Rack and pinion

A rack and pinion is a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a flat bar – the rack. Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel.

Alternatively the rotation of the pinion that is mounted on a locomotive or a railcar will engage the rack between the rails and pull a train along a steep slope.

The rack and pinion arrangement in vehicle steering is commonly found in the steering mechanism of cars or other wheeled, steered vehicles. This arrangement provides a lesser 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 was invented by Arthur E Bishop, so as to improve vehicle response and steering “feel” on-centre, and that has been fitted to many new vehicles after he created a hot forging process to manufacture the racks, thus eliminating any subsequent need to machine the form of the gear teeth.