rack and pinion

Rack and pinion steering uses a gear-set to convert the circular movement of the tyre in to the linear motion required to turn the tires. It also provides a gear reduction, therefore turning the wheels is easier.
It works by enclosing the rack and pinion gear-set in a metal tube, with each end of the rack sticking out from the tube and connected to an axial rod. The pinion gear is mounted on the steering shaft to ensure that when the tyre is turned, the apparatus spins, shifting the rack. The axial rod at each end of the rack links to the tie rod end, which is attached to the spindle.
Most cars need three to four complete turns of the tyre to move from lock to lock (from far to far remaining). The steering ratio shows you how far to carefully turn the tyre for the tires to carefully turn a certain amount. A higher ratio means you should turn the tyre more to carefully turn the wheels a particular amount and lower ratios supply the steering a quicker response.
Some cars use variable ratio steering. This rack and pinion steering system uses a different number of the teeth per cm (tooth pitch) in the centre than at the ends. The result is the steering is definitely more sensitive when it is switched towards lock than when it is near to its central position, making the car more maneuverable.
There are two main types of rack and pinion steering systems:
End remove – the tie rods are mounted on the end of the steering rack via the inner axial rods.
Centre remove – bolts attach the tie rods to the center of the steering rack.
As steering is essential for controlling your vehicle, it’s vital that you diagnose and restoration any steering problems as quickly as possible.
The chances are your car has rack and pinion steering.
Thankfully, the fundamentals aren’t hard to grasp at all: it’s all about turning rotational motion into linear. When you switch the steering wheel, this turns a steering column, which rotates the attached steering shaft and a worm equipment known as the pinion. This gear sits on the ‘rack’, a amount of metal with some teeth cut involved with it. So as the pinion rotates, the rack movements either left or correct, depending on your steering input.
Power steering provides a device to one side of the rack with a hydraulically actuated piston inside. A rotary valve directs hydraulic fluid to either the right or left part of the piston – based on the steering direction – which applies pressure on the piston and reducing the effort needed to move the rack.
The rack-and-pinion gearset does two things:

It converts the rotational movement of the tyre in to the linear motion needed to turn the wheels.
It provides a gear reduction, making it easier to turn the wheels.
On the majority of cars, it takes 3 to 4 complete revolutions of the tyre to make the wheels turn from lock to lock (from far still left to far right).