The term four-wheel drive
-like vehicles that may allow the driver to manually switch (sometimes with an automatic option) between two-wheel drive mode (if available) for streets and four-wheel drive mode for low traction
conditions such as ice, mud, snow, slippery surfaces, or loose gravel.
(AWD) is often used to describe a "full time" 4WD that may be used on dry pavement without destroying the drivetrain, although the term may be abused when marketing a vehicle.
AWD can be used on dry pavement because it employs a center differential
, which allows each tire to rotate at a different speed. ("Full-Time" 4WD can be disengaged and the center differential can be locked, essentially turning it into regular 4WD. On the other hand, AWD cannot be disengaged and the center differential cannot be locked.
) This eliminates driveline binding, wheel hop, and other driveline issues associated with the use of 4WD on dry pavement. With vehicles with more than four wheels, AWD means all wheels drive the vehicle, to varying degrees of engagement, while 4WD means only four of the wheels drive the vehicle continuously.
Identical drivetrain systems are commonly marketed under different names for upmarket
branding and, conversely, different drivetrain systems are commonly marketed under the same name for brand uniformity. Audi
with the xDrive
, and Volkswagen
, for example, can mean either an automatically-engaging "on-demand" system with a Haldex Traction clutch
, or a continuously-operating permanent 4WD system with a Torsen