Most vehicles use two-wheel drive (2WD), where engine power is sent to only one pair of wheels. Many of today's cars, minvans, and even some car-based crossover SUVs use front-wheel drive (FWD) because of its cost-effective, space-efficient design, thereby eliminating the need for an intrusive driveline hump that can dominate the foot space in the back seat. In slippery conditions, the FWD configuration benefits from weight balanced over the front wheels—used for both traction and steering.
Rear-wheel drive (RWD) is commonly found on pickups and truck-based SUVs, as well as sports cars and high-performance sedans. For trucks, RWD allows the use of bulky, heavy-duty components, and it provides better traction with a heavy load. On a performance car, rear-wheel-drive improves handling by spreading the weight more evenly over the two axles and by reducing demand on the front wheels, allowing them to be used primarily for steering but RWD provides less traction on slippery roads.
All cars and light duty trucks sold in the U.S. starting with the 2012 model year have electronic stability control, which along with traction control significantly improves winter driving, especially for RWD vehicles. Even so, we've found that all- and four-wheel-drive systems provide superior traction in slippery conditions.
Like the name implies, all-wheel drive (AWD) feeds power to each corner. It provides maximum forward traction during acceleration; it is especially helpful in wintry conditions and when driving over moderate off-road terrain. Most AWD systems deliver power primarily to one set of wheels, front or rear; when slippage is detected, power is shifted to the wheels that have the most traction. AWD systems are especially helpful in rapidly changing conditions or when driving on a road with intermittent snow and ice. It is commonly used for most car-based SUVs, as well as many cars and minivans. (See our list of best AWD vehicles.)
Although four-wheel drive (4WD) and AWD are designations that are often used interchangeably in advertising and sales literature, there is a difference. Generally, 4WD is optimized for severe off-road driving situations such as climbing over boulders, fording deep water, and tackling steep hills with loose, low-traction surfaces. Most 4WD systems have high and a low gear range, the latter used to increase low-speed climbing power. Some have differentials (which allow left and right wheels and front and rear axles to turn at different speeds) to be locked for maximum traction.
Modern 4WD systems are either full-time, which means they stay engaged; automatic, where the vehicle automatically switches between two- and four-wheel-drive mode; and part-time, which require the driver to manually shift between two- and four-wheel drive. Vehicles with a part-time system shouldn’t be driven on dry pavement when in 4WD mode, which could risk damage to the vehicle's drivetrain.
Aside from serious off-road enthusiasts, most drivers never come close to needing the capability that 4WD systems provide over and above AWD systems.