Undercarriage 2

A part of the car-buying procedure is, and rightly so, the test driving. However, before it comes to a test drive, an important item is, at least for the customer, the climbing into and sitting in the new car. It is otherwise unexplainable, why everyone wants to sit in the cars on the showroom floor or those shown at trade fairs, even though they aren't allowed to drive the car an inch.

By the way, even touching the object of your desire must be cleared up beforehand. Justifiably, there are signs decorating nearly all classic cars, telling people please not to touch them. Let's remain for the moment at the trying out of the seats. Although the smell of a new car really has nothing to do with our subject, it does matter. If one climbs in, and then feels slightly uneasy, getting him/her to buy the car is going to be a hard job.

Imagine that you are sitting in this car. Was it easy to get into? Do you fancy the fact that it's that narrowly built and that you have to follow an exact procedure to get in at all? Or do you feel cramped in a tailor-made environment? Do you check the access to, and the feeling given by the rear seats? For the time being it doesn't matter, first of all, you're sitting up front.

What about the feel of the steering wheel and what's it like to touch the buttons and switches on the dashboard? How well can the driver's seat be adjusted? If it tweaks or pinches anywhere, then optional seating comfort could be your next question. What's the all-round visibility like? Make an adjustment to the interior rearview mirror. It takes a while, before everything fits. If you wish to photograph the car at a trade fair, without any one sitting in it, an enormous amount of patience is required.

In the meantime, one has several options when looking at the instrument display: Through or over the steering wheel or in the middle of the dashboard. I'll bet, that by now, you've already tried to turn the steering wheel and have pushed the pedals, although this won't tell you much. I think at this point, we can end the seat-test and let the photographer get a few good pictures.

I hope we can agree, that subjectivity and emotions can by no means be excluded when buying a car, actually, it's more the opposite. Nevertheless, let's try to do the test-drive as objectively as possible. What we would really appreciate, would be that the car reacts spontaneously to the 'commands' coming from, e.g., the steering wheel. At the same time, the car should not give a nervous impression, the last thing we want, is to be surprised by unexpected behaviour.

If we exclude the self-called racing drivers, what we expect, is relatively neutral handling when cornering. It is very important, that you are warned early if the car starts going into a skid. We would actually prefer a somewhat lower speed maximum in such a situation, than a higher speed where the car could break away abruptly. Indeed, should it come to this, we would also rather have a bit of understeer than oversteer, because in a situation like this, one instinctively tends to turn the steering wheel a bit more anyway.

Now it's time, to go a bit deeper into our definition of a good suspension, without slating the present equipment. The sprung masses should remain as neutral as possible, regardless of how bad the roads are. On the other hand, the unsprung masses should also be damped, however, it is even more important, the wheels always maintain contact with the road. Under certain circumstances, this could mean a lot of up and down movement of the wheels underneath a stoically neutral car body. If the wheels start to hop, then it's high time that something should be done about it.

A certain amount of feedback is important. In Europe an 'insensitive' steering is considered disagreeable, except when parking the car. The same thing counts for reaching the cornering limits, in this case an acoustic warning is reassuring, but not when travelling normally, where e.g., rumbling is undesirable. Humpy roads should be damped rather a bit less than too much. In the latter case, one could easily speak of threatening sea-sickness.

The amazing thing is, that almost everyone has their own ideas about good handling, although they can't actually describe what they mean. Some like it more comfortable, others emphasize the handling, sometimes also when they're talking about large, rather unwieldy vehicles. A great deal of development has gone into curbing the larger rolling angles that are typical of such large vehicles. At the same time of course, the physical limits should not be diminished.

The perfect testing scenario doesn't really fit into this description at all. One must be able to carry out perfectly standardised test trials, where even the smallest adjustments will show up in the results. Up to now, one is still dependant on test-drivers. Nevertheless, driving manoeuvres must be determined.



This type of standardization has been around for quite awhile. One particularly well known example, is the so-called moose-test. The parcours, where the curves, the length and the width are standardized, is driven through at a speed of 50 km/h. Actually, the achieved speed is one measure of being suitable for the test. It can be found in a number of variations, e.g., as a VDA (Union of Automobile Industries)- and an ISO (International Organisation for Standardization)- test, also with the prescribed wet road run-through. As you can see by this example, a standardization of the suspension testing that covers as much as possible, is difficult to realise:
- There are an incredible amount of driving situations.
- The condition of the road, results in a number of possibilities.
- The steering- braking- and acceleration procedure must be precisely laid out.
If you will, give it some thought, due to the possible combinations, the respective possibilities have to be multiplied.

The biggest problem seems to be, that sometimes the test-driver's interpretation of the guidelines is imprecise. Apart from the recently, so propagated, autonomous driving, robots which can drive cars have been around for some time. Also the loading of the vehicle must be fundamentally determined. Testing should be done with both lighter- and heavier loads on the roof, loads in the front and rear and those which are longer than the car, should also be considered.

An interesting point is e.g., that new tyres are used for the test-runs, they must however, have been 'run-in' for about 200 km. Take note, when next buying tyres. Then the standards to be achieved, are still to be fixed, They will certainly be different for a low-lying coupé, than for a high-top van. Apart from the height of the centre of gravity here, the aerodynamics also play a role. By the way, reasonably comparable results can be achieved when driving in a circle with an exactly fixed steering wheel position and at a fixed speed.

At least, one can show fairly correctly, how individual changes affect the suspension. Thus, less wheel-load, more track-width, wider tyres, a softer stabilizer, more toe-in and a bit more negative camber, will more than likely improve the cornering stability, i.e. will make less tilting-angle necessary when cornering. Of course, with less wheel-load, the mass which builds up a centrifugal force, is meant, this is due to the proximity of the centre of gravity.

Should this axis be pressed onto the road by aerodynamic downdraft, this again, will improve the lateral guidance. It is also not necessary to make specific adjustments like e.g., increasing the toe-in. Elasticity can, e.g., also produce changes in the caster. If e.g., the lower wishbone, because of it's softer mountings, is pressed towards the rear, the caster-angle will decrease and the lateral guidance will again, be slightly improved.

With or without the help of elasticity, the braking- and acceleration momentum can also affect the lateral guidance of an, in this case, driven axle. We all know about the unwillingness of vehicles when braking, to follow the direction targeted by the steering. All-wheel drive vehicles have also recently been given a torque distribution which adapts itself to the slip-angle. 02/14