Picture 1 shows a wishbone fitted with two rubber bearings. One of them is it's own mounting, and the stabilizer is connected to the other. The rubber bellows on the suspension strut (see picture 2) are almost more important still. They come into action, when the spring-travel has been used up. At this point a gentle transition to the rigid system is important, otherwise the car would be uncontrollable.
These are genarally replaced together with the pivot points of the shock absorbers, Indeed, they should still be checked (see picture 3). With a torsion beam axle (see picture 4) the bearing bracket (2) and the guide bearing (1) are the only direct connections to the car body. If there is play or deterioration here, then something must be undertaken, and quickly.
Here you see a not quite typical, easily repairable wishbone. Apart from the individually changeable ball-head, we can also see the individually changeable bearing. If the suspension rests in a separate frame, in relation to the bodywork (see picture 5), then this is also very well damped. Picture 6 shows the more complex assembly-carrier of an off-road vehicle (VW Tuareg). Trucks have even less elasto-kinematics on board (see picture 7), possibly the only the bearings and the stabilizer-guidance.
Actually, one can understand the three-dimensional movement of a wheel, if the kinematics of the suspension are known. If it's a rear wheel, then it has a certain path when compressing and rebounding. As far as the front wheel is concerned, there is also the steering to be considered. Herewith, all the possibilities are described, if only the wheel or the suspension did not have rubber bearings.
So, all the additional wheel-movement possibilities belong under the heading 'elasto-kinematics'. We'll notice, that the bearing-points are not always only filled with rubber, but have a more complex form. If a standard car is modified for racing purposes, then these bearings are replaced anyway by metal ones which have no additional play at all.
In addition, there is the trend, towards using low cross-section tyres which lower the vehicle, causing the suspension to be harder and harder. The comfort that the tyres alone had to provide in the past, is nowadays, to a large extent, taken over by the elasticity of the suspension. Almost as a side effect, a dampening of the vibrations and also road noises to the interior has also been achieved. Indeed, the suspension also provides elasticity itself, e.g., through distortion.
Larger differences in the chassis would also be measurable during the influence of braking and strain. Elasticity is often used here to improve the cornering qualities of a certain axle construction. It's clear, that in this case a purely geometrical representation is simply not enough. What a blessing it is, that there are computers and software that can simulate something like this.
On top of everything else, the deformation of the bodywork itself must also be considered. It has become increasingly safer as far as crashtests are concerned, but that doesn't mean that it hasn't become more elastic in certain areas. This can also be the result of weight-reduction, which in the case of the suspension, is twice as useful, as long as the unsprung masses are reduced.
To be better able to estimate the value of elasto-kinetics, perhaps a look at one of the most frequently used front suspensions, the McPherson strut, would be a good idea. Basically, at the bottom of the wishbone, rubber bushings take the place of the joints. Thereby, such a wishbone has to cover considerable angles, depending on the amount of spring travel. Apart from this, up to the point of having to be replaced, they're maintenance-free.
When installing the rubber-joints, attention must be paid to the unstrained situation when the suspension is in the normal position. The wishbone itself, because of it's huge lateral strain, attempts to support itself as broadly as possible, it must however, allow the wheel a sufficient turning angle. Because this angle is more acute when the wheel is turned inwards than it is when turned ouwards, the wishbone support can be further toward the front than the rear.
One can see that higher forces are at work on the strut, because compared with a normal shock absorber, the piston rod has a distinctly greater diameter. Nonetheless, one still allows a certain amount of inflexion here, which can also result in the lack of responsiveness. Even ball-joints are not free of a certain amount of deformation, only an unacceptable increase in weight could diminish this decisively.
It's not without reason, why modern vehicles may not be lifted off their springs before an axle alignment is undertaken. This is a difficult task for the constructor, to bring this, in itself an adverse factor, into a possibly, positive whole. In the past, it is said that there have been vehicles (BMW 02), which by coincidence, have been given a special suspension.
Actually, the supension seems to be a sector, where test-driving offers an abundant increase of experience. And this, even though of course, there is any amount of software for the calculation of rigidity (FEM) and there are also testbenches for finished axles and also for complete vehicles, from whose data-banks the various demands can be generated.
Thus, one can understand, without actually drivng the vehicle, whether the elasticity in the wheel guidance, has a positive influence on the qualities of the suspension or not. For example, sometimes, even today, it is wrongly maintained that, the front-wheel-drive has toe-out and the rear-wheel-drive, fundamentally toe-in. This may have been the case when suspensions had no elastic components. Nowadays, one must actually speak of static (where the parameters are precisely described) and dynamic toe-in.
If, at this point, the reduction of costs and of weight are mentioned, one has still forgotten one important advantage, namely the oscillation reduction. Rubber has, as opposed e.g., a steel spring, the positive characteristic of causing oscillations to fade out, fortunately, before any negative reaction can be built up. This may however, be even more important as far as the mountings of the engine-block are concerned. 01/14