In forestry practice, during forest harvesting there are many different situations while skidding timber assortments, which are dealt with individually depending on the circumstances. The main purpose of this scientific paper is to offer a model for the calculation of the optimal distance for skidding timber assortments uphill or downhill, in mountain conditions. The working area i.e. the harvesting volume is situated between two storey (horizontal) forest roads. This solution would enable the forest experts to make the right decisions when planning timber assortment skidding, i.e. to achieve the most favorable financial results of the work. The method is based on work efficiency i.e. the time required for skidding certain timber assortments (logs and firewood), when skidding is done by animals, adapted tractor equipped with winch, and mobile cable crane.