Automobiles are steered by turning the front wheels, although a few automobile types have all-wheel steering. Most steering systems link the front wheels together by means of a tie-rod. The tie-rod insures that the turning of one wheel is matched by a corresponding turn in the other.
When a driver turns the steering wheel, the mechanical action rotates a steering shaft inside the steering column. Depending on the steering mechanism, gears or other devices convert the rotating motion of the steering wheel into a horizontal force that turns the wheels.
Manual steering relies only on the force exerted by the driver to turn the wheels. Conventional power steering uses hydraulic pressure, operated by the pressure or movement of a liquid, to augment that force, requiring less effort by the driver. Electric power steering uses an electric motor instead of hydraulic pressure.