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According to the tractor theory, the operating mass of a tractor is calculated from its traction force required to overcome the resistance of soil-cultivating implements and provisional incidental overloads. Implements' resistance changes are estimated by the coefficient of possible overload -- the ratio of maximum possible resistance to its average value, i. e. the maximum resistance value of the implement is used for calculations One of the regulating agricultural operations in the choice of tractor's operating mass is plowing. Besides, the implement's resistance change with the speed increase of the tractor's aggregate is not taken into account. The operating tractor's mass calculated by this method is by 10…20% different from the optimum operating mass.

The investigation is concerned with dependencies between a friction coefficient of the tire with a road, μ, and wheel slip, s. The analysis of μ-s-dependencies is given in the paper. The conventional approach to their presentation contains some discordance with real physical processes. On the basis of the external friction theory it is possible to offer another concept of potential μ-s-curves. The potential μ-s-curve is a function of the deformative, adhesion and transverse components of tire grip, the absolute slip velocity and the road reaction. Over the interrelation character of the given components it is possible to evaluate a current road-operational situation. In addition the recommendations for practical use of the potential μ-s-dependencies for the Systems of Active Safety are given.

To develop better performing vehicles, for ground transportation, it is necessary to improve the theory in vehicle dynamics for choosing suitable mass and geometric parameters for highway as well as for off road trucks. A new approach is required for choosing such optimal mass and geometric parameters. The present paper is devoted to this problem. A new method for synthesis of mass and geometric parameters is introduced here. The method allows us to synthesize the parameters in such way as to provide a vehicle with the best transport efficiency under various road surface conditions. Constraints such as limitations on these parameters, vehicle running modes, mass and geometric parameters are included in the model. Furthermore other constraints for vehicle running abilities which are dependent on mass and geometric parameters, as well as an algorithm for synthesizing mass and geometric parameters are also included in the paper for pre-optimization process.