Four-Wheel Drive

Four-wheel drive, also called 4×4 ("four by four") or 4WD refers to type of a vehicle, specifically one with its drive-train capable of providing torque to all wheel ends of a two-axled vehicle simultaneously. It may be full-time, or on-demand, and is typically linked via a transfer case which provides an additional output drive-shaft, along with additional gear ranges.

When a four-wheeled vehicle has torque supplied to both axles, this is described as "all-wheel drive" (AWD). However, "four-wheel drive" typically refers to a set of specific components and functions, and/or intended offroad application, which generally complies with modern use of the terminology.

4WD gives advantage as improved traction and handling. Also it is able to transmit torque to all four wheels. But on the other side it has disadvantage as high initial cost, more weight and requires special service and maintenance.

Components of 4WD includes:

Transfer Case- Transmits power from the transmission to front and rear drive shafts.

Drive Shafts- Connect the front and rear differentials.

Universal Joints- Used to connect axle to wheel hubs.

There are two types of 4WD systems:

Part time 4WD: In this system only operates two wheels until driver commands four wheel drive operation.

Full time 4WD: This system constantly provides power to all four wheels. These systems typically do not have "Low" operating range.