In a motor vehicle, the term rivetrain or powertrain refers to the group of components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, driveshafts, differentials, and the final drive (drive wheels, caterpillar track, propeller, etc.). Sometimes "powertrain" is used to refer to simply the engine and transmission, including the other components only if they are integral to the transmission. In a carriage or wagon, running gear designates the wheels and axles in distinction from the body.