The purpose with this study was to investigate how the road grip on ice and snow for different types of winter tyres degrade by age and degree of wear. Special focus was on the comparison between studded and unstudded winter tyres. In total, 77 tyres have been tested, of which 27 were completely new while 50 were used. The tyres have been tested on smooth ice and packed snow. All tyres were tested using VTI’s unique tyre test equipment: the tyre test facility on ice, and the BV12 on snow. These tests measured the braking and steering performance of the tyres. A subgroup of tyres (42, of which 12 were new and 30 used) were also tested with a passenger car, which measured braking and acceleration performance. The tyres are divided into three main types: studded winter tyres, unstudded winter tyres made for Nordic conditions, and undstudded winter tyres made for central European conditions. In this report referred to as studded, Nordic and European tyres. Both premium and budget tyres were tested. Ice grip: • For the new tyres, the studded tyres generally have much higher performance compared to the two studless types, for which the Nordic type in turn is much better than the European. From the test performed in VTI’s tyre test facility, the estimated braking distance were in general 30 percent longer for the Nordic tyres compared to the studded. For the European tyres the braking distance were 55 percent longer compared to the studded ones. • By comparing used and new tyres, it is clear that the performance decrease is the largest for the studded tyres, about 20—25 percent. The performance decrease for the two studless types is about 10 percent. It shall however be pointed out that in spite of this, the used studded tyres are general superior to used studless winter tyres of both Nordic and central European type. • The used European winter tyres have in general really bad ice grip, and performs on level with two summer tyres that were also tested. • On really slippery ice, the studded tyres increase their performance advantage. In addition, for the unstudded winter tyres, the difference between new and used tyres seems to disappear. The tests on really slippery ice show that in these conditions even very worn studded tyres can perform considerably better than new studless winter tyres of Nordic type. • Premium tyres have in general better ice grip compared to budget tyres, both for new and used tyres. Snow grip: • The difference between the different types of winter tyres is smaller on snow than on ice. • For the new tyres, the Nordic tyres in general have a slightly better grip than the studded tyres. However, this difference can only been for the budget tyres. For new premium tyres, no difference in snow performance could be seen between studded and studless tyres of Nordic type. The new studless tyres of European type have lower snow grip compared to the two other types of winter tyres. • By comparing used and new tyres, it is clear that the performance decrease is the largest for the European tyres, about 20—25 percent for all performance measures: braking, steering an acceleration. The performance decrease for the studded tyres is within 10—15 percent, and for the Nordic tyres a few percent less. • For the used tyres the Nordic tyres in general have the best performance, even if the difference compared to studded tyres in not very large. The European tyres on the other hand, have much worse performance, with a braking distance that is 20 percent longer compared to the used Nordic tyres. • For studded tyres the premium tyres in general have a clear performance advantage compared to the budget tyres. For studless tyres the difference between premium and budget is not that evident. (Author/publisher)
Abstract