Auto Terms P

Pearl Paint

A type of paint that is similar to metallic paint, but instead of minute metal particles it uses mica. Mica is a kind of semi transparent, crystalline mineral that absorbs and reflects light in prismatic fashion. This gives a dramatic, multi-dimensional effect to the paint. Sometimes called "pearl coat."

Pinion

A gear with a small number of teeth designed to mesh with a larger geared wheel or a rack. Used in rack and pinion steering and the differential ring and pinion.

Pitch

The up and down movement along an imaginary axis between the front and rear of a vehicle. Often during hard braking, the vehicle's nose will "dive" or pitch down in front. During acceleration the back end will "squat" or pitch down in the rear.

Piston

A partly hollow cylindrical part closed at one end, fitted to each of the engine's cylinders and attached to the crankshaft by a connecting rod. Each piston moves up and down in its cylinder, transmitting power created by the exploding fuel to the crankshaft via a connecting rod.

Planetary Gears

A gear set, generally found in automatic transmissions, in which all of the gears are in one plane, grouped around each other like planets around the sun. The central gear is called the "sun gear."

Plies

The layers of cord, fiberglass, steel or structural fabric that make up the tire carcass and reinforcing belts.

Ply Rating

A measure of the strength of tires based upon the strength of a single ply of designated construction. An eight-ply rating does not necessarily mean the tire has eight plies, but rather that the tires has the strength of eight standard plies.

Pound-Feet (LB.-FT.)

Pound-feet measure twisting force or torque. Generated by the engine, torque is the "push" that sets a vehicle into motion and accelerates it. Specifications charts usually include the maximum torque the engine can develop, and the RPM at which it is generated (such as 345 lb.-ft. @ 3200 RPM).

Power Band

A subjectively defined RPM range over which an engine delivers a substantial portion of its peak power. The power band usually extends from slightly below the engine's torque peak to slightly above its horsepower peak.

Powertrain

A name applied to the group of components used to transmit engine power to the driving wheels. It can consist of engine, clutch, transmission, universal joints, drive shaft, differential gear, and axle shafts. Powertrain components are matched according to driver needs such as high torque, fuel economy, or convenience.

Predetonation

The undesirable "knock" or "ping" that occurs when the ignition of the air-fuel mixture occurs before the ignition spark. Also known as "pre-ignition".

Pushrod

A general term for any rod that transfers force in compression. In a conventional overhead valve layout, pushrods are used to transfer reciprocating motion from the cam followers to a more distant part of a valve train, typically the rocker arms. Pushrods are eliminated in overhead camshaft designs.

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Auto Terms Q

Quarter Panel

A sheet metal panel that covers the area from the rear-door opening to the taillight area, and from the bottom of the surface to the base of the roof, or from the headlamp area to the front-door opening, and from the bottom of the surface to the base of the hood.

 

Quartz Halogen Headlamps

A headlamp bulb having a quartz envelope holding the tungsten filament and filled with an inert gas containing iodine or another of the five halogen gases. The gas serves to remove the tungsten deposits from the bulb wall and redeposit them on the filament, preventing blackening of the bulb surface and reduction of light output. This kind of cycle requires very high filament operation temperatures which necessitates the use of quartz instead of glass. These lamps produce more lighting power per watt of electrical power than standard sealed beam headlamps.

Rack and Pinion Steering

A steering gear in which a pinion on the end of the steering shaft merges with a rack of gear teeth on the major cross member of the steering linkage. When the steering wheel is turned, the pinion gear turns, moving the rack to the left or right, thus steering the wheels.

Residual

A conservative projection of the market value of a vehicle at the end of a lease. Residual values are provided by major auto manufacturers or independent companies that specialize in auto valuation.
A higher residual value will lower the monthly payment. However, the vehicle must be resalable at the residual amount or the lessor will lose money. Conversely, adjusting the residual too low will increase the monthly payment and may make the lease payment unattractive. Adjustments to residual may be made for excess mileage or wear and tear.

Resonator

A small auxiliary muffler that assists the main muffler in reducing exhaust noise.

Ring-and-Pinion Gear

Any gear set consisting of a small gear (the pinion gear) which turns a large-diameter annular gear (the ring gear). Used in rear-drive differentials (rear ends) to transfer power from the driveshaft to the axle and wheels.

Rolling Radius

Tire-rolling radius is the distance from the center of the wheel to the road. Static radium applies when the vehicle is standing still. Dynamic rolling-radius described wheels in motion. The latter is used to measure tire revolutions per mile and is usually slightly higher than static radius.

Rolling Resistance

This is motion resisting force that is present from the instant the wheels begin to turn. On normal road surfaces, rolling resistance decreases with increased tire pressure and increases with vehicle weight. Rolling resistance can also be affected by tire construction and tread design.

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Auto Terms S

SAE

Acronym for the Society of Automotive Engineers. A professional organization that sets standards for measuring horsepower and torque and for many automotive products such as fasteners, lenses, and lubricants.

Sealed Beam Headlamp

A one piece, hermetically sealed headlamp in which the filament is an integral part of the unit and the lens itself is the bulb. Sealed beams are relatively inexpensive and when one burns out or the lens cracks, the whole unit is replaced.

Spoiler

An aerodynamic device, normally on the rear of the vehicle, that changes the direction of airflow in order to reduce lift aerodynamic drag. A spoiler either reduces drag or create a downward force on the car. It is called a spoiler because it "spoils" the normal air flow over the car.

Springs, Torsion Bar

A long straight bar that is fastened to the frame at one end and to a control arm at the other. Spring action is produced by a twisting of the bar.

Steering Ratio

A predetermined ratio of the steering gears. Usually, the lower the steering ratio, the quicker the response.

Stroke

The distance the piston travels from bottom dead center to top dead center within the cylinder.

Strut

The main support member in a MacPherson suspension system. The strut also serves as the shock absorber.

Supercharger

Supercharging is the compression of an engine's intake charge above atmospheric pressure by means of an air pump driven by a crankshaft. This is not to be confused with a turbocharger which is an air pump that is exhaust driven.
A supercharger can provide boost faster than a turbo and over a much broader engine rpm range. The disadvantages of supercharging are higher power demands, more mechanical noise and more complex control requirements.

Suspension System

Includes springs, shock absorbers/struts, and linkage used to suspend a vehicle's frame, body, engine and drivetrain above the wheels.

Tachometer

An instrument for measuring the speed of the engine crankshaft in revolutions per minute (RPM).

Throttle-Body

Throttle-Body Fuel Injection is a type of Electronic Fuel Injection which positions the injector(s) centrally in a throttle-body housing. This housing contains a valve to regulate the airflow through the intake manifold.

Timing

Timing refers to the crankshaft angles at which the valves open and close and at which time the ignition system fires the spark plugs.

Tire Ratings

Tires are rated by load capacity, size and speed capacity. For example, a P225/50VR16 printed on the side of the tire means:

• P = P-Metric (Passenger Type Tire)
  
• 255 = Section Width (255mm)
  
• 50 = Aspect Ratio (tire height/section width)
  
• V = Speed Rating
  
• R = Type of Ply (Radial)
  
• 16 = Wheel Diameter (16 inches)
  

Tire and wheel dimensions are the first point of information in any discussion of size and capacities. Among the other terms used to describe tires are: tread, shoulder, carcass, sidewall, bead seal, bead seat, tire diameter, aspect ratio, speed rating and section width.

Toe In

The amount by which the front of a front wheel points inward or outward. A slight amount of toe in is usually specified to keep the front wheels running parallel on the road by offsetting other forces that tend to spread the wheels apart.

Torque

A force that produces a twisting or rotating motion.

Torque Converter Clutch

An electronically controlled lockup clutch that is automatically engaged at certain speeds to eliminate the slip between the torque converter's input and output, thereby improving fuel efficiency and performance.

Torque, Engine

Engine torque is the amount of twisting effort exerted at the crankshaft by an engine expressed in foot-pounds of force. A foot-pound represents the force of one pound acting at the right angle to the rotating crankshaft at distance of one foot in length.

Torque Rating

A measure of the engine's power capability, whereby the amount of twisting or rotating effort being exerted on the crankshaft is expressed in lb.-ft. of force. Torque is the force that gets the weight of the vehicle moving, making it an important consideration in trailering.

Torsion Bar

A long straight bar fastened to the frame at one end and to a suspension part at the other. In effect, a torsion bar is merely an uncoiled spring, and spring action is produced by twisting the bar. The main advantage of the torsion bar over the coil spring in the front suspension is the ease of adjusting the front suspension height.

Traction Control

Traction control helps provide smoother, more controlled acceleration by reducing the amount of wheel spin during reduced traction conditions. Traction control utilizes the vehicle's anti-lock braking system and is usually activated only at low vehicle speeds.

Trailing Arm

A rear suspension element consisting of a lengthwise member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end.

Transaxle

A transmission and differential combined in one integrated assembly, eliminating the need for a separate connecting drive shaft. This configuration is typical in front-wheel-drive vehicles.

Tuned Intake and Exhaust Systems

Intake and exhaust systems that increase the flow of intake charge into and out of the combustion chambers by varying the length, shape, or diameter of the component.

Tuned-Port Fuel Injection

Tuned-Port Fuel Injection is almost identical to Multi-Port Fuel Injection, except that tuned runners are used to channel air to the cylinder heads. This results in increased airflow to the cylinders.

Turbocharger

Rotary compressor or pump that pressurizes engine intake air. It is driven by the flow of exhaust gases. The increased pressure forces more air into the cylinder than it could normally draw, allowing the engine to burn more fuel and in turn produce more power.

Unibody Construction

A type of body construction that doesn't require a separate frame to provide structural strength or support for the vehicle's mechanical components. Also called "unitized."

Universal Joint

A joint that transmits rotary motion between two shafts that aren't in a straight line.

Auto Terms V

Valve

A device that can be opened or closed to allow or prevent the flow of a liquid or gas from one place to another. Most internal combustion engines use intake and exhaust valves to allow fuel/air mixture into the cylinders and to exhaust burnt gases. Some engines have four valves per cylinder, which increases total valve area for increased efficiency and performance.

Valve Lifter

The cylindrical component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates, opening and closing an intake or exhaust valve. Virtually all modern valve lifters are of an hydraulic design that uses a cushion foil to promote quiet operation.

Valve Train

The collection of parts that make the valves operate, allowing fuel intake, compression and exhaust. Includes the camshaft(s) and all related drive components, and the various parts that convert the camshaft's rotary motion into reciprocating motion at the valves.

Auto Terms W

Weight Distribution

That portion of the total weight of a vehicle, including equipment and payload, that will be supported by each axle and tire. Proper distribution of total vehicle weight is critical to the service life of components such as the frame, axles, springs, bearings, and tires and therefore one of the most important requirements in selecting the right truck for your customer's particular job.

Wheelbase

Distance, center to center, from front axle to rear axle. Wheelbase is important because it indicates available body length and weight distribution between front and rear axles.

Wholesale Value

The price, based on auction results or retailer trade reports, that a retailer expects to pay for a vehicle.

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