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The stability of a forest vehicle apart from the longitudinal and transversal stability angle implies the safety of tractor anchoring during timber winching. Timber winching is a dragging of timber assortmens on the ground from the stump to a forest vehicle equipped with the forest winch. At a certain limiting load and slope of the terrain, disturbance of the longitudinal stability of the forest vehicle with the winch is occured. In this case, the adhesion factor of skidder and tractor on the ground is an important indicator of the possibility of safe and proper timber winching.
The adhesion factor of the skidder during timber winching on the slope is detremined on the basis of the general expression of the adhesion factor on the skidder on the flat ground. Also, determined the dynamic model of the loading of the forest vehicle is presented during timber winching on the slope.
The results show the horizontal components of forces in the rope and the limiting masses of the loads during timber winching by skidder Ecotrac 120 V. According to the obtained values of the horizontal components of forces in the rope, it can be concluded that the stability of the vehicle, defined by the displacement of the vehicle backwards is the limitation of the timber winching.
The presented model of timber winching on the slope shows the basic principle for determining the limiting load masses and slope of the terrain, which can applied to all types of forest vehicles equipped with winch as well as easily be adapted to other conditions of timber winching at different positions of the vehicle and the direction of timber winching.
Key words: timber winching, tractor stability, dynamic model, limiting forces, load masses