The study concerning the contact between a tyre and a road surface was conducted by means of an experimental multifactor investigation. It was attempted not only to determine the effect of variables such as type of road surface and speed on the skid resistance but also interaction effects. In the first phase the first and second-order factors were separated. The second phase served to determine the numerical influence of the road surface characteristics and the speed on the size of the brake and side way forces. It was found possible to compile a mathematical relation incorporating the contribution of the macro-roughness and micro-roughness of the road surface and also of the speed to the brake and side way forces. In the third phase a similar mathematical relation was drawn up for truck tyres. Car and truck tyres were compared by reference to the results. A main feature is that with truck tyres the values of the available brake forces are about a factor two lower than with car tyres. Among the characteristics of the road surface, the micro-roughness has mostly considerable influence on the skid resistance. The influence of the macro-roughness of the road surface counts heavily almost exclusively at high speeds. Finally, recommendations are made for official measures, with emphasis on standards to be met by the micro-roughness and macro-roughness of road surfaces. (A)
Abstract