AWD

All-wheel drive (AWD) is a drivetrain configuration that sends power to all four wheels of a vehicle. It is designed to improve traction and stability on low-friction surfaces such as snow, rain, or ice, and to enhance handling in certain conditions.

AWD systems can be full-time, distributing torque to all wheels at all times, or automatic/torque-sensing, which directs power to the wheels with the most grip as needed. Common mechanisms include a center differential that splits torque between front and rear axles; a center clutch or viscous coupling that modulates torque transfer; and electronically controlled systems that vary distribution and may offer torque-vectoring to bias power toward a particular axle or wheel. Some systems are designed to be rear- or front-biased and adjust based on driving input and conditions.

AWD is distinct from four-wheel drive (4WD), which typically uses a transfer case and may include a low-range gear intended for off-road use and harsh conditions. 4WD is often driver-selectable and can be optimized for rugged terrain. AWD differs from front-wheel drive (FWD), where only the front wheels receive power. In many AWD setups, the center drivetrain component can permit different wheel speeds to reduce drivetrain binding on dry pavement, while still delivering torque to both axles when needed.

Advantages of AWD include improved acceleration and cornering grip in adverse conditions and on varying surfaces. Disadvantages can include added weight, higher cost, increased mechanical complexity, and potentially reduced fuel economy. Tire condition and compatibility are important in AWD systems, since mismatched tires or worn tread can affect performance and drivetrain wear.

AWD is common in passenger cars, crossovers, and some performance vehicles. Notable implementations have been developed by manufacturers such as Subaru and Audi, among others, with varying degrees of automation and torque distribution.