Automotive Terms Dictionary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Pascal
After Blaise Pascal, French (1623-1662). The pascal, like the pund per square inch, or the kilogram of force per square meter, is a unit of pressure.

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.

Pneumatic Tire
Flexible, hollow rubber forming the outer part of the vehicle wheel and inflated by air pressure.

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.