By. Suzzanne Nickell
One of the biggest questions that floats around in our minds whenever purchasing a vehicle, is should I purchase a vehicle with AWD or 4WD, and what are the differences?
In AWD this system works to get power to the wheels with the most traction by splitting power between the front and rear axels on the center differential and the individual wheels by way of the front and rear differential.
This is useful either in slippery conditions when different wheels might be getting different amounts of grip from moment to moment. The Mercedes-Benz E63 AMG is a perfect example. It is now sold only in AWD in the U.S. because its power can overwhelm the traction of the rear wheels alone.
True 4WD systems use a transfer case, which is like a two-speed transmission that bolts to the back of the regular transmission. Upon engaging 4WD, a transfer case locks an output shaft powering the front axle to the transmission’s output, mechanically locking the front and rear axles together. No matter what happens, the engine’s power splits at a 50/50 ratio front to back.
The primary problem with an auto-locking 4WD system is that it’s either on or off; it can’t vary torque like an AWD system does. This means that a part-timer will act like a RWD truck while navigating a turn, so it won’t have the on-road handling prowess of an AWD vehicle. However, automatic 4WD is perfect for situations where you’re likely to encounter a mixture of dry pavement and mud, dirt, grass, ice or snow. Otherwise, you have the option of leaving it in RWD or locking it into 4WD.