Testing and evaluating winter tyre performance has a long history and has traditionally been performed outdoor mainly by vehicle tests but also on special tyre test vehicles. One problem with this kind of testing is the weather dependence which limits the available test time under a specified surface condition. Indoor testing is a solution to this problem and at VTI a facility for this purpose has been in use since 1989. It has an about 50 m long moving flat test road that can be covered by ice in a short time. The tyre test rig is stationary but can be rotated for dynamic testing of steering characteristics. The facility is capable of testing both truck and passenger tyres at speeds up to 10 m/s (36 km/h). Test procedures for evaluating braking and steering performance have been developed and extensive tests on ice have been performed both for consumer information and for tyre development and other research purposes. The results show that there is a very large difference (more than 100 percent) between the best and worst winter tyre. Winter tyres also have to perform well on wet roads. Here the weather problem is less pronounced and outdoor road tests a competitive alternative. For passenger car tyres VTI for this purpose uses a special tyre test vehicle for braking friction tests at constant slip in the slip range from 0 to 50 percent and at 100 percent (locked wheel). A large market survey of the wet road friction characteristics of studded and non studded winter tyres as well as summer tyres in new and worn condition has recently been carried out that showed that winter tyres as well as summer tyres in new and worn condition has recently been carried out that showed that winter tyres have significantly lower performance than summer tyres (10-20 percent) but that the difference reduces with wear. The paper gives an overview of the equipment, test procedures and tyre test results for both passenger car tyres including studded tyres and the problem of functional performance requirements are discussed. (A) For the covering abstract of the conference see ITRD no E202707.
Samenvatting