Automotive Terms - M

MacPherson Strut

A MacPherson strut is a unit that includes a damper or shock absorber cartridge inside a large, long metal spring. MacPherson struts are used over the front wheels of most front-drive cars. Replacement of MacPherson strut cartridges requires a spring compressor.

Make

The manufacturer of the vehicle (BMW, Chrysler, Honda).

Manual Transmission

A transmission that varies the power and torque through a foot pedal controlled clutch and a floor-mounted or steering-shaft-mounted gear selection lever.

Minimum Ground Clearance

The distance between the ground and the lowest point of the vehicle chassis (usually the axle). A vehicle can drive over any object shorter than its minimum ground clearance.

Moonroof

A window-type opening in the roof of the car that can open or tilt up or down. See Sunroof.

Muffler

The exhaust system device in the tailpipe that reduces engine noise. Some vehicles have more than one muffler along the tailpipe.

Multi-Link Suspension

Independent suspension controlled with several link arms that restrict undesired motion of the suspension for a smoother ride and more precise handling.

Multi-Port Fuel Injection

An electronic fuel-injection method that uses individual injectors to spray fuel directly into each intake port, bypassing the intake manifold. Also called multi-point fuel injection.

Automotive Terms - O

Overdrive

A transmission gear with a ratio below 1:1, which improves fuel economy by reducing engine revolutions per minute at highway speeds. On a five-speed manual transmission, the fourth and fifth gears are overdrive. On a four-speed automatic transmission, the fourth gear is overdrive. When an overdrive gear set is engaged, the output shaft turns at a higher rate than the input shaft, reducing engine revolutions at cruising or highway speeds.

Overhead Cam (OHC)

The camshaft is on top of the cylinder head on overhead-cam engines. Single overhead-cam (SOHC) engines have a single cam above the cylinder head. Dual overhead-cam (DOHC) engines have two cams above the cylinder head. All overhead-cam engines are also overhead-valve (OHV) engines, which means the intake and exhaust valves sit atop the cylinder head.

Oversteer

Occurs when the rear tires lose adhesion under cornering. In motorsports, this is also called loose. Oversteer can lead to a spin if the driver doesn't reduce acceleration. See also Understeer.

Automotive Terms - P

Pick-up

The type of truck with an open cargo bed behind the closed cab.

Pinion

A type of gear that has small teeth that mesh with other, larger gears.

Piston

The heavy, cylindrical metal shaft within each engine cylinder that travels up and down to turn the crankshaft, compress the air and fuel mixture for combustion and expel exhaust gases.

Power Steering

A steering system that uses a separate motor or engine power to reduce the effort necessary to turn the front wheels.

Power-to-Weight Ratio

The maximum power output of the vehicle per unit mass. The higher the ratio, the more powerful the vehicle. In comparing several vehicles, this can be a better measurement than engine horsepower or torque because it considers the weight variable. In other words, a car that seems to have a powerful engine but is also heavy may have less get-up-and-go than a vehicle that has a similar or less powerful engine but also weighs less.

Powertrain

The combination of engine and transmission.

Power Plant

Another name for a vehicle's engine.

Projector-Beam Headlights

A headlight that uses a spherical reflector to tightly control the light beam. The bulb or light source directs the light inward, toward the reflector at the back of the headlight assembly, which then projects it forward from the vehicle. These lights are more powerful, accurate and expensive than standard sealed-beam and halogen headlights, and are generally found on sport and luxury models.

Pushrod

A metal rod that transmits the motion of the camshaft.

Automotive Terms - R

Radiator


A device that cools the liquid in the cooling system by allowing it to circulate through a series of water channels, which are exposed to air ducts.

Automotive Terms - S

Shock Absorbers


Devices located near each wheel to cut down the vertical bouncing of the passenger compartment on the springs after the wheels go over a bump or the car stops short. Shock absorbers also improve handling on rough road surfaces. See also suspension system.

Automotive Terms - T

Traction Control


A feature that senses when one wheel is spinning faster than the others. It may automatically apply the brakes, cut off power to that wheel, and/or reduce acceleration to improve traction and maintain stability.


Transmission


A box of gear wheels that allow your car to move forward and backward with varying amounts of power to meet a variety of driving situations. Manual transmissions are operated by means of a clutch and gearshift. Automatic transmissions are driven by hydraulic pressure.

Automotive Terms - V

Valves


Metal devices that open and close to allow fuel and air to enter the combustion chamber and exhaust gases to leave it. Operated from the camshaft by means of valve lifters, push rods, rocker arms, and overhead camshaft lobes, the valves can be adjusted with feeler gauges so that they open and close at the proper times. (These adjustments can’t be made to valves that are operated by valve lifters). See also exhaust valve, intake valve, timing belt, timing chain.