AutoZone Glossary | r

Search suggestions

    My Vehicles

    1998 Mazda Truck B3000 2WD 3.0L MFI 6cyl

    Find a Store

    Select Store

    GET A $25 GIFT CARD FOR EVERY $100 SPENT ON ONLINE SHIP TO HOME ORDERS.

    Use Code: SALE25

    See Details

    GLOSSARY TERMS

    R

    R&D
    An abbreviation for research and development.
    R&R
    An abbreviation for remove and replace.
    R-12
    A trade term for refrigerant CFC-12.
    R-134a
    A trade term for refrigerant HFC-134a.
    R-22
    A trade term for refrigerant HCFC-22.
    Racer's tape
    Duct tape.
    Races
    The metal rings on which ball or roller bearings rotate.
    Rack and Pinion
    A type of steering assembly that has a gear or pinion at one end of the steering shaft engaging a horizontal-toothed bar or rack having tie rods at either end that are attached to the steering arms.
    Rack-and-Pinion Steering
    A term used for rack and pinion.
    Racy Bopper
    An auto-racing groupie.
    Rad
    A term often used to describe a radically modified engine or vehicle.
    Radial Compressor
    A space-saving compressor used on small cars.
    Radial Motion
    A motion extended to either, or both, extremes of a radius.
    Radial Ply
    A term used for radial ply belted tire.
    Radial Ply Belted Tire
    A tire having the ply cords placed at right angles to the beads, plus belts under the tread section providing the least tread distortion while moving, thereby minimizing tread wear and rolling friction.
    Radial Runout
    Variations in tire diameter; the measured amount of out-of-roundness on rotating tires.
    Radial Tire Waddle
    A term used for tire waddle.
    Radiation
    A natural process by which energy is transmitted.
    Radiation Dose
    The amount of energy per unit of mass of material deposited at each point of an object undergoing radiation.
    Radiator
    A heat exchanger used to remove heat from the coolant in the cooling system containing a vertical- or horizontal-finned tubing section connected between two tanks.
    Radiator Cap
    A term used for radiator pressure cap.
    Radiator Core
    The center of the radiator, made of tubes and fins, used to transfer heat from the coolant to the air.
    Radiator Fan
    A term used for fan.
    Radiator Hose
    An oil- and ozone-resistant synthetic-rubber hose that connects the radiator to the thermostat outlet housing and water pump inlet housing.
    Radiator Hose Clamp
    A term used for hose clamp.
    Radiator Pressure Cap
    A cap that seals in pressure from hot expanding coolant until a predetermined limit is reached, then the valve opens, allowing excess pressure to escape, generally to a coolant-recovery tank.
    Radiator Shutter System
    An engine temperature-control system that controls the amount of air flowing through the radiator by use of a shutter system.
    Radius
    A line extending from the center of a circle to its boundary.
    Radius Arms
    Longitudinal suspension arms used to position a beam axle.
    Radius Ride
    A condition where the crankshaft rides on the edge of the bearing.
    Radius Rods
    A term used for radius arms.
    Radiused
    A procedure that is used to reduce the radius diameter at the area the valve stem meets the valve head.
    A valve type that is ground with a radial grinder to aid in air flow around the valve.
    Wheelwells that have been cut to a circular shape.
    Radix
    A base.
    The base number in a number system.
    Rag Top
    A convertible.
    Ragged Edge
    The absolute limit of a vehicle's potential.
    Rail
    An early dragster with exposed frame rails.
    Rail Job
    A term used for rail.
    Rake
    A suspension or structural design to lower one end of the vehicle in relation to the other end.
    Rally
    A sports-car driving contest for driver performance as opposed to vehicle performance.
    RAM
    An acronym for random access memory.
    Ram Air
    Air forced through the radiator and condenser coils by the movement of the vehicle or the action of the fan.
    Ram Air Cleaner
    An air cleaner for high-performance cars that opens an air scoop on the hood to provide a ram effect when the throttle is wide open.
    Ram Induction
    An intake manifold designed to cause a resonant effect at a specific predetermined engine speed.
    Ram Tubes
    Short, tuned, tubular stacks on the top of carburetors.
    Ram Tuning
    The tuning of an intake manifold to ensure that the passages are of sufficient length to cause a resonant effect at a specific predetermined engine speed.
    Ramp
    The sloping section of a camshaft lobe which raises the lifter.
    Ramp Angle
    An angle formed by lines adjacent to the static-loaded radius of the front and rear wheels intersecting at the point of the lowest ground clearance under the middle of the vehicle.
    Ranco Control
    A tradename often used for a thermostat.
    Random Access Memory (RAM)
    A computer memory into which the user can enter information and instructions (write), and from which the user can call up data (read).
    Random Intermittent Welds
    Welds on one or both sides of a joint in which the weld increments are made without regard to spacing.
    Range Shift Cylinder
    Located in the auxiliary section of the transmission, this component, when directed by air pressure via low and high ports, shifts between high and low range of gears.
    Range Shift Lever
    Located on the shift knob, this lever allows the driver to select low- or high-gear range.
    Raster Pattern
    Also known as stacked pattern.
    Rat
    A Chevrolet big block V-8 engine.
    Rat Motor
    A Chevrolet big block V–8.
    Ratio
    The relative amounts of two or more substances in a mixture.
    The comparison of two numbers as in teeth on gears.
    Ratio Valve
    A device used on the front or steering axle of a heavy-duty vehicle to limit the brake application pressure to the actuators during normal service braking.
    Ravigneaux Gear Train
    A planetary gear train with two sun gears, three long and three short planetary pinions, planetary carrier, and ring gear.
    RC Engine
    A shortened term for rotary combustion engine.
    RCRA
    An abbreviation for Resource Conservation and Recovery Act.
    Reaction Time
    The amount of time required to physically apply the brakes of a vehicle after mentally being aware of the necessity to do so.
    The amount of time required from the moment the Christmas tree light turns green until the vehicle trips the starting-line timing light.
    Reactivity
    The characteristics of a material that cause it to react violently with another material, such as air, heat, or water.
    Read-Only Memory
    A solid-state storage chip that is programmed at the time of its manufacture, cannot be reprogrammed by the computer user, and retains its program when the computer's power is turned off.
    Rear Clip
    The rear end of a vehicle's bodywork extending from the door pillar back.
    Rear Control Arm
    Horizontal arms that connect the rear axle housing to the frame when coil springs are used in the rear suspension system to maintain axle alignment and handle the driving and torque loads.
    Rear Drive
    A term used for rear-wheel drive.
    Rear End
    The differential and final drive assembly on a rear-wheel drive vehicle.
    Rear Engine
    An engine arrangement where the engine is placed behind the rear wheels, driving them through a transaxle assembly.
    Rear Leaf Spring
    A term used for leaf spring.
    Rear Roll Center
    The center as determined by the rear suspension geometry around which the rearward part of a vehicle has a tendency to roll.
    Rear Shock
    A type of shock absorber that is compatible with a particular type of driving and its load requirements.
    Rear Steer
    A steering gear that is positioned behind the front-wheel centerline.
    Rear Suspension
    An integral part of the total suspension system designed to keep the rear axle and wheels in their proper position under the car body, typically of two types; solid-axle type and independent rear-suspension type.
    Rear-Axle Assembly
    A group of parts that operate to transfer driving torque from the drive shaft to the rear wheels, and includes mounting pads for the rear springs and shocks.
    Rear-Axle Housing
    The basic framework of the rear-axle assembly inside which the individual parts, including the differential and axles are mounted and/or operate.
    Rear-Camshaft Plug
    A plug driven in the rear of the block behind the camshaft to contain the oil supplied to the rear camshaft bearing.
    Rear-End Torque
    The twisting reaction of a rear-axle assembly in a direction opposite to that of wheel rotation when power is applied, controlled by the control arms in coil-spring models and by the leaf springs in leaf spring models.
    Rear-Spring Shackle
    A device bolted to a rubber bushing in the rear main leaf eye, and having an upper shackle bolt that extends through a similar rubber bushing in the rear-spring hanger, providing fore and aft movement with variations in spring length.
    Rear-Suspension Coil Spring
    A coil spring that is used in the rear suspension system.
    Rear-Suspension Rebound Stop
    A function of the rear shocks as they limit the distance the rear-axle assembly can move downward.
    Rear-Wheel Drive
    A drivetrain layout that provides power to the rear wheels only. Often referred to an rear drive.
    Reassembly
    Putting the disassembled parts of a device back together, replacing those parts as necessary.
    Rebore
    To increase the diameter of a cylinder.
    Rebound
    The outward extension of the springs and shocks in a vehicle suspension system.
    Rebound Clip
    Metal clamps placed at three or four intervals around multi-leaved springs to prevent the leaves from becoming separated on rebound.
    Rebound Travel
    The downward movement of a wheel from its normal position when the spring and shock are expanding, as the sudden drop of a wheel into a depression and a weight transfer away from the wheel.
    Rebound Valve
    A calibrated piston valve mounted on the shock piston that provides variable resistance to fluid flow during rebound.
    Recall
    A notice issued by the vehicle manufacturer that a certain make and model vehicle should be returned to the dealer for a correction of a suspected or known problem.
    Recall Bulletins
    A dealer notice pertaining to vehicle service or the replacement of parts related to a recall.
    Recapping
    To recover a tire casing with a new tread.
    Receiver
    A term sometimes used for drier, receiver drier, or receiver dehydrator.
    A container for the temporary storage of liquid refrigerant.
    Receiver Dehydrator
    A combination container for the storage of liquid refrigerant and a desiccant.
    Receiver Drier
    A term used for receiver dehydrator.
    Receiver Tank
    The second tank in a radiator is often referred to as a receiver because it receives coolant after passing through the many tubes of the radiator core. The receiver, on automatic transmission equipped cars, contains a transmission oil cooler.
    Receptacle
    A contact device, installed at an electrical outlet, extension cord, or drop light for the connection of an attachment plug and flexible cord to supply power to portable equipment.
    Recharging
    The action of forcing electrical current into a battery, reversing the chemical reaction between the plates and electrolyte.
    Filling an air-conditioning system with refrigerant after repairs are made.
    Reciprocating
    A back-and-forth, up-and-down, or to-and-fro motion, such as that of a piston in a cylinder.
    Reciprocating Engine
    A powerplant in which the pistons move in a reciprocating motion.
    Reciprocating Motion
    The motion of an object between two limited positions in a straight line back and forth or up and down.
    Recirc Door
    An abbreviated form of recirculate door.
    Recirculate Door
    A door in the plenum that regulates the amount of recirculated air flow.
    Recirculating Ball
    A worm and gear steering assembly with balls between the worm and sector to reduce friction.
    Recirculating-Ball Steering Gear
    A low-friction steering gear box having a worm-gear meshing with a cross shaft sector through about 40 recirculating balls that travel in matching grooves inside the ball nut and outside the worm shaft which acts as a rolling thread.
    Recirculating-Ball-and-Nut Steering Gear
    A type of steering gear having a nut meshing with a worm gear sector, with balls that circulate between the nut and worm threads.
    Reclaim
    To process used refrigerant to new product specifications by means that may include distillation. This process requires that a chemical analysis of the refrigerant be performed to determine that appropriate product specifications are met.
    Recombination Battery
    Sometimes called dry-cell batteries because they do not use a liquid electrolyte solution.
    Recon
    A short term for reconditioned.
    Reconditioned
    A used part that has been repaired, tested, and determined to be in good order. Also known as recon.
    Recovery
    The recovery of refrigerant is to remove it, in any condition, from a system and to store it in an external container without necessarily testing or processing it in any way.
    Recovery Cylinder
    A cylinder for the storage of used R-12 and/or R-134a must meet DOT specification 4BA-300, characterized by a combined liquid/vapor valve located at the top. A recovery cylinder should be painted grey with a yellow shoulder.
    Recovery/Recycle Systems
    A term often used to refer to the circuit inside the recovery unit used to recycle and/or transfer refrigerant from the air-conditioning system to the recovery cylinder.
    Recovery/Recycle Unit
    A term used to identify the complete unit used to recover and/or recycle refrigerant from the air-conditioning system.
    Recreational Vehicle (RV)
    A motor-driven, van-like vehicle having sleeping, food preparation, and bathroom facilities.
    Rectifier
    An electrical device used to convert alternating current to direct current.
    Rector
    The stator in a torque converter.
    Recycle
    To recycle is to clean the refrigerant for reuse, by oil separation and passes through other devices such as filter-driers, to reduce moisture, acidity, and particulate matter.
    Red Book
    A used-car price guide.
    Red Dye Trace Solution
    The dye that reveals the exact location of a leak in a fluid system by depositing a colored film around the leak area.
    Red Flag
    A signal for all drivers to come to a stop.
    Red Light
    In normal driving situations, a warning to stop.
    In drag racing, to jump from the line before the start signal.
    In competition, to foul and become disqualified for an event.
    Red Line
    The absolute minimum an auto dealer will accept for a vehicle.
    The absolute maximum recommended engine speed.
    Reducer
    A tool that reduces the size of a device, such as a pipe.
    A paint thinner.
    An adapter for using a smaller tool.
    Reducing Atmosphere
    A chemically active protective atmosphere, which at elevated temperature will reduce metal oxides to their metallic state.
    Reducing Flame
    An oxyfuel gas flame with an excess of fuel gas.
    Reduction Catalyst
    The section of a three-way catalytic converter that breaks NOX (oxides of nitrogen) down into harmless nitrogen and oxygen through a reduction reaction.
    Reed Valve
    A thin leaf of steel located in the valve plate of automotive compressors, serving as suction and discharge valves.
    Reference Voltage
    In computerized engine-management systems, a five-volt signal sent out from the electronic control unit to a variable-resistance sensor such as a throttle-position sensor so the computer can read the voltage value of the return signal.
    Refrigerant
    The chemical compound used in a refrigeration system to produce the desired cooling effect.
    Refrigerant CFC-12 (R-12)
    The refrigerant, dichlorodifluoromethane (CCl2F2), used in automotive air conditioners, as well as other air-conditioning and refrigeration systems.
    Refrigerant HCFC-22 (R-22)
    A refrigerant, monochlorodifluoromethane (CHC1F2), used in some early automotive applications but not to be used for today's automotive air conditioners because of high pressures.
    Refrigerant HFC-134a (R-134a)
    The refrigerant of choice, tetrafluoroethane (CH2FCF3), to be used in automotive air conditioners as R-12 is being phased out.
    Refrigerant Lines
    Specially designed vapor-barrier hoses reinforced with woven nylon mesh and fabric capable of withstanding the high temperatures and pressures of the system.
    Refrigerant Recovery
    The act of recovering refrigerant.
    Refrigerant Recycle
    The act of recycling refrigerant.
    Refrigerant-Containment Device
    A device introduced on some car lines to guard against high pressure resulting in refrigerant loss by controlling the compressor and/or condenser fan motor.
    Refrigeration
    To use an apparatus to cool; keep cool; or keep chilled under controlled conditions by natural or mechanical means, as an aid to ensure personal safety and comfort.
    Refrigeration Cycle
    The complete cycle of the refrigerant back to the starting point, evidenced by temperature and pressure changes.
    Refrigeration Lubricant
    A mineral oil or synthetic oil-like lubricant, such as PAG and ESTER, that is formulated for specific use and application in designated refrigeration systems.
    Refrigeration Oil
    A highly refined (specially formulated), non-foaming organic mineral oil free from all contaminants, such as sulfur, moisture, and tars, used to lubricate the air-conditioner compressor.
    Refrigeration Tape
    A term used for insulation tape or duct tape.
    Regeneration System
    A system in a gas turbine that converts some of the heat, usually wasted, into usable power.
    Regenerator
    A device placed on a gas turbine to take the heat of exhaust and put it into the intake of the engine.
    Regional Offices and Distributorships
    Offices owned and operated by the automobile company, and considered to be the link between the manufacturer and the dealerships.
    Register
    A high-speed device used in a central processing unit for temporary storage of small amounts of data or intermittent results during processing.
    Regular Gasoline
    Gasoline that has an octane number near 85–90.
    Regular Production Option (RPO)
    Items of new car equipment available to any buyer for a price.
    Regular-Duty Coil Spring
    A coil spring supplied to handle average loads to which the vehicle is subjected, having a small wire diameter as compared to a heavy-duty spring.
    Regulator
    A term often used for voltage regulator.
    Reheat Principle
    A principle that is used in automotive air-conditioning systems to control in-car relative humidity by first cooling, then reheating the air.
    Reid Vapor Pressure (RVP)
    The measure of the volatility of liquid fuels.
    Relative Humidity
    The moisture content of the surrounding air.
    Relative Pressure
    The difference between intake manifold pressure and the output pressure in a fuel-injection system.
    Relative Wheel Weights
    The weight on each of the vehicle's wheels as measured by individual matched scales under each wheel.
    Relay
    An electro-mechanical switch having a coil and one or more sets of points.
    Relay Rod
    A term used for center link.
    Relay/Quick-Release Valve
    A valve, similar to a remote control foot valve, used on trucks with a wheel base of 254 inches (6.45 meters) or longer attached to an air tank to main supply line to speed the application and release of air to the service chambers.
    Release Bearing
    A term used for throwout bearing.
    Release Fingers
    A term used for release levers.
    Release Levers
    A lever-type, pivoting pressure-plate device in the clutch assembly that is moved by throwout bearing movement, causing the clutch-spring pressure to be relieved so the clutch is released from the flywheel.
    Reliability Run
    A rally for hot rod drivers.
    Relief Valve
    A term used for compression valve or pressure relief valve.
    Relieved
    An engine in which the intake and exhaust passages have been cleaned of all obstructions and ridges.
    Reluctor
    A gear-like part of an electronic ignition system, having the same number of teeth as there are cylinders, near the top of the distributor shaft so that as a tooth passes a pickup coil, resistance to magnetic flux is reduced and the magnetic field is strengthened, which triggers the electronic control unit.
    Remote Back-Pressure Transducer
    An exhaust back-pressure sensing device mounted in the vacuum line leading to the EGR valve rather than on the valve itself, to bleed off the vacuum signal to prevent recirculation.
    Remote Bulb
    A sensing device connected to an expansion valve or thermostat by a capillary tube, sensing temperature and transmitting pressure to the control for its proper operation.
    Remote Sensing Bulb
    A term used for remote bulb.
    Remove and Repair
    To remove a component from a vehicle and then to repair it; it is assumed that it will also be replaced on the vehicle.
    Remove and Replace (R&R)
    To remove a component and replace it with a reconditioned, rebuilt, good used, or new component on a vehicle.
    Repair Order
    A written summary report of repairs that are requested or that are made.
    Replacement Springs
    New springs having the same characteristics, shape, and type of ends as the springs in the vehicle, all four of which should be replaced at the same time.
    Replacement Tire
    A tire purchased to replace an original tire that was supplied by the vehicle manufacturer, having the same size and temperature range as the original tire.
    Required Sidewall Information
    Information that is required by the Department of Transportation to be included on each tire such as size, load rating, maximum inflation pressure, generic name of materials used in construction, actual number of plys, and so on.
    Required Voltage
    The low voltage required by a device or system.
    The highest voltage required to fire a spark plug.
    Research and Development (R&D)
    As the term implies, to research and develop a concept, system, or product.
    Research Octane Number (RON)
    A term used for octane number.
    Reserve Capacity
    A term used for reserve capacity rating.
    Reserve Capacity Rating
    The number of minutes a fully charged battery at 80°F (26.7°C) can supply power at 25 amperes to run the ignition, lights, and accessories after a charging system failure or when the engine is not running, before dropping to 1.75 volts per cell.
    Residual Magnetism
    The magnetism that remains in an electromagnet material after the current is interrupted.
    Residual Pressure
    The pressure that is retained in a specific area.
    Residual Stress
    Stress present in a joint member or material that is free of external forces or thermal gradients.
    Resin
    The molten plastic part of fiberglass-reinforced plastic.
    Resistance
    An opposition to the flow of electricity.
    An opposition to movement, such as wind against a vehicle.
    Resistance Welding
    A term used for spot welding.
    A welding process that unites the surfaces with heat, obtained from the resistance of the work pieces, and the application of pressure.
    Resistor
    An electrical device used to reduce voltage.
    Resistor Spark Plug
    A spark plug having a resistance of 5,000 to 10,000 ohms inside the upper part of the insulator, increasing the electrode life and suppressing radio interference.
    Resonator
    A small auxiliary muffler, after the main muffler, used to help reduce engine noise without restricting the flow of exhaust gas.
    Resource Conservation and Recovery Act (RCRA)
    A Federal law that requires users of hazardous materials to store used material in a manner consistent with established guidelines until they can be properly disposed.
    Resto
    The restoration of an old car.
    Restriction
    A blockage in an air or fluid line caused by a pinched or crimped line, foreign matter, or moisture freeze-up.
    Restrictor
    An insert fitting or device used to control the flow of air or fluid.
    Restrictor Plate
    A plate with holes drilled in it to restrict the flow of air or liquid.
    A plate with holes of a calibrated diameter that is placed between the carburetor and intake manifold of a stock car to restrict the air/fuel flow, thereby reducing engine speed and horsepower.
    Restyle
    To customize a vehicle.
    To change the appearance of a vehicle.
    Retard
    To cause ignition spark to occur later in an engine's cycle.
    Retard Sensor
    A term used for knock sensor.
    Retarder
    A mechanical, electrical, or hydraulic device used to slow a diesel engine when the throttle is lifted.
    A chemical compound that reduces the speed of paint drying.
    Retention Seal
    A seal that has the ability to retain fluid pressure.
    Retracting Spring
    A spring that is used to pull the brake shoes away from the drum when the brake pedal is released, pushing the wheel-cylinder piston back into its bore and thus returns the brake fluid to the master cylinder.
    Retread
    A used tire having had its old tread removed and a new tread applied.
    Retrocar
    A modern vehicle that has been restyled to look like an old vehicle.
    Retrofit
    To modify equipment that is already in service using parts and/or materials available or made available after the time of original manufacture.
    Return Hose
    The low-pressure hose in a power-steering system through which fluid returns to the pump reservoir after leaving the steering-gear assembly or control valve.
    A non-pressurized return hose in a pressurized fluid or air system.
    Return Spring
    Springs used on drum brakes to pull the brake shoes away from the drums when the brakes are released.
    A spring that is used to return a mechanism to its original position.
    Returnable Cylinder
    A cylinder of gas, such as oxygen, nitrogen, propane, or acetylene that can be reused.
    A DOT approved refrigerant-recovery cylinder.
    Reusable Cylinder
    A cylinder, such as a refrigerant-recovery cylinder, that may be reused.
    Rev Counter
    A tachometer.
    Rev Limit
    The maximum recommended engine speed.
    Rev Limiter
    A governor.
    A mechanical or electrical device that limits engine speed.
    Reveal File
    A small file that is pulled, not pushed, available in numerous shapes, generally curved to fit tightly crowned areas such as around windshields, wheel openings, and other panel edges for final fitting of reveal molding.
    Reveal Molding
    The metal trim that outlines an opening, depression, or raised area of an auto body.
    Reverse
    The transmission position enabling the vehicle to back up.
    To increase wheel track or tread by installing the rims backwards.
    Reverse Bleeding
    A method of purging air from a hydraulic system by forcing fluid into the system through a bleeder valve and allowing the air to escape at the master cylinder or reservoir.
    Reverse Clutch
    A multiple-disc clutch that is engaged in reverse gear.
    Reverse Elliot Axle
    A solid-beam front axle on which the steering knuckles span the axle ends.
    Reverse Flush
    A method of cleaning an engine and/or radiator by flushing in a direction opposite of normal coolant flow, under pressure.
    Reverse Flushing
    A method used to clean an engine or cooling system by flushing it in the opposite direction of normal coolant flow.
    Reverse Gear
    A transmission gear arrangement obtained from a planetary gear set when the planet-gear carrier is held and power is applied to the sun gear.
    Reverse Idler Gear
    A gear in most standard transmissions that must be meshed to obtain reverse, and that idles in all forward gears.
    A gear that transfers power in reverse only. Rotating on a separate shaft, it reverses the direction of the counter-gear motion.
    Reverse Shoe
    A term used for trailing shoe.
    Reversed Bias
    A term used when a positive voltage is applied to the N-type material and a negative voltage is applied to the P-type material of a diode.
    Reversed Polarity
    A condition that exists when battery cables are connected to the wrong terminals of a battery.
    Reversion
    The interval during valve timing overlap when both intake and exhaust valves are open and a small mist of air/fuel is forced out back through the carburetor.
    Revolution
    The movement around a center or axis such as the circling of the Earth around the Sun.
    Revolutions per Minute (rpm)
    The number of times a member, such as a shaft, makes a complete revolution in one minute.
    The rate of speed of a rotating part, such as a crankshaft.
    Rheostat
    A two- or three-terminal variable resistor used to regulate the voltage of an electrical current.
    Rib
    The tread-section element around a tire; the raised section of the tread.
    Ribbon Spring
    A spring designed to hold the sprags of a sprag-overrunning clutch at the correct angle for instantaneous engagement.
    Ribbon-cellular Radiator Core
    A type of radiator core that consists of ribbons of metal, usually copper (Cu), soldered together along their edges.
    Rich Mixture
    An air/fuel mixture having insufficient air or excessive fuel.
    Ride
    A personal car.
    An opportunity to drive in an event or series of events.
    Ride and Handling
    An indication of the degree of comfort a tire delivers to the passenger.
    A measure of the vehicle responsiveness in relation to the driver's steering actions.
    Ride Height
    The distance between the road and the bottom of a vehicle.
    Ride Shotgun
    To ride in the right front seat of a vehicle.
    Ridge
    A condition in the bores of an engine caused by piston-ring wear of the cylinder walls.
    Right-hand Thread
    A common thread for a bolt or nut that is tightened by turning it clockwise, or to the right.
    Right-To-Know-Law
    A federal law that requires all manufacturers of hazardous materials to notify and make information available to all employees, vendors, customers, and end users relative to the nature of the hazard, and to provide remedies if accidently misused.
    Rigid Axle
    A term used for beam axle or solid axle.
    Rigid Axle Suspension
    A term used for solid-axle suspension.
    Rigid Discs
    Steel plates to which friction linings or facings are bonded or riveted.
    Rigid Fifth Wheel
    A fifth wheel that is fixed rigidly to a frame having no articulation or oscillation, generally used in applications where the articulation is provided by other means, such as an articulating upper coupler of a frameless dump.
    Rigid Motor Mount
    A solid mount for attaching the motor to the frame without any provisions for vibration dampening.
    Rigid Rear Suspension
    A suspension system which has both rear wheels attached to the ends of a solid rear axle housing.
    Rigid Rear-Driving Axle
    A common rear suspension system design constructed of a central differential and tubular axle shaft housing.
    Rigid Transmission Mount
    A solid mount for attaching the transmission to the frame without any provisions for vibration dampening.
    Rim
    The outer edge of a bare wheel.
    Rim Offset
    The distance between the wheel-rim centerline and the mounting face of the disc affecting front suspension loading and operation.
    Rim Safety Ridge
    The small, metal ridge just inside the tire-bead section to retain the tire position on the rim in case of a flat or blow-out that tends to keep the bead of an uninflated tire out of the rim drop-center area.
    Ring
    A term that generally applies to piston ring, compression ring, or oil ring.
    A gasket, such as an O-ring.
    A hollow noise, such as when striking a sound brake drum.
    Ring and Pinion
    The combination of a ring gear attached to the differential and the pinion at the end of the drive shaft.
    Ring Expander
    A flexible spring-steel part placed behind certain piston rings to increase ring pressure on the cylinder wall.
    Ring Gap
    The gap between the ends of a piston ring installed in the cylinder generally 0.004 inch (about 0.1 mm) for each inch (25.4 mm) of cylinder diameter.
    Ring Gear
    The gear around the edge of a flywheel.
    A large, circular gear such as that in the final drive assembly.
    Ring Grooves
    Grooves machined around the piston wall to support the rings.
    Ring Joint
    A shock-absorber component used to attach the shock absorber to the axle and frame.
    Ring Land
    The surface of a piston between ring grooves.
    Ring Ridge
    The ridge left at the top of a cylinder wall as the wall below is worn away by piston-ring movement.
    Ring Spacing
    The width of the ring land.
    Ring-Groove Spacer
    Strips of thin metal used to fill the gap left between the piston and ring groove after the groove has been machined.
    Riser Valve
    A term used for heat-riser valve.
    Rivet
    A fastener used to hold two pieces together.
    Riveted Lining
    Linings on drum-brake shoes or disc-brake pads that are attached to their steel backing with rivets.
    RMA
    An abbreviation for the Rubber Manufacturers Association.
    RO
    An abbreviation for repair order.
    Roach Coach
    A catering vehicle.
    Road Feel
    A term that relates to the driver's ability to sense the vehicle directional control from the movement transmitted through the steering wheel by the front wheels; not so sensitive on power-steering-equipped vehicles.
    Road Horsepower
    Horsepower available at the drive wheels of the vehicle.
    Road Load
    A constant vehicle speed on level terrain.
    Road Racing
    A competition race on an irregular course simulating the variety of terrain that is found on an average public road system.
    Road-Draft Tube
    A pre-emission, control-era device for ventilating the crankcase to the atmosphere; a pipe routed under the chassis at an angle that produces a small vacuum as the vehicle travels forward. Fresh air is drawn in through a mesh filter in the oil filler cap, circulated around inside the crankcase and exhausted through the road-draft tube carrying blowby with it.
    Roadability
    The steering and handling qualities of a vehicle as it is being driven on the road.
    Roadster
    An single-seat Indycar of the late 1960s and early 1970s that resembled a two-passenger car.
    A two-passenger, open car.
    Rocker Arm
    A pivoting part in a mechanical fuel pump, one end of which rides on a camshaft eccentric or pushrod, and the other end of which pulls on the Diaphragm via a mechanical linkage, causing the Diaphragm spring to be compressed.
    A pivoting lever in the valve train of an overhead valve system which applies motion, directly or indirectly from the camshaft to open an intake or exhaust valve.
    Rocker Panel
    The sheet metal along the bottom of an auto body, beneath the doors, and between the front- and rear-wheel openings.
    Rocker-Arm Ratio
    The difference between the upper movement of the pushrod, acting on one end of the rocker arm, and the downward movement of the rocker arm acting on the valve stem.
    Rocker-Arm Shaft
    A shaft in each cylinder head on which rocker arms are arranged.
    Rod
    An abbreviation for hot rod.
    A steering arm.
    A suspension arm.
    An engine connecting rod.
    Rod Bearing
    The bearing at the crankshaft end of a connecting rod.
    Rod Big End
    The end of the connecting rod that attaches around the crankshaft.
    Rod Bolts
    The bolts used to secure the cap to the rod at the big end.
    Rod Journal
    A term used for rod bearing.
    Rod Out
    To clean a radiator.
    Rod Ratio
    A term used for rod-length ratio or rod-to-stroke ratio.
    Rod Seal
    A component used to keep oil from leaking past the piston rod and into the atmosphere during pressure conditions.
    Rod Small End
    The end of the connecting rod through which the piston pin passes to connect the piston to the connecting rod.
    Rod-End Bearing
    The spherical bearing found at the end of a suspension arm or rod.
    Rod-Length Ratio
    The center-to-center length of a connecting rod divided by the piston stroke.
    Rod-to-Stroke Ratio
    A term used for rod-length ratio.
    Roll
    To turn over and over.
    To tip or sway side-to-side.
    The motion of a vehicle body toward the outside of a turn when cornering or changing directions suddenly.
    Roll Axis
    The longitudinal axis of a vehicle defined by an imaginary line running through the front and rear roll centers.
    Roll Bar
    A tubular bar behind the cockpit of a race car to protect the driver in case of a rollover.
    Roll Cage
    A tubular, cage-like structure surrounding the cockpit of a race car to protect the driver in the case of a rollover and to add strength to the overall structure of the vehicle.
    Roll Centers
    The points at the front and rear about which the vehicle's sprung mass will roll.
    Roll Out
    The distance a race car travels in a drag-racing event at the beginning of a run before the front tires clear the stage beam and start the clock.
    Roll Steer
    The direction and amount that the rear axle may cause the vehicle to steer as it moves through its travel when the body rolls during cornering requiring the driver to oversteer or understeer to compensate for the problem.
    Roll Stiffness
    The resistance, measured in pounds per inch of spring travel, of a suspension system to the rolling of the vehicle's mass.
    Roller
    A race car offered for sale without an engine.
    A cylindrical locking element of a one-way roller clutch.
    Roller Bearing
    A bearing using rollers within an outer race or ring.
    Roller Cam
    A camshaft having a small roller at the base of each lifter.
    Roller Chain
    A timing chain having rollers that engage the gear sprockets.
    Roller Clutch
    A one-way clutch containing a number of rollers that operate by wedging on a ramp between an inner and outer race to lock up (drive) when the outer race is turned in one direction, and to slip (overrun) when it is turned in the opposite direction.
    Roller Lifter
    A valve lifter, used in some high-performance engines, featuring a roller which contacts the camshaft to reduce friction.
    Rolling Diameter
    A term used for tire rolling diameter.
    Rolling Radius
    The distance between the center of the wheel and the contact point of the tire on the ground under the weight of the vehicle.
    Rolling Resistance
    The pounds of force required to overcome the resistance of a tire to rotate.
    Rolling Start
    When cars are lined up running parade laps and a pace lap, behind a pace car, they are permitted to start with the display of a green flag.
    Rollover
    An accident in which the vehicle rolls over and over or turns upside down.
    Rolly
    A term used for roller cam.
    RON
    An acronym for research octane number.
    Room Temperature Vulcanizing (RTV)
    The trade name for a rubber-like sealing compound.
    Root Bead
    A weld bead that extends into, or includes part or all of the joint root.
    Roots Supercharger
    A mechanically driven, positive-displacement blower with hourglass-shaped rotors.
    Rope Seal
    A type of seal used on crankshafts shaped much like a small, thin rope.
    Rosette Weld
    A term used for plug weld.
    Rosin
    A sticky substance applied to the rear tires of drag-race cars for better traction off the line.
    Rotary
    The turning motion around an axis.
    Rotary Combustion Engine (RC engine)
    A four-cycle engine having a revolving triangular-shaped rotor to transfer power thrust via eccentric(s) to the output shaft.
    Rotary Diesel
    A rotary combustion engine operating on diesel principles in which the fuel injected into the combustion chamber at the end of the compression phase is ignited by the heat produced during compression, rather than by the spark from a plug.
    Rotary Engine
    A form of radial engine used in early aircraft, outmoded by the end of World War I.
    An engine with a three-sided rotor in a slightly hourglass-shaped oval chamber.
    Rotary Flow
    Torque converter oil flow associated with the coupling stage of operation.
    Rotary Oil Flow
    A condition caused by the centrifugal force applied to the oil as the converter rotates around its axis.
    Rotary Vacuum Valve
    That part of a vacuum control used to divert a vacuum signal for operation of doors, switches, and/or valves.
    Rotary Valve
    A semi-circular disc in a two-stroke engine that opens and closes the intake port.
    Rotary Valve Steering Gear
    A type of power-steering gear.
    Rotation
    A term used to indicate that a gear, shaft, or other device is turning.
    A term used for tire rotation.
    Rotator
    A device in the cylinder head that causes the valve to rotate to reduce carbon build-up.
    Rotor
    Disc-shaped component that revolves with hub and wheel. The lining pads are forced against the rotor to provide a friction surface for the brake system, so as to slow or stop a vehicle.
    In a conventional ignition system, the part that transfers the secondary voltage from the central terminal to the outer terminals of the distributor cap as it rotates inside the cap.
    The rotating part of an alternator that provides the necessary magnetic field to create a current flow.
    Rotor Face
    The flat, parallel surface on each side of the rotor contacted by the pads (linings) during stopping.
    Rotor Oil Pump
    A type of oil pump in which a pair of rotors produce the pressure required to circulate oil to the engine parts.
    Rotor-Type Pump
    An oil pump that uses two rotors, one having internal and one having external teeth to draw in and dispense oil in much the same manner as the gear-type pump.
    Roundy-Round Racing
    Any kind of oval-track racing.
    Rpm
    An abbreviation for revolutions per minute.
    RPO
    An abbreviation for regular production option.
    RTV
    An abbreviation for room temperature vulcanizing.
    RTV/Silicone
    A silicone-based RTV.
    Rubber Bumper
    Rubber stop on the car frame that prevents metal-to-metal contact when the rear-axle housing moves to its maximum upward position.
    Rubber stops positioned on or near a control arm to limit the maximum upward or downward travel of the arm.
    Rubber Manufacturers Association (RMA)
    A trade association for the manufacturers of rubber products for motor vehicles.
    Rubberized Cork
    A mixture of cork and rubber sometimes used as a gasket.
    Rubbing Block
    The insulated section of the movable breaker-point arm that contacts the breaker cam of a conventional ignition distributor.
    Rules of Motion
    A term used for Newton's laws of motion.
    Rumble Seat
    A folding seat in the rear deck of some older two-door coupes, convertibles, and roadsters.
    Rumper
    A big, noisy, rough-idling, high-performance engine.
    Run Out
    The amount a rotating object may wobble out of its plane of rotation.
    Run-On
    A term used for dieseling or running on.
    Running Board
    A flat step between the front and rear fenders to help passengers get in and out of the vehicle.
    Running Gear
    The undercarriage of a vehicle and all of the mechanical components attached to it.
    Running On
    The condition that exists when a spark-ignition engine continues to run after the ignition switch has been turned off.
    Rust
    A metal oxidation caused by moisture and oxygen.
    Rust Converter
    A liquid that can be painted over that is sprayed on bare metal to eliminate light rust and prevent other rust from forming.
    Rust Inhibitor
    A chemical added to the coolant in a radiator to reduce the build-up of rust.
    RV
    An abbreviation for recreational vehicle.
    RVP
    An abbreviation for Reid vapor pressure.
    RWD
    An abbreviation for rear-wheel drive.
    Rzeppa Joint
    A constant-velocity universal joint.
    AutoZone Logo