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All Tests

History - Wunibald Kamm 3

He did not have much time until the preparations for war also had an impact on the research work or the lack of raw materials, e.g. that of rubber, made certain projects appear to be of little use. As you can see, we want to focus on the contact between tires and road surface. Whereby the roadway was initially represented by a much too small drum.

This was then soon replaced by the 'Rollende Landstrasse', a steel strap with which pressure could be exerted from below on the contact area and thus different wheel loads could be simulated. The development of tires was still in its infancy at the beginning of the 1930s, often a lot of rubber under high pressure, at least already provided with a profile.

Kamm and his team first demonstrated that the rolling resistance of low-pressure tires increases with speed because of the increasing flexing work. The pressure in the tire also plays a role here, but leaves little comfort as the internal pressure increases. After all, a variable control system with air supply via the hub had already been realized while driving.

Reasonably accurate temperature measurements were also taken, mind you on the rotating tire. Were these too high resulted in the protector becoming detached. But the main aim of the investigations was how one would cope with the low-pressure tires on the new highways currently under construction, first when braking, then when accelerating.

The easiest way to calculate the force flow was to use full braking. This could also be determined as a function of the wheel load through tests taken from other publications. The main problem when switching to low- pressure tires turned out to be the lack of lateral stability due to the much thinner sidewalls.

This led to the so-called slip angle, which is formed between the position of the wheel and the actual direction of travel. This led to the so-called slip angle, which is formed between the position of the wheel and the actual direction of travel. The larger it is, the stronger the tendency to follow the position of the wheel. If you record the slip angle on the wheels of the front and rear axles separately, you can use the values to diagnose oversteering or understeering behavior. Furthermore, the stabilizing effect of a larger front than rear axle load resulted.

Now we come to the famous Kamm's friction circle. The picture above is not entirely accurate, because the conceptual model assumes a lateral stiff wheel. At rest and with a certain load, the force directed against friction is 3, which is necessary to pull it while standing on the floor in a certain direction, the same in all directions.

With 1 as the driving power and 2 as the lateral guiding force, within the circle that documents the equality of the frictional force in all directions, there is a dependence of the two variables on each other, which is to be shown by the parallelogram of forces. More driving power reduces the ability to lateral guidance and a lot of necessary lateral guidance allows the drive wheels to spin more easily.

Incidentally, it does not matter whether we look at the drive or the braking forces. The results are equal and almost easier to verify. Only assume a vehicle (without ABS) whose steering you fully turn during emergency braking. The vehicle will not follow it, but will continue to move in a dead straight line beyond the turned front wheels.

One can imagine that the thought of an ABS control system known to us today arose here in order to maintain maneuverability. There are already patents from that time, but the mechanics were not suitable for the required fast control. Of course, tests were also carried out with wheels that were lateral not stiff and, of course, a decrease in lateral guidance was found the softer the tire or its sidewalls were.

If the Kamm friction circle is rather aimed at winding country roads, the tests with simulated cross winds are absolutely suitable for motorways. After all, Bernd Rosemeyer lost his life in a record attempt in 1938, presumably due to a cross wind. Here again the thesis of the center of gravity being further ahead proves to be a better protection. Anyone who has ever driven a T2 at Mistral will fully confirm this.

In 1940, the Kamm employees Riekert and Schunck created a well-regarded mathematical registration of the forces and moments occurring on the chassis. The two lanes of a vehicle were replaced by a single one with the same wheel position at the front and rear. Of course, this was further developed later, e.g. also towards computer simulation.

We can only mention the rest here briefly:

Truck driving stability when towing a trailer
Vibration problems with overrun brakes
Dreaded oscillating motions when towing a trailer
Lightweight construction through self-supporting body
Aerodynamics and air resistance
Measurements for this in the wind tunnel
Assessment of the VW3 prototypes
Establishment of a fuel test laboratory
Emissions tests

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