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Most vehicles use two-wheel drive (2WD), where engine power is sent to the front or rear wheels. Front-wheel drive is used in most cars, wagons, minivans, and the two-wheel-drive versions of car-based SUVs because it's space-efficient. It allows the car to have a smaller engine compartment, leaving more room inside for passengers and cargo. It's also better than rear-wheel drive in slippery conditions because there's more weight on the front wheels and they pull rather than push the car along the road. This helps prevent the rear end from sliding sideways in slippery conditions.

Rear-wheel drive places less demand on the front wheels, allowing them to be used primarily for steering. It's commonly used on pickups and traditional truck-based SUVs that are designed to handle heavy-duty chores like towing. But rear-wheel drive is also popular on sports cars and high-performance sedans because of its contribution to good handling.

Traction control, available on late-model vehicles, helps maximize traction at the drive wheels by preventing wheel spin. It's particularly useful when accelerating on a wet, snowy, or icy surface. If no drive wheel has grip, however, traction control won't help. In wintry conditions, we've found that a two-wheel-drive vehicle with traction control can have more difficulty getting up a slippery slope than one with all- or four-wheel drive.

All-wheel drive (AWD) feeds power to all four wheels. It provides maximum forward traction and is especially helpful in slippery conditions and when driving over moderate off-road terrain. AWD is also helpful in rapidly changing conditions or when driving on a road with intermittent snow and ice. Its lightness and compactness makes it the system of choice for wagons, some minivans and pickups, and most car-based SUVs.

Although four-wheel drive (4WD) and AWD are designations that are often used interchangeably in advertising and brochures, the major difference is that 4WD incorporates low-range gearing, which helps in more challenging off-road conditions, such as traversing rocks or deep water, or tackling steep off-pavement hills. The majority of 4WD-vehicle owners, however, never come close to needing this capability.

Modern 4WD systems are either full-time, which means they can stay engaged all the time, or automatic, where the vehicle switches between two- and four-wheel drive depending on the driving conditions. But many pickups and some truck-based SUVs use part-time 4WD systems, which require the driver to manually shift between two- and four-wheel drive, limiting the vehicle's ability to provide optimum traction when conditions becomes slippery. In addition, these vehicles can't be driven on dry pavement when in 4WD mode without running the risk of severe drivetrain damage. Keep in mind that AWD and 4WD systems add considerable weight to a vehicle, compromising fuel economy.

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