Rolling resistance is due to the interaction between road surface and tires and forms part of the driving resistance that a vehicle needs to overcome to move forward. Those of the road surface properties that are seen as most important for rolling resistance are macro texture and unevenness along the road. But water and snow on the road surface also contribute to the rolling resistance. Precipitation that remains on the road means that the wheels need to be driven through and displace water or snow, and this leads to increased resistance. In addition, water cools more efficiently than air, which has an effect on the behavior of the tires as their viscoelastic properties are temperature dependent. The tires work at a lower temperature in the presence of precipitation, which in itself increases the resistance.
Speed, temperature and water depth are the explanatory variables often found in the literature to describe the effect on rolling resistance due to water on the road surface. It has been shown that rolling resistance increases with increasing speed, increasing water depth and decreasing tire temperature. The results indicate that the effect can be significant, with measurements showing an increase of 30 to 40 percent of the rolling resistance coefficient depending on the speed and thickness of the water film. However, the literature in the area is relatively limited, and the reason for this is probably linked to the difficulties that exist in measuring and modeling the rolling resistance effect in water. These difficulties are due to, among other things, measuring the depth of the water film and the temperature of the tires and that the temperature of the tires needs to be stable during measurements.
Studying the impact of snow on rolling resistance also involves some difficulties in that there are many different types of snow with varying properties and behavior during deformation. Data available is also limited and the relationships are not sufficiently developed so that they can be fully used to describe the behavior of the snow with respect to deformation and load. The complexity of the impact of snow on rolling resistance means that a combination of theoretical calculations and field studies is needed to determine the values of the components included. However, some studies have been carried out that aim to explain the impact of snow, both theoretical and via field measurements. The explanatory variables often used are snow depth, snow density and tire contact surface with road surface. In general, the results show that snow has a large effect on the resistance and that it should therefore be considered, especially in areas where snow remains on the ground for a long time.
Översättning av: VTI rapport 971. "Effekten på rullmotstånd av vatten och snö på vägytan" 2018