Gear box 3D model

A transmission (also called a gearbox) is a mechanical device which uses a gear set—two or more gears working together—to change the speed or direction of rotation in a machine. Many transmissions have multiple gear ratios, but there are also transmissions that use a single fixed-gear ratio.

Most currently-produced passenger cars with gasoline or diesel engines use transmissions with 5–8 forward gear ratios and one reverse gear ratio. Electric vehicles typically use a fixed-gear or two-speed transmission with no reverse gear ratio.