Rubber mixture:

The rubber mixtures of car tyres differ very widely in order to optimise the tyres for certain seasons and their average temperatures. And the search for the optimum tyre continues. Every year, the tyre manufacturers test thousands of rubber mixtures in order to develop new car tyres. Test tyres are made of these rubber mixtures, the properties of which are then examined on the tarmac.

The rubber of a tyre has many tasks to accomplish – on the one hand it has to absorb shocks (in physical terms, this property is based on the ability of the material to store energy) and on the other hand it has to cling to the road surface. So the ideal material should be a compromise between optimum adaptation to the road – a soft material – and an endurable material which won't disintegrate at the first emergency braking. For this purpose it is important to know the actual size of the area where the rubber has contact with the tarmac, and which forces are in effect on the material. A tyre which is being pushed over the tarmac during a full braking, is subject to entirely different forces than a tyre resting immobile on the road surface. Apart from the unevenness of the road, there are also the interior frictions within the material to consider. It should also be taken into consideration that the soft rubber mixture within a tyre tends to harden with age. The rubber becomes brittle and traction diminishes.