How your car works - Four Wheel Steering

It's not only Shopping Trolleys that have Four Wheel Steering. But why do you need Four Wheel Steering?

• it enables the car to be steered into tighter parking spaces
• it makes the car more stable at speed (less body roll)
• it makes the car more efficient and stable on cornering
• it makes the car easier and safer to change lanes when on motorways

Is it fitted to every car?
Presently, Four Wheel Steering is only fitted to certain Japanese and prestige cars, but with the advancing development in electric steering systems, the future may see more cars fitted with rear wheel steering.

How does it work?
Four Wheel Steering works by incorporating a steering mechanism (similar to the one at the front end) into the rear of the car and controlling it electronically or mechanically. When the front wheels steer at certain angles, the rear wheels are adjusted to various positions to provide a better method of controlling the car when turning.

An example of rear wheel steering is that of the Fork-Lift truck that can turn in very tight spaces because of it's ability to steer from the back end. It is not an easy vehicle to drive and certainly takes some getting used to in order to steer properly.

Obviously, it would not be practical to have rear wheel steering on it's own, but combine the two and you have a car that is able to steer more precisely and accurately. Unlike the aforementioned shopping trolley!

When does it work?
The rear wheels are turned in the same direction or opposite direction as the front wheels, depending on the speed the car is travelling and the angle to which the steering wheel is turned.

This all happens very quickly and almost unnoticeably to the driver but allows the car to follow a much tighter line of turning into a corner.

When the steering wheel is turned to a certain pre-set angle and the car is moving at a pre-determined speed, then the rear wheels will turn in the same direction as the front ones. Over that steering angle or speed then the rear wheels will either move to a straight ahead position or turn in the opposite direction to the front ones.

What makes it work?
The system is controlled either by a series of driveshafts or it is driven electronically depending on the vehicle type. There are many components installed in the underside of the car to control the steering mechanisms fitted at the rear. One of these components is a steering gearbox, similar to the front end steering assembly to alter the rear wheel angles.

Sounds complicated. What if it goes wrong?

If the system was to develop a fault, a fail-safe device will lock the alignment of the rear wheels in a straight-ahead position so that the car can be steered safely.

The four wheel drive system is a complicated set-up and requires expert knowledge and special tools to service and repair. If the system develops a fault then immediate action is required to ensure that the car is not in a dangerous condition to be driven on the road.

Your local Unipart Car Care Centre will be able to diagnose and carry out repairs to the system, but be warned, parts are likely to be on the expensive side.

Caring for your steering: Making sure that the car goes where you point it!

Steering (front and/or rear):

• Keep a check on the steering components to ensure that they are in good condition. The steering components are checked once a year for the MOT test but if you find that there is freeplay or excess movement on the steering wheel then take the car to your nearest garage for diagnosis.
• Wear in rubber mountings for the steering rack, subframe or suspension joints can also drastically affect your car's handling, especially when cornering. These items are checked at the yearly MOT test.
• Constant 'kerbing' will damage the suspension and steering components and will also disturb the pre-set steering angle geometry of the car. If the edges of any tyres show signs of wear then your local garage can set the correct wheel alignment.
• Please remember that worn or damaged steering parts can be very dangerous. If any problems exist with the steering of your car, it would be advisable to take it to your nearest garage for immediate repair.

Shock Absorbers:

• If the car shows signs of bouncing or weaving across the road when either in a straight line or when cornering then replace the shock absorbers.
• If the car starts swaying at speed or a knocking noise (bottoming out) when going over bumps in the road you could be looking at a new set of shock absorbers.
• Always replace shock absorbers as a complete axle set, e.g. both front ones or both rear ones as a pair.