This field study was designed to compare to what degree various proportions of studded and studless winter tyres in traffic affect the roughness and polishing of packed snow and ice road surfaces.
Test cars equipped with studded and studless winter tyres drove around a test track according to the designed procedure. The main straight section of the track had five lanes, each with a different proportion of cars with studded tyres: 100%, 75%, 50%, 25% and 0% of the respective lane traffic. The remainder were cars with studless winter tyres. An additional reference lane had no traffic. Each lane included sections of hard snow and ice with subsections for constantspeed, braking and acceleration (figure 1). The lanes were driven 642 times. The ambient temperature was approximately 0°C during the tests.
The development of average friction from all 6 measuring spots can be found in figures 2 and 3. The averages in figure 2 are based on braking friction measurements from vehicle with studded tires and averages in figure 3 from measuring vehicle with studless tires.
Both results showed that there was no substantial difference in friction of the road surface between lanes having 100%, 75% or 50% of cars with studded tyres. However, the friction was much poorer in lanes having fewer cars with studded tyres. These results suggest that traffic with 50% of cars having studded tyres results in adequate friction of icy road surfaces in winter. The friction difference between lanes of 50% and 0% studded traffic in the end of the test responds the change in friction levels, when you lower the winter maintenance class by 2 classes in Finland.
On average, the road surface wore the fastest in lanes with high proportions of cars with studded tyres. However, we were unable to accurately measure the increase of ruts due to inconsistent wear of hard snow surfaces.
The report (in Finnish) can be found here.