Preprogrammed, permanent memory; information stored on a computer chip. Used in vehicle engine control modules and other automotive computers. Read Only Memory cannot be changed. RAM memory, like used in personal computers, can be changed and added to but is lost when power is cut.

Such chips are used in accessories like remembering specific power seat settings.

A welded steel assembly with a removable hitch which can be bolted to a vehicle frame. More sturdy and capable of greater loads than a standard bumper hitch. Necessary on modern automobiles where bumpers are usually made of plastic or another composite material. Receiver hitches are classified as class 1, class II and class III.

Class I = 1,000-2,500 lb towing capacity with 100-200 lb tongue weight.
Class II = up to 3,500 lb towing capacity, up to 300 lb tongue weight.
Class III = 3,000-5,000 lb towing capacity (up to 10,000 lb with weight- distributing hitch), 300-500 lb tongue weight.

A rugged steering design originally developed by General Motors, used commonly in nearly all trucks and sport utility vehicles; uses a special steering box and linkage design rather than a rack-and-pinion system. Inside the steering box at the end of the steering shaft is a precisely machined worm gear. An ball-and-nut assembly fits over it and moves up and down the worm gear as the steering shaft is turned. The ball-and-nut assembly contains a few gear teeth on one side which mesh with teeth on an output shaft. Thus, as the ball-and-nut unit moves up and down the worm gear, the steering box output shaft is moved and steering linkages (and wheels) are moved.

The superiority of the ball-and-nut design over previous steering box designs comes from the ingenious use of ball bearings as an interface between the ball-and-nut assembly and the worm gear, rather than using the worm gear's teeth themselves to move the ball/nut assembly. Ball bearings ride in precisely machined grooves cut into the worm gear and ball nut unit. Ball bearings essentially act as the gear teeth. What's more, there are more ball bearings than necessary and they get recirculated into tubes around the outside of the ball-and-nut assembly and back to the worm gear. The design moves the bearings around so they are not always in the same position on the shaft which dramatically spreads wear points to the surfaces of many steel balls. The ultimate result is a very rugged and long-lasting steering box design.

At the time of it's release, it was one of the greatest advances in steering technology, which other manufacturers quickly copied. Before the recirculating ball-and-nut design, vehicle steering became loose and sloppy after a relatively short amount of time.

A a keyless entry feature which uses an infrared remote control usually on the keychain to unlock the doors. Allows the driver to open the doors from a distance while approaching the vehicle. When the right button is pushed, a signal is sent from the transmitter to a receiver inside the automobile. When the signal is received, an electric current actuates a solenoid positioned near the door lock mechanism inside the doors which releases the lock.

Many keyless entry systems can also open the vehicle's windows, trunk lid and disable an alarm. Some minivans have motorized side doors which can be remotely unlocked and opened from a remote control. Also see Keyless entry.

Physical forces that a car must overcome to maintain speed such as air resistance, gravity (uphill driving) and friction from tires, engine and driveline.

In an electrical system, resistance impedes the flow of electricity.

A method of fine-tuning the length and design of an intake manifold's runners to take advantage of harmonic resonance and achieve greater engine power.

As an engine operates at high speeds, the rapid opening/closing of intake valves creates pulsing columns of air inside the intake runners. Racers and engineers experiment with various intake runner diameters and lengths to time the pulses with an intake valve's opening at a desired rpm. The effect causes more air to "rush" into the cylinder rather than would be "drawn in" under normal circumstances. Creates a supercharging effect.

A small muffler-type device found on luxury vehicles to help further reduce engine and exhaust noise. Resonators are typically used either ahead or behind the normal muffler and are tuned to reduce noise in a different frequency range than the regular muffler.

A bevel-shaped gear with no center that bolts to a rear differential and meshes with a smaller cons-shaped pinion gear.

Also, a large thin gear welded to an engine's flywheel. When the starter is engaged, it's small drive gear (pinion) pops out and turns the flywheel and therefore the engine to start the engine. Also see Flywheel and Starter drive.

See Handling, Ride, and Driveability

A recreational off-road activity carried out predominantly in the desert southwest which involves driving modified four-wheel-drive trucks and jeep-type vehicles over and around boulders, through ravines on a sanctioned trail.

Recreational drivers test their off-road driving skills and mechanical prowess by driving through "rock gardens" and famous trails such as the Rubicon (CA) whether they can make through certain trails while keeping breakage to a minimum. The activity has become so popular it has reached sport-like proportions where clubs meet for trail rides and timed events and national sponsors give out prizes. Also see Airing down, Four-wheel-drive and Central tire inflation system.

An engine component mounted at the top of an engine's cylinder heads that changes the direct of a camshaft's motion and opens intake and exhaust valves. Rocker arms are essentially levers and are used by most engines. There is typically one rocker arm for each valve. On one side of a rocker arm is a pushrod, the other side the valve stem. As the pushrod is raised (by the camshaft lobe), that side of the rocker arm is also raised which causes the valve on the other side to lower (open).

Engine's that have the camshaft mounted in the head can still use rocker arms. The pushrod is eliminated and the rocker arm rides directly on the cam's lobes. Also, see Camshaft and Lobes.

The distance between the surface of a tire's tread and the center of the wheel when rolling. The distance on some tires (bias belted) changes depending on speed, air pressure and load. To determine the distance, use the formula: R=D/6.28n.
(R=rolling radius, D=distance traveled, n= number of revolutions the tire rolled in distance D)

Rolling friction a vehicle must overcome in order to maintain speed. Main factors are flexing of tires as they roll and friction from bearings but does not include air resistance. Tires are a major contributor to rolling resistance. For this reason, switching over to radial tires (which have lower rolling resistance) increases fuel economy. A tire's rolling resistance increases with lowered air pressure and increased load. Most of the energy expended in a rolling tire is converted into heat in the tire.

Bearing rolling resistance can be lowered by using synthetic oils.

A metal, circular, disc-shaped brake component which rotates with the wheel. When brakes pads are pressed against it it slows and stops the vehicle. Used on the front of all vehicles and in the rear of vehicles equipped with rear disc brakes. Prone to warpage due to heat.

Also, a small device that mounts at the top of a mechanical ignition distributor (inside the distributor cap) which "distributes" energy to the proper spark plug. The rotor connects to the distributor cap's center electrode (cap's center wire) and passes it to an outer electrode to which the spark plug wires connect.

Also, the main rotating device in the center of a rotary motor which is driven by the expanding air (from combustion).

A low-frequency noise caused by tire tread rolling over asphalt. Aggressive tread patterns and/or rough road surfaces produce louder rumble.

Also, A noise that occurs in high-compression engines that is the result of crankshaft bending as the piston nears the top of the compression stroke. A high rate of compression increase at the top of the piston's travel causes slight warpage of the crankshaft.

1. Formed, protruding metal or fiberglass panels that mount below the rocker panels. Found on vintage automobiles. Also a popular aftermarket addition on pickup trucks. Produces a lower step (handy on tall trucks) as well as prevents rocks from being thrown onto the sides of the vehicle.