The purpose of this study was to investigate how the asphalt grip during winter conditions 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, 84 tyres have been tested, of which 31 were completely new while 53 were used. The tyres have been tested on wet, salted asphalt road at temperatures around zero degrees Celsius. All tyres were tested using VTI’s mobile tyre test equipment, the BV12. These tests measured the braking and steering performance of the tyres. A subgroup of tyres (50, of which 16 were new and 34 used) were also tested with a passenger car, which measured braking performance. The winter tyres are divided into three main types: studded winter tyres, unstudded winter tyres made for Nordic conditions, and unstudded winter tyres made for central European conditions. In this report referred to as studded, Nordic and European tyres. In addition, a smaller group of summer tyres were also tested for comparison. Both premium and budget tyres were tested. Some results: • Studded tyres and unstudded Nordic winter tyres have the same are performance, for both braking and steering. This applies to new as well as used tyres. • For new tyres, the European winter tyres performs 10—13 per cent better than the two other types of winter tyres. This applies to both braking and steering. • For studded tyres and Nordic winter tyres there is no difference in brake performance between new and worn tyres. • A comparison of the steer performance between new and worn tyres were made and no difference could be seen for either studded tyres or Nordic winter tyres with respect to maximum lateral friction force. The worn European winter tyres have somewhat lower maximum lateral friction force compared to new ones. Still, they are better than the worn studded and Nordic winter tyres. • The unstudded winter tyres show a larger variation of brake performance within each group compared to the studded tyres. This was seen for both new and worn tyres. For steer performance no difference in variation was found for the different types of tyres. • The summer tyres perform as good as, or better than the European winter tyres. This applies to both new and worn tyres. It must be stressed that it is not suitable to use summer tyres at these low temperatures since they are much worse than winter tyres in icy conditions. Other studies have shown that for a winter tyre, ice and snow grip are the most important properties with respect to accident risk. The previous VTI study showed that the European tyres perform much worse than studded tyres or Nordic winter tyres on ice and snow. (Author/publisher)
Abstract