Every winter in Sweden, winter roadways pose problems for heavy vehicles. Steep gradients can be difficult to pass when it is slippery, which has implications also for other traffic when congestion occurs. To reduce the problems it has been discussed whether to impose a legal requirement for winter tyres on drive axle for trucks. However, there are no scientific studies of the differences in road grip that can be expected between winter and summer tyres on various winter conditions for the category of drive axle tyres. This study was therefore conducted to provide a better understanding of the issue. Since resources were limited, it was only feasible to test few tyres. One summer tyre together with three winter tyres, of which one was retreated, were selected for the tests. The tests were carried out on a test track with one type of winter road condition, namely packed snow. Traction tests on packed snow show that there can be a big difference in grip between winter and summer tyres. The difference between the tyres, however, is strongly dependent on the nature of the snow surface, so it is difficult to give general values. The least difference between the tyres was measured on very hard packed snow, where the winter tyres had 20% better grip than the summer tyre. When the snow surface was slightly softer, with occasional snowfall, the winter tyre produced over 60% more grip than the summer tyre, which implies that several vehicle combinations would be able to pass twice as steep slopes with the specific snow surface condition with winter tyre on the drive axle compared to the summer tyre. The two tested snow tracks were both relatively hard and offered good grip for all the tested tyres. We cannot from these tests predict how large the differences between the two tyre types would be on more slippery road conditions, such as ice. Theoretical calculations show that the vehicle's rolling resistance can have a major impact on how well a vehicle can climb a hill. Thick snow on the road can significantly reduce a vehicle's climbing ability. At high rolling resistance, the difference between good and bad grip on the drive tires becomes even more significant. In order to draw further conclusions about how the climbing ability of heavy vehicles in winter conditions depend on the use of winter or summer tires on the drive axle further tire tests would be required to be carried out on other surfaces, such as ice and soft snow. (Author/publisher) This report may be accessed by Internet users at http://www.vti.se/en/publications/winter-tyres-on-drive-axle-for-trucks…
Samenvatting