Automotive Glossary
Automotive Glossary
Browse the glossary using this index
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RacistIntolerance of race. A person with prejudiced belief that one race is superior (better) than another. | |
RackGear teeth cut on a straight bar or rod. | |
Rack and PinionType of steering system gearing. | |
RadialOutwards from the centre and at right angles to the axis. | |
Radial (Tire)Tread supported by crown plies and casing plies laid radially. | |
Radial (Tyre)Tread supported by crown plies and casing plies laid radially. | |
Radial ForceA force that acts outwards from a centre point. | |
Radial GrooveA groove running radially, or radiating from the centre and around a component. | |
Radial PlayFree play at right angles to the axis. | |
Radial RunoutOut of true movement at the periphery of a rotating circular component. | |
Radial-pistonUsually refers to a pump where a number of pistons are used that act outwards from the centre. | |
RadiationThe emission and diffusion of rays. | |
RadiatorAn apparatus for radiating or diffusing heat. | |
Radiator CapCap used to pressurise cooling system. | |
RadiusThe straight line distance from the centre of a circle to any fixed point on the circumference. | |
Radius ArmSuspension link with a fixed inner bearing and support for the stub axle assembly at the outer end. | |
Rail(1) Gear selector component carrying the selector forks in a manual transmission. (2) Pressurised petrol supply tube for all fuel injectors in a port electronic fuel injection system. | |
RAMRandom Access Memory. Dynamic memory in computers which holds data being worked on. This data is not permanent and will be lost when power is switched off. | |
Ram Air EffectForced movement of air due to the movement of the vehicle. | |
Ram CylinderHydraulic cylinder that applies force to a rod. Often part of a steering system. | |
Ram PressurePressure caused by air of fluid movement. | |
RangeThe difference between the highest and lowest numbers. | |
Rare earth magnetsThese magnets are made from substances which hold a more dense magnetic flux than regular magnets. This means more power for the weight. Rare earth magnets are always preferable although not necessary as they can be expensive. | |
RatchetA mechanism consisting of a toothed wheel, the ratchet, and a locking or actuating pawl. Used to either prevent the pawl lever or the wheel from rotating in one direct only or in some mechanisms to drive the wheel forward. | |
RatioThe numerical relationship between two or more components transmitting a force or movement. | |
Ravigneaux Planetary GearsAn epicyclic gear set with two sun wheels and planetary gears on a common annulus. | |
Re-faceTerm used to describe the action when the face of a valve or other component is machined. | |
ReactTo respond. | |
ReactionAn equal and opposite force. | |
Reaction MemberThe held component of an epicyclic gear train that produces the specific gear ratio when held. | |
ReactorPart of a fluid flywheel that reacts to the movement of fluid. | |
Ready-To-SprayDescribes paint which has been properly mixed with all necessary components and is ready to apply to the substrate. A variation is 'Ready-for-Use' (RFU) which refers to material that is purchased ready to apply straight from the container. | |
ReamedAccurate cutting of a hole using a reamer. | |
ReboreRecutting of a cylinder bore to an oversize dimension to remove wear and or damage. The cylinder is then fitted with oversize pistons. | |
ReboundSuspension movement following compression of the spring when the energy of impact is released. | |
ReceiverDevice used to receive or pick up radio signals or similar. | |
Receiver/DrierPart of an air conditioning system in the high pressure side between the condenser and expansion valve that acts as a reservoir and as a filter and drier for the refrigerant. | |
RecessAn undercut area in a component usually machined to give access for a fixing or another component. | |
RechargingPutting back the electricity taken from a battery. | |
ReciprocalThe value of something when divided into one. The reciprocal of R is 1/R. | |
ReciprocatingMoving backwards and forwards. | |
Recirculating Ball SteeringA steering gearbox using the nut and worm principle. It has a series of ball bearings forming the thread of the worm, which gives a very smooth operation. | |
RecoatingThe application of fresh paint material over a recently painted material. | |
Recombinant BatteryA type of battery design which has slightly more negative plate material than positive plate material allowing the oxygen released by the positive plates, near to the fully charged position, to combine with the negative plate so that no gases are discharged. | |
RectifierAn electrical device that converts alternating current AC to direct current DC. | |
ReduceTo lower the viscosity of a paint by the addition of solvent or thinner. | |
ReducerA solvent used to reduce or thin paints to sprayable viscosity. | |
Reduction GearA gear (or more often pair of gears) used to reduce the speed of a shaft. | |
RedundantIn the context of systems or message transmission, redundant means extra information on say another channel that may not be used except for checking. | |
Reed RelayThin steel contacts that are joined when they become magnetic. The magnetism is created by a small coil, usually in series with a bulb. | |
Reed SwitchThin steel contacts that are joined when they become magnetic. | |
Reference VoltageA voltage value used in an electronic control module that is conducted to a sensor and against which the return voltage is measured in order to determine the signal value. | |
RefinishRepair of an OEM or previously painted substrate. | |
ReflectorBody or surface reflecting rays, particles, objects. Legal requirement on rear of vehicles. | |
RefractionDeflection at a certain angle when light enters obliquely from another medium of different density (light lens). | |
RefrigerantThe gas in an air conditioning system. It is condensed to a liquid by pressurisation and the heat in the refrigerant is taken in or passed out during the changes of state from liquid to gas and from gas to liquid. Two refrigerants are used for vehicle air conditioning. These are R12 and R134a. These must not be mixed or allowed to escape to the atmosphere. | |
Regenerative brakingA regenerative brake is an energy recovery mechanism that reduces vehicle speed by converting some of its kinetic energy and/or potential energy (due to elevation) into a useful form of energy instead of dissipating it as heat as in a conventional brake. | |
RegulatorAn electronic device for controlling the output voltage from a generator. | |
Regulator TerminalsTerminals on the regulator that connect to, for example, a warning light, field windings, sensing supply and ignition. Some also output signals to the engine management ECU. | |
ReinforceTo make information sink in. | |
Relative DensityThe ratio of the density of one substance to the density of water. Used to measure battery acid strength. Specific gravity is a similar but older term. | |
RelayElectromagnetic switch used in electric circuits to reduce load on smaller switches. | |
Relay CoilThe winding in a relay that when power is supplied to it, causes magnetism, which in turn makes the relay contacts close. | |
RelaysElectromagnetic switches used in electric circuits. | |
Release BearingShaft-mounted thrust bearing that transmits the action of the clutch pedal to disengage the clutch. | |
Release FingersThe fingers in a circular section of the diaphragm on a clutch that move when the release bearing is operated. | |
Release ForkThe actuating lever that moves the release bearing of a clutch. | |
Release LeversSee Release Fork. | |
Release MechanismComponents joining the clutch pedal to the pressure plate of the transmission clutch. | |
Release ShaftPivot for the clutch release lever. | |
Relevant InformationThe suitability of information based upon your needs. | |
Relief ValveSee Pressure Relief Valve. | |
ReluctanceA measure of resistance to magnetic forces. | |
REMCORemote adjustment for CO. | |
Remote StarterA switch, usually connected directly to the solenoid terminal of the starter motor, to allow remote operation during repair or testing. | |
Renewable resourceA natural resource is a renewable resource if it is replaced by natural processes at a rate comparable or faster than its rate of consumption by humans. Solar radiation, tides, winds and hydroelectricity are perpetual resources that are in no danger of a lack of long-term availability. | |
Replacement manual pagesReplacement pages are normally sent out under a Special Notice. They must be inserted into the manual immediately. Superseded pages should be removed. | |
ResearchTo study something thoroughly. | |
Reserve CapacityThe time for which a battery will produce 25A at 25C. | |
ReservoirA container holding a supply of liquid, gas, air or vacuum in a system. | |
Residual MagnetismThe magnetism held in an electromagnetic pole after the electrical current has been turned off. Natural magnetism in a magnet. | |
Residual PressureThe pressure held in a hydraulic line after a valve has closed and is used to reduce the pressure build up time when next applied. | |
ResilienceA property of material that has the ability to absorb energy from sudden loading by extension and resistance to fracture from stress loadings. | |
ResinA solid or semisolid material, usually polymeric, which deposits a film and is the actual film-forming ingredient in paint. Solutions of polymers are often called resins, but the term actually applies only to the film forming solids, not to the solution. | |
Resistance(1) Electrical resistance, the Ohm, is a measure of the opposition to electrical current flow in a conductor. (2) A force that acts in opposition to another. | |
Resistance TestA measurement of resistance using an ohmmeter. | |
ResistorElectrical device which has resistance to the passage of current. | |
Resistor PackSet of dropping resistors used as part of a heater motor circuit to set different speeds. | |
ResolutionThe number of pixels per square inch shown on the computer screen. The greater the resolution the better the picture. | |
Resonant FrequencyVibration at the natural frequency of a component. | |
Resonant NoiseA noise that results from vibration at the natural frequency of a component. | |
ResonatorComponent of the exhaust system to reduce noise. | |
ResourcesSources of information, expertise and knowledge. | |
RespiratorA device worn over the face to filter particles and fumes out of the air being breathed. Modern 2K paints require the use of air-fed respirators which provide an efficiently filtered supply of air at a positive pressure around a half-or full-face mask worn by the painter. | |
RestrictorA narrowing of a passage used to control flow of a gas or liquid. | |
Resultant ForceA force acting in one direction as result of other forces acting on an object from other directions. | |
RetarderA slow-evaporating solvent added to a paint to prolong the drying time. Typically used to reduce orange peel or blushing. | |
RetrofitThe fitting of a system after the vehicle has left the factory or later in its life. | |
RetrofittedRetrofitting refers to the act of adding new technology or features to older systems. | |
ReturnPipe or similar where, for example, fuel is returned to the tank. | |
Return SpringSimple spring to move an item back into its rest position. | |
RevcounterA tachometer that indicated revolutions per second. | |
Reverse BiasAn electrical term applied to semiconductors and transistors which normally allow the flow of current in one direction only but will allow current to flow in the opposite direction under specific conditions. | |
Reverse SwitchA switch operated by a gearbox component that illuminates the reverse light. | |
Reversing CircuitA circuit using changeover switches or relays that reverses the voltage supply to a motor. | |
ReviewTo look over and study information again. | |
RevisionTo review information in order to remind yourself of its content. | |
RFIRadio frequency interference. Electromagnetic radiation from an electrical source. | |
RfRReason for Rejection | |
RHDRight-Hand Drive | |
RheostatA type of variable resistor having only two terminals. | |
Rich Fuel/Air MixtureA fuel/air mixture with a ratio greater than the stoichiometric ratio of 14.7:1. A mixture strength with an excess of fuel. | |
RimOutside edge, periphery. Part of wheel carrying the tyre. | |
Ring Gear (Starter)A large diameter gear wheel mounted on the engine flywheel or torque converter flex plate and used to engage with the starter motor drive pinion to start the engine. | |
Ring GrooveSlot cut round the piston for the piston rings to sit in. | |
Ring LandSeating area for piston rings. | |
RIRORubbish In Rubbish Out. In relation to the Internet. | |
Road AdhesionGrip between the tyres and the road surface. | |
RockerA component such as a lever to operate a valve due to action of a cam. | |
Rocker ArmArm that works on a rocker shaft to open a valve on an overhead valve engine. | |
Rocker ShaftA shaft, usually at the top of an overhead valve engine, on which the rockers pivot. | |
Rocker SwitchA switch that has two or three positions. Often used with the centre as an off position and then with a voltage reversal process as it is rocked in either direction. | |
RollVehicle body movement from side to side. | |
Roller BearingA type of bearing consisting of a series of parallel rollers held in a cage between inner and outer bearing tracks. | |
Roller PumpA type of fuel pump that uses a rotor and a series of parallel rollers in an elliptical casing to produce the pumping and carrying chambers of the pump. Usually electrically driven and used on many fuel injection systems. | |
Roller-Cell PumpA type of fuel pump that uses a rotor and a series of parallel rollers in an elliptical casing to produce the pumping and carrying chambers of the pump. Usually electrically driven and used on many fuel injection systems. | |
Rolling ResistanceThe frictional value for the circumferential surface of a rolling component in contact with the track or road on which it runs. An example is the rolling resistance of a road tyre on various road surfaces. | |
Rolling RoadRollers set into the ground on which the wheels of a vehicle can be run. The system can then be used to check performance under driving conditions. | |
ROMRead Only Memory in a computer, which is the permanent memory that is retained even when the power is switched off. | |
RONRated Octane Number | |
RoofAdditional structural panel of vehicle body. | |
Roots SuperchargerType of mechanical pressure charger using two twin or triple lobed rollers to form an air pump in the inlet tract of an engine. | |
Rotary Air ValveA valve that uses a shutter to cover a hole depending on the amount of rotation. Usually used to refer to an auxiliary air valve on an injection system. | |
Rotary Control ValvePower steering control valve coupled to the steering column, which operates by inner and outer components coming together to open valve orifices to allow hydraulic fluid flow. | |
Rotary MovementCircular motion. Movement provided by the basic gear wheel or crank. | |
Rotary Oil PumpA positive displacement oil pump that uses two rotors inside a housing. There is an eccentrically driven rotor with eternal lobes that mesh with the internal lobes of a driven rotor. The external rotor has one more lobe than the internal rotor and this forms the pumping and carrying chambers of the pump. | |
Rotary PumpType of diesel fuel injection pump. | |
Rotoflex JointA propeller shaft universal joint using a sleeved hexagonal rubber ring between alternate three pointed couplings on each of the two connecting shafts. | |
RotorA component that rotates! Such as a brake disc, alternator rotor or oil pump rotor. | |
Rotor WindingsCopper windings that create the magnetic field on the alternator rotor. | |
Rounding OffExpress as a round number (i.e., 4.7 rounded off becomes 5) | |
RPMRevolutions per minute. | |
RSIRepetitive Strain Injury. This type of injury occurs from repeated physical movements. It can be caused by bad typing technique, bad posture and lack of adequate rest and breaks. RSI is common in the wrists. | |
RTVRoom temperature vulcanizing. A type of form-in-place gasket material. | |
Rub-throughThe result of sanding or buffing through one layer of paint and into the substrate below. A rub-through is common from clearcoat to basecoat or from primer to metal. | |
Rubber MountingsHard rubber connection units used to insulate one component from another to reduce vibrations and noise. | |
Rubbing CompoundAn abrasive that smoothes and polishes the paint film. Also known as polishing compound. | |
Run-outA measure of the out-of-true state on the face or faces of rotating components such as brake rotors and the clutch face on engine flywheels. | |
RunnerAn engine intake tube joining the plenum chamber to the inlet port in the cylinder head. | |
Running ClearanceA small gap between moving components that allows movement and lubrication. | |
Running OnThe term applied to an engine that continues to run after the ignition has been switched off. Also run on and dieseling. | |
RunoutA measure of the out-of-true state on the face or faces of rotating components such as brake rotors and the clutch face on engine flywheels. | |
RustThe corrosion product that forms on a steel surface when it is exposed to oxygen and water. Also known as oxidation. | |
RWDRear Wheel Drive. | |
Rzeppa JointA type of constant velocity joint used on vehicle transmission drive shafts. It has 6 steel balls in a cage between inner and outer elliptical housings. | |