DIFFERENTIALS
The power from the engine is ultimately directed through the transmission to the
drive wheels by means of the differentials. Differentials also allow the drive
wheels to turn at different rates of speed, making for ease of turning. Some
performance cars and 4WD vehicles have a Posi-Traction, or lockup differential.
It is designed specifically for locking the drive wheels together for maximum
traction on acceleration.
Differential Locations in Different Vehicles
Front-wheel drive is used on most passenger cars today. This design weighs
less, eliminates the need for a driveshaft and transmission tunnel (creating more
interior space), and places the engine over the drive wheels (maximizing tire
traction).
Rear wheel drive is often chosen for its simplicity and good handling
characteristics. Placing the drive wheels at the rear allows ample room for the
transmission in the center of the vehicle and easy access for service. Traction in
inclement weather is a problem because there is virtually no weight over the rear
wheels. To counter this effect, people put sand bags in their trunks during the
winter. In performance cars with high-output engines, this design is desirable
because the extra weight in the rear of the car (coupled with setting up the rear
suspension to transfer vehicle weight downward on the rear wheels) results in
better drive wheel traction on hard acceleration off the line.