gear reduction

A transmission (also called a gearbox) is a mechanical device which uses gears 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 petrol or diesel engines use transmissions with 5–8 forward gear ratios and one reverse gear ratio. Electric vehicles typically use a single-speed or two-speed transmission.

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