In vehicles, a transmission is a device that helps apply the engine’s rotational force to the drive wheels. A transmission may use fixed-ratio gears or variable-size pulleys to step the speed of rotation up or down to allow the vehicle to travel at a broader range of speeds. A transmission may also change the direction of rotation, such as when a driver selects a forward or reverse gear. Transmissions may rely on the driver to select the desired gear ratio, or the transmission may make the selection automatically. See also manual transmission, continuously variable automatic transmission, CVT.
