How Car Steering Works

Pointing the car is only half the job. The other half is telling the driver what the road is doing.

Apart from starting and stopping, probably the most obvious function required of a motor vehicle is that it must be able to be directed in varying degrees to the left and to the right. So what, other than changing direction, is required of the steering system?

Feedback from the road

One of the most important functions is the transmission of feedback from the steered wheels to the driver. This feedback gives a good indication of the condition of the road surface being driven on, and also an indication of the state of the front tyres.

Rolling over a frozen surface will produce far less noise and vibration than a good road surface; the steering will almost certainly feel much lighter and will become rather vague. A tyre operating at a reduced pressure, or one that is almost flat, will induce drag, make the steering feel unresponsive and cause the vehicle to wander. Correct interpretation of the above via the steering may well prevent an accident caused by loss of control.

Where the steering process starts

Starting at the steering wheel, a component usually made up of a metal alloy structure covered with a trim which provides bulk and grip for the driver, driver input is transmitted via a shaft through to the steering mechanism. The shaft itself not only has the task of rotating, but also must either collapse or move away from the driver in a crash situation. This is normally achieved by a combination of joints and crushable sections.

The added advantage of the inclusion of these joints is that they allow the steering shaft to exit the passenger compartment at angles more easily connectable to the steering mechanism; the positioning of this mechanism may well be dictated to some extent by the design of the bodyshell and subframes.

Six mechanisms, one common choice

There are six main types of steering mechanism: worm and sector, screw and nut, recirculating ball, cam and peg, worm and roller, and rack and pinion. By far the most common system used on modern cars and light commercial vehicles is the rack and pinion. This system is simple in operation, lends itself easily to the addition of power assistance, is relatively lightweight, and has little or no maintenance requirements other than routine inspection.

What to keep an eye on

All in all, the steering mechanism itself is low maintenance. However, it is important that regular inspections are made in the area of basic wheel alignment, commonly referred to as tracking. Faults in this area normally manifest themselves as irregular tyre wear or poor handling. On a less frequent basis the owner may wish to have a more comprehensive steering and suspension check done of the castor and camber angles.

All of these factors will have an effect on one other desirable feature, that of self centring. It becomes very tiresome if the driver is forced to manually return the steering wheel to the straight ahead position after every turn; correct steering geometry is vital for this to happen.