Wet grip braking performance on worn tyres

Abstract

"Regulatory performance parameters are always measured on new state tyres. Most of performance parameters are not showing relevant deterioration overtime, however, it is proven that Wet Grip performance is deteriorating progressively as the tyre worn out during its life. Wet grip performance deterioration means vehicle longer stopping distance on wet condition. It was also found that the wet grip index on worn tyres could not be predicted from the wet grip index on new condition tyres, at least on C1 tyres. No correlation was found. As this is a safety issue, Regulatory authorities and major stakeholders agreed to develop new test method and thresholds for wet grip on worn tyres. Basic test protocols described in UN R117.02 are observed, however, there are many specific topics that need to be addressed, such as, how to obtain artificially worn tyres fully representative of natural worn tyres, the use of reference test tyres in worn or new condition, new limits, among others. This presentation is a summary of the conclusions so far and the proposal for new Regulatory requirements is proven that Wet Grip performance is deteriorating progressively as the tyre worn out during its life. Regulatory authorities and major stakeholders agreed to develop new test method and thresholds for wet grip on worn tyres. "