A car powered by an internal combustion engine moves by transmitting the engine's rotational movement to the wheels via the transmission, driveshaft and differential. Front-wheel drive cars do not require a driveshaft, but rear-wheel drive and four-wheel drive cars use driveshafts to transmit power to the rear wheels.
The system that transfers power from the engine to a car's wheels is called the drivetrain. The exact configuration of a drivetrain varies depending on which of the car's wheels power the car. The most common model found in many vehicles today is the front-wheel drive system. Another system, common in older vehicles, but also found in many sports cars, is rear-wheel drive. Lastly, some cars, especially those designed for off-road driving, use all four wheels to move the car.
In a front-wheel drive car, the front-mounted engine powers the front wheels, which pull the car forward. A component called the "transaxle" combines the functions of the transmission and differential and distributes the engine's power to the wheels using halfshafts. Since the front wheels must steer and drive the car, they use constant velocity, or CV, joints that maintain smooth power distribution even when wheels are turned completely to the left or right.
In a classic rear-wheel drive car, power is transmitted from a front-mounted engine to the rear wheels, which push the car forward. The transmission is directly attached to the engine, which is longitudinally mounted, and a long driveshaft connects it to the differential, which is located at the rear axle. The differential then transfers the engine's power to the rear wheels.