Most modern cars use a rack and pinion mechanism to transmit the steering angle to the wheels. This system works in harmony with independent front suspension and the steering rack forms the centre section of a three-piece track rod. The steering wheel is connected to a steering column, which in turn is connected to the steering rack.
When the steering wheel is rotated, this effort is transmitted through the steering column, which is connected to the steering rack's pinion gear. The pinion gear is in constant mesh with the steering rack's inner rack gear and drives the rack in the opposite way to the steering wheel angle. This movement causes the track rod length to decrease on one side and increase proportionally on the other, which then turns the steered wheels in the desired direction.
Due to the positioning of the track rods connected to the steered hubs the wheels are able turn at differing angles, which greatly improves cornering and stability. Once cornering is complete the steering need to return to the centre position quickly, the steering will self centre due to the swivel axis inclination, which is the angle between the wheel and the axis of the fixed swivel joints.
When a vehicle is travelling at normal road speeds the steering feels light and easy to use, however when a low speed manoeuvring is required the steering becomes very stiff and difficult to turn. Manufacturers have overcome this by fitting power assisted steering. Traditionally this is achieved with a hydraulic pump that is driven by the engine via a belt, which applies fluid pressure to a hydraulic ram built into the steering rack. A valve controls the fluid pressure within the rack effecting one side of the ram when turning providing hydraulic assisted steering. More recently manufacturers are employing electric power steering to cars were an electric motor replaces the engine driven pump, or in some cases the motor acts directly on to the rack. The benefits for the electric systems are that there is no power loss from the engine due to drag from a pump and more steering data can be gathered for sophisticated steering, braking and stability systems.
Many modern steering wheels are fitted with an air bag, a supplementary restraint system (SRS), which will be deployed when a front-end impact has occurred. Crash sensors that detect impact and sudden deceleration send a message to the SRS control unit that then send a signal to the air bag igniter unit and the air bag will be fired off. Another safety feature is that the steering column is designed to collapse in the event of a severe front-end crash. This ensures that the vehicle cabin remains intact and prevents the driver from being impaled by the steering column.