adminthe suspension.
The suspension is the prime mechanism that joins the upper part or the body of the car and the wheels.
It also prevents your car from shaking itself to pieces. No matter how smooth you think the road is, it is a bad place to propel over a ton of metal at high speed. So we rely on suspension to absorb these shocks.
People who travel on underground trains often complain of discomfort because unlike cars, trains do not have suspensions and that is why the ride is so harsh.
Actually it is harsh because underground trains have no lateral suspension to speak of.
So as the rails deviate side-to-side slightly, so does the entire train, and the passengers are not spared from a rough ride.
In a car, the rubber in your tyre helps with this little problem. In its most basic form, suspension consists of two basic components springs and shock absorbers.
In their infinite wisdom, car manufacturers have set out to baffle us with the sheer number of different types of suspension available for both front and rear axles.
The main groupings are dependent and independent suspension types but this naming convention really only applies to traditional or analogue suspension systems.
Even independent systems are typically joined across the car by an anti-roll bar and so are not truly independent.
From about 2006 onwards, the concept of fully independent suspension systems started to appear on cars where the anti-roll bar was replaced by sophisticated computer software connected to some form of electronically controlled suspension.
There is only one type of dependent system you need to know about. It is basically a solid bar under the front of the car, kept in place by leaf springs and shock absorbers.
It is still common to find these on trucks, but if you find a car with one of these you should sell it to a museum.
They have not been used on mainstream cars for years for three main reasons: Shimmy – because the wheels are physically linked, the beam can be set into oscillation if one wheel hits a bump and the other does not.
Weight or more specifically unsprung weight. Solid front axles weigh a lot and either need sturdy, heavy leaf springs or heavy suspension linkages to keep their wheels on the road.
The third alignment simply put you cannot adjust the alignment of wheels on a rigid axis.
The MacPherson Strut is currently, without doubt, the most widely used front suspension system in cars of European origin.
It is simplicity itself. The system basically comprises of a strut-type spring and shock absorber combo, which pivots on a ball joint on the single, lower arm.
At the top end there is a needle roller bearing on some more sophisticated systems.
The strut itself is the load-bearing member in this assembly, with the spring and shock absorber merely performing their duty as opposed to actually holding the car up.
The steering gear is either connected directly to the lower shock absorber housing, or to an arm from the front or back of the spindle (in this case).
When you steer, it physically twists the strut and shock absorber housing (and consequently the spring) to turn the wheel.
Earle S. MacPherson of General Motors developed the MacPherson strut in 1947.
GM cars were originally design-bound by accountants. If it cost too much or was not tried and tested, then it was not built/used.
Major GM innovations including the MacPherson Strut suspension system sat stifled on the shelf for years because innovation cannot be proven on a spreadsheet until after the product has been produced or manufactured.
Consequently, Earle MacPherson went to work for Ford UK in 1950, where Ford started using his design on the 1950 ‘English’ Ford models straight away.
Today the strut type is referred to both with and without the ‘a’ in the name, so both McPherson Strut and MacPherson Strut can be used to describe it.
Earle MacPherson should never be confused with Elle McPherson – the Australian über-babe supermodel.
In her case, the McPherson Strut is something she does on a catwalk, or in your dreams if you like that sort of thing.
Double wishbone suspension systems
This is a type of double-A or double wishbone suspension. The wheel spindles are supported by an upper and lower ‘A’ shaped arm.
In this type, the lower arm carries most of the load. If you look head-on at this type of system, what you will find is that it is a very parallelogram system that allows the spindles to travel vertically up and down.
When they do this, they also have a slight side-to-side motion caused by the arc that the wishbones describe around their pivot points. This side-to-side motion is known as scrub.
This is the latest incarnation of the double wishbone system described above. It’s currently being used in the Audi A8 and A4 amongst other cars.
The basic principle of it is the same, but instead of solid upper and lower wishbones, each ‘arm’ of the wishbone is a separate item.
Car manufacturers claim that this system gives even better road-holding properties, because all the various joints make the suspension almost infinitely adjustable.
The trailing arm system is literally that – a shaped suspension arm is joined at the front to the chassis, allowing the rear to swing up and down.
Pairs of these become twin-trailing-arm systems and work on exactly the same principle as the double wishbones in the systems described above.
The difference is that instead of the arms sticking out from the side of the chassis, they travel back parallel to it.
This is an older system not used so much any more because of the space it takes up, but it doesn’t suffer from the side-to-side scrubbing problem of double wishbone systems.
If you want to know what I mean, find a VW beetle and stick your head in the front wheel arch – that’s a double-trailing-arm suspension setup.
So buckle up and enjoy.
Till next week . . . happy motoring.
- Fact D. Jeke is a motoring enthusiast who has attended auto shows, rallies and has written for various publications in the region for the last decade. She can be contacted via email on [email protected].
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