fourwheel

Fourwheel, or four-wheel drive (4WD or 4x4), is a drivetrain configuration that can send engine power to all four wheels. This improves traction on loose, slippery, or uneven surfaces and is commonly used in off-road vehicles, trucks, and some sport utility vehicles. Four-wheel drive is distinct from all-wheel drive (AWD), which is typically designed for on-road use and may be permanent or automatically engaged, while 4WD often includes a two-speed transfer case with a low-range gear for difficult terrain.

A typical 4WD system comprises an engine and transmission connected to a transfer case, which splits power between the front and rear axles via front and rear differentials and two driveshafts. Many 4WD setups include lockable center differentials or lockable front and/or rear differentials, and some use manual locking hubs on the front wheels. 4WD can be arranged as part-time, which engages 4WD only when selected, or full-time, which uses a center differential to allow continuous 4WD operation on-road.

Historically, 4WD emerged in the early 20th century and saw substantial military use during World War II. Postwar manufacturers such as Jeep and Land Rover popularized civilian 4WD vehicles, and by the late 20th century 4WD options were common in many pickups and SUVs. In modern passenger cars, many systems described as AWD or 4WD share core principles but differ in drivetrain layouts and intended use.

Benefits of 4WD include enhanced traction, climbing ability in adverse conditions, and improved off-road capability. Drawbacks can include higher weight, increased mechanical complexity, reduced fuel economy, and higher maintenance costs compared with two-wheel-drive drivetrains.