Nacrtak The motion resistance ratio, gross traction ratio and net traction ratio of a wheel cable skidder were determined and mathematical models derived for three tire inflation pressure values with or without tire chains on forest road in mountainous conditions. The motion resistance ratio increases with the increase of tire inflation pressure. On the contrary, the gross traction ratio increases with the decrease of tire inflation pressure. However, when the tires are equipped with tire

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... the skidder motion resistance is higher. The motion resistance ratio with tire chains also increases with the decrease of tire inflation pressure due to windage between the tires and chains, which results in lower tractive performance of tire chains. Therefore, by using tire chains, an increase of gross tractive ratio could be achieved, as well as the increase of motion resistance ratio compared to tires without chains. The results of the study show that it is strongly recommended to use tire chains as tightly as possible.