A vehicle's drive wheel is the wheel and tire assembly that actually pushes or pulls the vehicle down the road. In a rear-wheel drive vehicle, the drive wheel is located in the rear of the vehicle. In front-wheel drive applications, the drive wheel is situated in the front of the vehicle. In an all-wheel drive type vehicle, the drive wheel is actually a pair of wheels with one front wheel and one rear wheel receiving power on a constant basis and the other wheels receiving power as the on-board computer deems necessary.
On a street driven vehicle, power is typically applied to only one side of an axle. This is made possible through the use of an open differential. The open differential applies power to the tire that most needs it while shifting the power from side to side when a vehicle is turning a corner. In this situation, the power is applied to the inside drive wheel as the vehicle negotiates the corner, thereby allowing the outside wheel to coast, or free wheel. This is done due to the requirement of the outside tire to turn faster than the inside tire in a cornering situation.
In certain high-performance applications, both sides of an axle are designated drive wheels and turn at the same speed at all times. This is made possible with a locked differential or posi-traction, as it is commonly called. The positive traction differential places the power to both sides of the vehicle's drive axle to provide the utmost traction available at any given time. While this set-up works well for off-road applications, when used on a street-driven vehicle, the outside tire chirps and slides as the vehicle negotiates corners.
In front-wheel drive vehicles, the drive wheel is also the steering tire. In less-than-favorable driving conditions, the drive wheel can spin and create an ill-handling vehicle. The spinning and slipping tire is unable to gain the traction needed to turn the vehicle when the steering wheel is turned. Traction is usually regained by reducing the amount of throttle that is being applied, and the vehicle will then turn.
By controlling the amount of power that is being directed toward the vehicle's drive wheel, traction, and subsequently driving ability, can be vastly improved. Any wheel that is sliding and spinning out of control hinders the operator's ability to control the vehicle. Maintaining proper traction will allow the vehicle to be much more easily controlled.