Brennensthul Marek, PhD.

This article deals with the assessment of traction properties of tyres on forest grounds. The
research was carried out on skid trails located in pine stands. The tested grounds were different
due to the cover of the soil and its mechanical properties. The study also deals with the
evaluation of ways to improve traction by reducing the inflation pressure and using the tyre
chain. The research was carried out using a specialized traction test stand for two tyres (9.5–24
and 400/55–22.5) different in width and tread pattern. The studies showed significant effect
of ground conditions on traction. As a result of changes in the ground conditions, the values
of drawbar force, rolling resistance and tractive efficiency were altered by 25%, 23% and 6%,
respectively. The higher values of the drawbar force and tractive efficiency on all tested trails
were obtained for 400/55–22.5 tyre. Both the use of tyre chains and the reduction of inflation
pressure resulted in the increase in drawbar force and tractive efficiency. A better way to improve
traction properties was the reduction of the tyre inflation pressure, which caused the
increase in drawbar force and tractive efficiency. The use of tyre chains caused an increase in
drawbar force over the entire slip range, while an increase in tractive efficiency has only been
shown for the slip larger than 15%.