Rack and pinion steering runs on the gear-set to convert the circular movement of the steering wheel in to the linear motion required to turn the wheels. It also provides a gear reduction, therefore turning the wheels is easier.
It works by enclosing the rack and pinion gear-arranged in a metal tube, with each end of the rack protruding from the tube and linked to an axial rod. The pinion equipment is mounted on the steering shaft so that when the steering wheel is turned, the apparatus spins, shifting the rack. The axial rod at each end of the rack connects to the tie rod end, which is mounted on the spindle.
Most cars need 3 to 4 complete turns of the tyre to move from lock to lock (from far to far still left). The steering ratio shows you how far to carefully turn the steering wheel for the wheels to carefully turn 
a certain quantity. A higher ratio means you should turn the tyre more to turn the wheels a certain quantity and lower ratios give the steering a quicker response.
Some cars use variable ratio steering. This rack and pinion steering system uses a different number of teeth per cm (tooth pitch) in the centre than at the ends. The effect is the steering is usually more sensitive when it’s turned towards lock than when it’s close to its central placement, making the automobile more maneuverable.
There are two main types of rack and pinion steering systems:
End remove – the tie rods are attached to the finish of the steering rack via the inner axial rods.
Centre take off – bolts attach the tie rods to the centre of the steering rack.
As steering is essential for controlling your car, it’s important to diagnose and repair any steering problems as quickly as possible.
The chances are your car has rack and pinion steering.
Thankfully, the basics aren’t hard to grasp at all: it’s about turning rotational motion into linear. When you convert the steering wheel, this turns a steering column, which rotates the attached steering shaft and a worm gear known as the pinion. This gear sits on the ‘rack’, a amount of metal with some teeth cut into it. So as the pinion rotates, the rack movements either left or right, based on your steering input.
Power steering adds a device to 1 aspect of the rack with a hydraulically actuated piston inside. A rotary valve directs hydraulic fluid to either the right or left aspect of the piston – based on the steering direction – which applies strain on the piston and reducing the effort had a need to move the rack.
The rack-and-pinion gearset does two things:
It converts the rotational movement of the steering wheel into the linear motion had a need to turn the wheels.
It provides a gear reduction, making it easier to turn the wheels.
On the majority of cars, it takes three to four complete revolutions of the steering wheel to make the wheels turn from lock to lock (from far remaining to far right).