A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called “the pinion” engages teeth on a linear “gear” bar called “the rack”; rotational motion applied to the pinion causes the rack to move, thereby translating the rotational motion of the pinion into the linear motion of the rack.
The rack and pinion arrangement is commonly found in the steering mechanism of cars or other wheeled, steered vehicles. This arrangement provides a less er mechanical advantage than other mechanisms such as recirculating ball, but much less backlash and greater feedback, or steering “feel”. The use of a variable rack (still using a normal pinion) was invented by Arthur Ernest Bishop, so as to improve vehicle response and steering “feel” especially at high speeds.