Assignment

Without exagerating, one could say that the wheel was the most important technical invention of all time. All the more regrettable is, that apparently it had to be re-invented several times! Indeed, in approx. 2000 BC the Egyptians probably didn't know, that the the wheel was already known by the Sumerians in 3500 BC. However, it is possible that they never really knew what to do with it. We only know that they had it because it is illustrated in reliefs from this period.

Function

Some say that the wheel was developed from a slice of a tree trunk. However, as you can see in the 1st picture, this is not at all suitable. Only then, when the wheel is made up of three parts (picture 2) and is given an axle, can it convert sliding- into rolling friction. This is why wheel bearings with rolling elements were later installed. However, first of all wood remained the material, part of the time very nice spokes were were produced, to maintain the same firmness and at the same time saving weight. As early as in the Roman times, iron materials were put to use. An iron band was spanned around the outside of the wheel, and in the hub, together with some sort of lubricant, made the bearings more durable. Because of the bad roads the load was sprung against the axles using leather belts.

In 1846 the inflatable tyre was first invented by William Thomson, it was however soon forgotten. In the same century, the Irishman, John Boyd Dunlop, developed the pneumatic tyre. Actually it was only intended for his son's tricycle. A linen cloth was wound around an airtight rubber tube. If the tube needed to be repaired, the cloth had to be removed, layer for layer. At that time, there were neither motor cars nor the low, chain driven bicycles that we know today. Thus, the application was reserved for a few of the coaches and the high-rise bicycles (Penny-farthings).

With the development of the bicycle, the pneumatic tyre was created, offering an alternative to the uncomfortable solid-rubber tyres. Indeed, at that time hard rubber was also being used as the final layer between the road and the wheel. It could only be mounted using a great deal of force in the shops where preferably, cars were repaired, the village blacksmith. To make this invention actually usable for vehicles, the tubing had first to be separated from the covering, which had to have cotton threads worked into it to strengthen the material. Together with Goodyears invention, the vulcanisation, the first treadless, beaded-tyre was created, in the beginning, only for motor cars.

These tyres, with their pressure of at least 5 bar, were a real plague for the motorists. They had to be checked before almost every journey and, often enough did not survive the procedure. Up to 50 tyre-changes were perfectly normal in the course of a long motor car race. Therefore it was considered a blessing when finally, in 1905, the removable wheel-rim was brought out.

At that time, there were of course, neither tyre-codes nor any suitable standardizations. Slightly damaged tyres could possibly be repaired on the spot, if the damage was greater, they had to be sent away, for an unknown period. New tyres were only purchased in exceptional cases. The price of tyres, depite the many other repairs and the short inspection intervals, were the highest cost factor when owning a motor car, sometimes they were even higher than the cost of the petrol.

To increase their running performance to five times what it was, from 1920 onwards, low pressure tyres were introduced. More than thirty years later one succeeded in developing the tubeless tyre through an addition sealing on the wheel-rim and in the inside of the tyre. These were simpler to mount and above all, under normal driving conditions, were also safer, because, e.g., the friction between inner-tube and the tyre was cancelled out. One disadvantage as far as mounting was concerned, was that, particularly later as radial tyres, there had to be a hump on each side, to prevent them from slipping into the drop-center when cornering or when a stronger pressure-loss took place.

At the same time, the first radial-tyre was invented by Michelin, indeed, it could only assert itself widely much later. In this case, the tread-surface was, through a stronger carcass, which sometimes had steel-wire threads worked into it, much more stable than the side-walls. This promised less rolling friction and more stability when cornering. The lower flexibility was compensated for by the vehicles spring suspension. This is how it then stayed, except that the tyres are now wider and their cross-section has become lower. 01/12