Glossary

2WD or 4 x 2 — Terms for two-wheel drive. In front- or rear-wheel-drive vehicles, a differential along the axle drives this pair of wheels and adjusts the speed at which these wheels turn while cornering. Basically, the other set of wheels go along for the ride. The regular passenger cars tend to have front-wheel drive, while many sports cars and luxury models have rear-wheel drive.

4WD or 4 x 4 — Terms used to describe a vehicle with power that goes to all four wheels. There are many different types of four-wheel drive. The basic systems are full-time, part-time and permanent.

All-wheel drive or AWD — These systems power all four wheels usually full-time for improved traction and handling. There is no two-speed transfer gearbox to provide a low-range set of gears. In the past, these systems were used exclusively on passenger-cars, but AWD is now crossing over into sport utility vehicles.

Continuously variable transmission — A belt or chain running between two pulleys transfers power from the engine to the driveshaft. As the pulley driven by the engine slowly expands, the pulley driving the wheels contracts, thus continually varying the ratio between the two.

Stability control — A sophisticated traction-control system that improves grip on the road in situations where traction is compromised by either cutting out engine power or pulsing the brake on a spinning wheel, or by doing both, to help send power to the wheel with the most grip.

Supercharger — An air pump driven by the engine, via a belt or gears. By forcing more air (and thus fuel) into the engine's combustion chambers, it increases horsepower.

Traction control — A system that automatically cuts or reduces the throttle if it senses that a drive wheel is spinning as a result of excessive power application or a slippery surface.

Transfer case — In vehicles designed for four-wheel drive, a secondary gearbox or gear system capable of delivering power to both axles at the same time. Such a system is desirable where extreme off-road capability is needed, because it offers both high and low gears. The high-gear range is used for normal driving on-road, while the low-gear range is essential for extremely rough off-road conditions where more power and traction is needed for all four wheels and the vehicle is traveling slowly.