A transmission is a machine in a power transmission system, which provides controlled application of the power. ... The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. The function of any transmission is transferring engine power to the driveshaft and rear wheels (or axle half shafts and front wheels in a front-wheel-drive vehicle). Gears inside the transmission change the vehicle's drive-wheel speed and torque in relation to engine speed and torque.