one side of the vehicle compress while the springs on the other side extend. If the roll is extensive, the vehicle will fall on its side. Also less accurately called sway or lean, it occurs in corners because the car’s center of gravity is almost always higher than the axis about which it rotates.

Roll angle
The angular displacement of a vehicle about its longitudinal axis, i.e., tendency of a vehicle to tip over when cornering or in high cross winds.
Roll axis
Roll axisRoll axis

The axis through the front and rear roll centers.

Roll back
To work a sales deal backwards. Instead of working with the purchase price and trying to determine a monthly payment, you would start with a known monthly payment and try to determine a selling price. It also means to roll back the odometer on a car to make it worth more money – highly illegal.
A heavy steel bar or tubular steel that goes from one side of the Frame, up and around in back of the Driver in a hoop, and back down to the other side of the Frame. It is used to protect the Driver in the event his vehicle rolls over.

Roll cage
Roll cageRoll cage

A protective structure which surrounds the driver in the event of a rollover or crash. It includes a Rollbar and other bars welded to the rollbar. The roll cage also adds chassis strength and stiffness which makes for better handling characteristics.

Roll center
A term which is used to describe the point around which the body of the vehicle rolls when it corners. If the movement of the vehicle is controlled only by Linkages, the roll center can be discovered by the geometry of the suspension.
Roll coating
An application method for organic or chemical conversion coatings using rolls.
Rolled bead
Rolled Point
The point frequently produced by the cupping of the last 1 to 1 1/2 threads by the thread rolling pressure. This type of point is not produced intentionally but is considered as an alternative form of the plain sheared point.
Rolled thread
Rolled threads are cold formed by squeezing the blank between reciprocating or revolving serrated dies, similar to rolling a pencil between your two hands. This acts to increase the major diameter of the thread over and above the diameter of the unthreaded shank, if any. Rolled threads are both stronger and smoother than cut threads and more economical in so far as the process is faster with no waste of material. Virtually all cold headed fasteners within the Aerospace Industry today have rolled threads.
  1. A device for replacing sliding friction with rolling friction.
  2. While ball bearings use a series of balls in a cage, roller bearings use a series of small cylinders.
  3. A colloquial term for a Rolls-Royce.
Roller bearing
Roller bearingRoller bearing

An anti-friction bearing using a series of straight, cupped, or tapered steel rollers engaging an inner and outer ring or Race.

Roller cage
A metal or plastic enclosure which keeps the rollers in place in a roller bearing.
Rollercam brake
Rollercam brakes
Mountain bike brakes that are attached to the frame posts and use a cam and Pulley system to modify pressure on the rims.
Roller cell pump
Roller chain
A power-transmitting chain in which each link consists of two free-moving rollers located by pins connected to sideplates.

Roller clutch
A clutch, using a series of rollers placed in ramps, that will provide drive power in one direction but will slip or freewheel in the other direction.

Roller Conveyor
A conveyer that uses rollers to move product either by gravity or automation. See Gravity Conveyor
Roller dynamometer
A dynamometer attached to a number of rollers so that the vehicle’s driving wheels are placed on them to simulate road conditions. In this way a vehicle’s actual power to the wheels can be determined.

Roller foot lever
Roller leveling
A process in which steel strips pass rollers which remove excess zinc after the actual immersion process of galvanizing has begun.
Roller lifter
Roller lifters
A stationary training device that consists of a boxlike Frame and three rotating cylinders (one for a bike’s front wheel and two for its rear wheel) on which the Bicycle is balanced and ridden.
Roller seat
Roller seatRoller seat

A mechanic’s stool on wheels

Roller skate
Trucker slang for a small car as in, ‘We got a roller skate broke down in the left lane so watch out.’
Roller tappet
Roller tappets
Valve lifters that have a roller placed on the end contacting the camshaft. This is done to reduce friction between the lobe and lifter. They are generally used when special camshafts and high tension Valve springs have been installed. Also called roller lifters or roller foot levers.
Roller-vane pump
A rotary vane pump with rollers as pumping elements which slide against the pump body when the rotor rotates.


Rolling bearing
Rolling circumference
The circumference of a fully inflated tire under load.
Rolling contact
Rolling friction
A rolling bearing’s frictional resistance to rotation.
Rolling parking lot
Trucker slang for an automobile transport as in ‘Who’s that in the rolling parking lot southbound.’
Rolling radius
The distance from the center of the tire’s ground Contact patch to the center of the wheel rim. It is measured with tire loaded to rated capacity. Used in calculating geared speed.
Rolling resistance
As the wheels begin to turn, there are forces which resist its motion such as low tire pressure, rough road surface, increased tire temperature, tire composition, increased vehicle weight, and even air resistance.
Rolling road
Rollers set in the floor of a service center and designed to simulate road conditions; the rollers can be driven by the driving wheels of a car and connected to a dynamometer for testing the power output of an engine or may be independently powered, e.g., to test the brakes.
Rolling start
A form of race start that begins with the cars already in formation, while also in motion.
Rolling wheel
Roll-Off Container
Typically an open top container designed for transporting solids in bulk, often used as refuse container. The vehicles used for transporting roll-off containers have rails or a flat bed with a hydraulic hoist for loading and unloading these large containers.
Roll oversteer
Oversteer caused by roll when cornering. The opposite is Roll understeer.
Roll pin
A split, tube-like pin made of spring steel for retaining disc pads, gears to shafts in gearboxes, etc.

Roll resistance
Abbreviation for Rolls Royce.

Rolls-RoyceClick image for books on

A vehicle brand of which all models from 1919 to 1948 are classic cars. All the 1947-67 models are milestone cars.

RollsRoyce mascot

Roll steer
A characteristic of handling which gives a slight improvement to steering as the Suspension moves in body roll. Sometimes a bad roll steer occurs when the suspension is poorly designed. A steering effect induced by load transference from side to side. The axles may move out of their normal parallel relationship due to spring deflection.
Roll steer effect
Roll stiffness
The turning moment or torque that the Suspension makes when the body rolls and the suspension tries to pull the body back to its normal upright position. It is usually measured in lb-ft/degree of roll. When the springs are stiffer or when the perpendicular distance from the springs to the Roll center is greater then the roll stiffness increases. As a result, the vehicle corners flatter. Also called roll resistance.
Roll test
An examination of the drive train functions; may include separate tests for front and rear axle, left-hand and right-hand sides, noise test.
Roll threading
Forming threads on a bolt or screw by pushing or rolling the piece through cutting dies. There are two styles of cutting dies:

  • one plate moves and the other is stationary
  • rotating grooved circular rolls
Roll understeer
Understeer caused by roll when cornering. The opposite is Roll oversteer.
Abbreviation for Read Only Memory — memory that contains the computer’s operating instructions (programs). It also stores general information that tells the computer how various components should perform under specific operating condition.
Abbreviation for Research Octane Number

Roo bar
An Australian term for Nerf bar.
Roof air spoiler
Roof air spoilerRoof air spoiler

A spoiler located on the back of the roof of a van

Roof box
An enclosed, multi-purpose roof carrier.
Roof brace
A transverse rail that supports the roof panel; there are usually several roof braces.
Roof panel
The horizontal outer layer of the sheet metal roof panels that is spot-welded along its edges to the top of the roof door and screen pillars.
Roof pillars
The steel pillars that surround the front and rear windshields and front and rear doors in a sedan. Pillars between the windshield and the front door are referred to as A-pillars. Pillars between the front and rear doors are referred to as B-pillars. Pillars between the rear doors and the rear windshield are called C-pillars. They provide greater rigidity to the car and making a hardtop possible.
Roof rack
Roof rackRoof rack

A luggage rack on the roof of a vehicle.

Roof rail
A longitudinal side member above the doors to which the roof panel is attached. Also called ‘cantrail.’
Roof spoiler
A spoiler attached to the roof of a truck cab, or vehicle towing a trailer or motor home, to reduce drag and increase stability.
Room temperature vulcanizing sealer
(RTV) semi-liquid, silicone rubber sealant which is proof against oil and water but not gasoline.
  1. The lowest point of a screw thread.
  2. That surface of the thread which joins the flanks of adjacent thread forms and is identical with or immediately adjacent to the cylinder or cone from which the thread projects.
Root diameter
The minor diameter on screws or the major diameter on nuts.
Roots compressor
A typical lobe-type positive displacement compressor; uses a pair of two-lobed or three-lobed internal rotors phased to prevent clashing of the lobes by gears; normally driven from the crankshaft by toothed or V-belts, can achieve speeds up to 10,000 rpm; provides low-end torque and boost without lag but is less fuel-efficient than a turbocharger.
Roots supercharger
A typical lobe-type positive displacement compressor; uses a pair of two-lobed or three-lobed internal rotors phased to prevent clashing of the lobes by gears; normally driven from the crankshaft by toothed or V-belts, can achieve speeds up to 10,000 rpm; provides low-end torque and boost without lag but is less fuel-efficient than a turbocharger.
RO/RO ship
A cargo or ferry ship on which trucks and other vehicles can be driven on and off on ramps through large openings at the bow, stern or side.
Rosette weld

A circle with streets coming off it like spokes in a wheel. Also called Traffic circle. TheBritish call it a roundabout.
Rotary blade compressor
Mechanism for pumping fluid by revolving blades inside cylindrical housing.
Rotary compressor
  1. A compressor which has rotating rotors, vanes, or eccentric mechanisms that compress and pump refrigerant.
  2. Mechanism which pumps fluid by using rotating motion.
Rotary disc valve
A valve employed as an intake control in modern two-stroke engines, consisting of a thin steel disc attached to one end of the crankshaft. The intake port passes trough to the disc valve assembly, and thus is normally closed off by the disc. To permit induction at the correct part of the engine cycle, part of the disc is cut away, opening the intake port for the required duration, independent of the piston position.
Rotary engine
An internal combustion engine which is not of a Reciprocating (Piston) engine design. There is no true crankshaft, although the power-take-off shaft is sometimes called the crankshaft. It is stationary or fixed in that it simply spins in place. The central rotor turns in one direction only and yet produces the required Intake, Compression, firing and exhaust strokes. Because it uses rotary motion instead of reciprocating motion, the rotary engine has better balance and less vibration than piston engines. Two common rotary engines are the Gas turbine and the Wankel.
Rotary flow
The movement of the oil as it is carried around by the Pump and Turbine in a Torque converter. The rotary motion is not caused by the oil passing through the pump, to turbine, to Stator, etc., as is the case with Vortex flow.Rotary flow is at right angles to the center line of the Converter whereas vortex flow is parallel (more or less depending on the ratio between the speeds of the pump and turbine).
Rotary hammer
A power hammer.
Rotary pump
A pump with rotating members.
Rotary valve
An engine or pump component forming part of a rotating assembly; may be designed as a cylindrical or a disc valve.
Rotary vane pump

Rotate tires
Rotating seal ring
A rotating element of a mechanical seal.
The motion of a body about an axis within the body.

Rotational atomization unit
A painting unit equipped with rapidly rotating spray bells.
A trademark name of an Austrian manufacturer of two-stroke engines used in Ski-Doo® snowmobiles and Sea-Doo® watercraft.
A colloquial term for a vehicle in very poor shape.

Roto cap
A device fitted to some engines which turns a valve slightly every time it opens or closes, to prevent the valve sticking or burning. Also called Valve rotator.
Rotoflex coupling
One design of a flexible coupling in the shape of a hexagonal rubber ring.

A process that removes the top few inches of asphalt in preparation for a new asphalt surface.
  1. Any component which rotates.
  2. A small rotating cap-like unit at the end of the distributor shaft. It is located on the breaker cam inside the cap. It connects between the center electrode and the various outer spark plug terminals as it turns, thus distributing the high voltage from the ignition coil secondary winding to the proper spark plug. Also called rotor arm.
  3. A rotating Armature inside a Stator. As the rotor turns within the stator, electricity is produced to power the electrical components.
  4. The rotating member of an induction motor in a single-phase device. Current that is normally induced in the rotor reacts with the magnetic field produced by the stator. This produces torque and rotation.
  5. A trichoidal device in a rotary engine.
  6. A rotating displacement element of a rotary pump, such as a gear, screw, piston, etc.
  7. A moving part of a pulse generator. The opposite is stator.
  8. A rotating element of a Roots supercharger.
  9. The rotating part of a device, such as a disc-brake rotor.
Rotor arm
Rotor armRotor arm

A small rotating cap-like unit at the end of the distributor shaft. It is located on the breaker cam inside the cap. It connects between the center electrode and the various outer spark plug terminals as it turns, thus distributing the high voltage from the ignition coil secondary winding to the proper spark plug.

Rotor hat
The raised center section of some brake rotors which gives the rotor the shape of a hat.
Rotor Member
Rotor pump
An engine oil pump in which an internal rotor, e.g., with four external lobes, is used to drive an eccentric external gear, e.g., with five internal lobe-spaces; operates in a similar way to gear pumps, but has higher pump capacity, and is quieter and more expensive.

Rotor-type oil pump
Rotor-type oil pumpRotor-type oil pump

An engine oil pump in which an internal rotor, e.g., with four external lobes, is used to drive an eccentric external gear, e.g., with five internal lobe-spaces; operates in a similar way to Gear pumps, but has higher pump capacity, and is quieter and more expensive.

Rotary Injection Pump
A lower-cost injection pump used with pump-line-nozzle systems. The pump has a central plunger system (usually consisting of two opposing plungers) that provides fuel to every cylinder during the required injection period. A plate located near the top of the pump rotates, opening an appropriate orifice at the right time for distribution to each cylinder’s injection nozzle through a separate line. It is usually used with automotive or agricultural engines that have lower performance and durability requirements than the heavy-duty truck diesels.
Rotten-egg smell
In cars equipped with catalytic converters, this smell is the result of an excessively rich air/fuel mixture.
The sound or condition of an engine which is running unevenly.
A mechanical or chemical treatment of a surface to produce minute irregularities.
Roughing dolly
A curved block of cast iron for shaping panels. Since it weighs about 2 kg (4-1/2 lb), it can be used as light weight sledge, yet it is heavy enough to be used in most autobody applications. It is U-shaped to provide a variety of surfaces that can be used as a dolly or a hammer. One edge is formed so it can be used for forming a bead on a fender.
Roughing stone
A coarse stone used for quick removal of material during honing.
A British term for a Traffic circle.
Round file
A file in the shape of a round bar, rather than a blade.
Round Head
Semi-elliptical top surface and flat bearing surface.
Round head bolt
A general term including carriage bolts, cup head bolts, and mushroom head bolts.
Roundhead machine screw
Roundhead machine screwRoundhead machine screw

A machine screw where the base of the head is flat to fit flush with the surface of the material and the top of the head is dome shaped.

Round hump
A safety contour on both rim bead seats preventing the tire from sliding into the rim well.

  1. The direction or path that wiring or a cable takes.
  2. To feed wiring or cable into a certain direction or path.
  3. The roadway that a vehicle takes from one point to another.
RoverClick image for books on

A model of automobile manufactured in the UK

Royal Automobile Club
(RAC) A motoring organization in the UK.
A model of automobile manufactured by Buick Division of General Motors from 2005
Royce mascot
Abbreviation for revolutions per kilometre in measuring the number of times a tire turns in one kilometre of travel.
  1. Abbreviation for revolutions per minute. The number of times a rotating object turns every minute. For instance, a Tachometer measures the number of times the crankshaft of an engine makes one complete rotation every minute and registers the value in terms of rpm.
  2. Abbreviation for revolutions per mile in measuring the number of times a tire turns in one mile of travel.
Rpm sensor
Abbreviation for regular production option — the options installed at the factory as opposed to options installed by the dealer.
Abbreviation for Reinforced reaction injection molding.
Abbreviation for Rural Roads Operations and Maintenance Advisory Committee
Abbreviation for Variable Reluctance Sensor
  1. Abbreviation for Rally Sport; a term used to identify some Chevrolet Camaro models.
  2. Abbreviation for rumble seat.
Abbreviation for relative standard error
Abbreviation for rear seat.
RSXClick logo for books on

A model of automobile from Acura

Abbreviation for Real Time Dampening
Symbol for Dedicated Sensor Ground Circuit

Abbreviation for Room Temperature Vulcanizing sealant.
  1. All the rubber seals, mats, and pads that cushion and protect vehicle windows, Trim, handles, bumper sections, carpets, etc.
  2. The tires.
  3. An elastic substance used in tires.
Rubber bush
A British term for Rubber bushing.
Rubber bushing
A tubular rubber sleeve for mounting a shaft or rod.
Rubber coupling
A flexible coupling using pressurized rubber blocks.
Rubber doughnut coupling
A typical flexible coupling, made of vulcanized rubber, shaped like a doughnut.
Rubber-isolated crossmember
A laterally aligned structural member that is attached to the body or the frame via vibration-absorbing rubber isolators. By bolting suspension or driveline components to such crossmembers, automotive engineers can reduce the transmission of noise and/or ride harshness to the body.
To coat or impregnate with rubber.
Rubber mallet
A hammer with a rubber head.
A system of rubber cushions and/or jointed engine mounts to isolate engine vibrations from the rider.
Rubber Neoprene
Rubber plug
A molded rubber stopper used to close cutouts or holes in body panels that have to be opened only infrequently, e.g., access holes for rustproofing of box sections.
Rubber ring
Rubber spring
An element of a rubber suspension system such as Hydrolastic suspension.
Rubber squeegee
A special spreader used for filling hollow, concave or rounded body areas; the rubber material adapts better to these surfaces than plastic spreaders and helps to prevent flat spots.
Rubber valve
Rubbing block
A little block located on the movable point that contacts the Distributor cam wheel and causes the points to open. A spring causes the points to close.
Rubbing compound
A polish that contains abrasives harsh enough to remove layers of dead paint. Useful in radical Restoration procedures, Rubbing compounds should not be used on new cars or those with delicate Finishes.
Rubbing strip
A strip of plastic at the widest point of the body, along doors and fenders down each side of the car to protect the bodywork from minor nicks, (as from the open door of a neighboring car).
Rudder stock
A vertical rudder shaft that connects to the steering gear.
Rudder stop
A stout bracket to limit the swing of the rudder to the maximum 37 degree starboard or port.
Rudge nut
A quick-release nut for central-locking wheels.
Rule of 78
A mathematical formula used in figuring a rebate of unearned charges or premium, when these charges were pre-computed and pre-paid. Once referred to as ’78 ways we get to keep your money’.
Rumble Seat
  1. A noise found in High-compression engines and associated with bending vibration of the crankshaft. It is caused by abnormally high rates of pressure rise near Top dead center.
  2. A vibration caused by loose Components.
Rumble seat
(RS) An open-air seat at the back of some older automobiles. Called a ‘dickey’ inBritain.
Rumble strip
  1. A series of small ridges placed across the driving lane to warn the driver that a stop sign is ahead.
  2. A series of grooves cut along the shoulder of the pavement. When a vehicle drifts over the rumble strips, a loud noise and vibration results, serving as a warning to sleepy or inattentive drivers.
  1. The trail of a paint drip; a dribble of paint
  2. To form a paint run which is usually caused by moving the spray gun too slowly or spraying too close to the panel surface thus causing an excessive build-up of paint.
  3. To start an engine and keep it going.

  1. An open sporting-type vehicle, lightweight, with two seats and with simple bodywork, i.e., a Roadster.
  2. A small car used strictly for driving in town
Runaway Lane
Runaway laneClick image to supersize

Emergency bypath next to a steep downgrade that a vehicle can steer into after losing braking power. Sometimes one to three lanes wide and several hundred feet long, the lane is a soft, gravel-filled pathway which helps to absorb the vehicle’s forward momentum, bringing it to a safe stop. Depending on the surrounding terrain, the ramp may be level or run up or down hill.

Runaway Truck Ramp
Emergency area adjacent to a steep downgrade that a heavy truck can steer into after losing braking power. Sometimes one to three lanes wide and several hundred feet long, the ramp is a soft, gravel-filled pathway which absorbs the truck’s forward momentum, bringing it to a safe stop. Depending on the surrounding terrain, the ramp may be level or run up or down hill.

Run channel
A U-section rubber used to hold glass parts and other body features in place or to protect panel edges.
Run flat
Damage sustained by a tire due to driving with insufficient air pressure or while flat. Some types of tires will allow you to run the tire with no air pressure for a short period of time.
Run-flat properties
The capability of a deflated tire to operate effectively, i.e., to permit further driving. To achieve this, the following must be fulfilled the tire beads must be retained against the rim flanges and on the rim bead seats when the tire deflates; the tire must be able to support all possible stresses imposed by deflation the tire must remain undamaged by internal friction and heat generated when running flat; the tire should be able to self-seal any punctures, so that the remaining air will be trapped and heat will be generated to reinflate the tire within limits.
Run-flat tire
A tire which can run for a certain length of time without air in it. In the inflated state, conventional tubeless tires perform the task of containing air and rolling. Once deflation occurs, the tire bead becomes dislodged from the rim bead seat and slides into the rim well. As a result of friction, the tire will become distorted and the rim may plough into the road, leading to loss of control and potentially resulting in an accident. Run-flat tires are designed to operate effectively with or without air, providing acceptable handling qualities when deflated, and good handling qualities when inflated.
Run in
A British term for Break-in.

A condition where a motor, engine, or feature is operating at least at its minimum requirement.

Running board
A long flat footboard on either side of a vehicle which acts as a step for passengers. They were particular common on vehicles before 1940.

Running fit
A fit in which sufficient Clearance has been provided to enable the parts to turn freely and to receive lubrication. Where sufficient clearance has been allowed between shaft and journal to allow free running without overheating.
Running gear
  1. The system of the engine, Transmission, drive shaft, differential, and wheels.
  2. The parts of the vehicle which cause the wheels to roll, i.e., suspension, steering components, springs, shock absorbers.
Driving a vehicle or running an engine or other mechanical unit at reduced speed and load when new, to prevent pick-up and seizure of the bearing surfaces, and to ensure even initial wear.
Running lights
A condition of a spark ignition engine in which fuel continues to burn after the ignition switch has been turned off, causing the engine to keep on running. Also called Dieseling.
Running-on control valve
Running on rails
Used to describe a car that is handling perfectly, as though it were actually attached to railroad tracks.
Running time
Amount of time a condensing unit Is run per hour or per 24 hours.
Running winding
Electrical winding of motor which has current flowing through it during normal operation of motor.
Run on
Condition when the engine continues to run, even when the key is turned off.


Run-on tire
A tire with a limited ability to run without air in it; sufficient to pull over safely. Compare Run-flat tire.
  1. The amount a gear or wheel moves in and out away from its true center as it is rotated. If runout is excessive the gear or wheel can be seen to wobble as it rotates.
  2. Side-to-side warpage of the brake disc friction surfaces. Measured with a dial indicator.
Runout point
To break, burst, or split.
Rupture member
A device that will automatically rupture at a predetermined pressure.
Rush-hour traffic
A road or area that is full of vehicles during peak time such as in the morning when commuters are going to work, at noon when people are going for lunch or coming back to work, and after work when people are going home.
  1. Oxidized iron or steel, the product of corrosion.
  2. To form rust.
Rust bucket
A colloquial term for a badly corroded car.
Rust converter
A chemical substance containing phosphoric acid etc. which transforms rust into a stable, firmly adhering iron compound by means of a chemical reaction.
Rust eater
A chemical or electrochemical destruction of iron and ferrous metals.
Rust inhibitor
A substance which reduces or prevents the formation of rust on iron and ferrous metals.
Rust inspection
A vehicle inspection conducted to detect rust and corrosion damage, usually by means of an Endoscope.
Rust killer
A substance which convert rust into a dry mass which can be removed with water.
Rust neutralizer
Rust pinhole
The early stage of rust penetration of a panel; rust pinholes will often reveal larger rust damage once the surface rust bubbles have been ground away.
  1. Resistant to rust.
  2. To make resistant to rust.
A process in which metal (such as iron and steel) is sealed from moisture and oxygen so that it will not corrode.

Rustproofing agent
An anti-corrosion, wax-based sealant.
Rust protection
Reducing the possibility of rust forming on iron and steel by coating with protective materials or by rendering them passive.
Rust remover
Any chemical substance which removes rust.
Rust sealer
A rust converter that provides a coat on metal surfaces to protect them against air exposure and thus to prevent continued corrosion.
A depression in a roads made by continuous passage of heavy vehicles.
A vehicle brand of which the 1925-1948 models are classic cars.
Abbreviation for Recreational vehicle. There are seven forms of recreational vehicles

Abbreviation for Reid Vapor Pressure
Rollover/vapor separator valve.
Rear Wheel Anti-Lock (Chrysler and General Motors).
Abbreviation for Rear-wheel drive.
Abbreviation for Road Weather Information Systems
Abbreviation for raised white letter, as in rwl tires.


Abbreviation for receive data line

Rzeppa-type joint
A constant velocity joint incorporating balls as a means of torque transmission. Named after Alfred Rzeppa, a Ford engineer.
Rzeppa-type universal joint
A constant velocity joint incorporating balls as a means of torque transmission. Named after Alfred Rzeppa, a Ford engineer.