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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.

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.

Mass and geometric parameters of all-wheel drive off road vehicles, such as coordinates of the center of gravity and arrangement of the wheels, have been obtained to satisfy cross-country mobility profiles that reduce the dynamic normal loads on the running gear system. However, the influence of these parameters on tractive properties for basic cross-country mobility of vehicles receives less attention. The authors have developed a new method for determining mass and geometric parameters that provides optimal tractive properties for basic cross-country mobility of off-road vehicles. The methodology is realized using a mathematical model of a 6WD tractor on a deformable road surface. The mass and geometric parameters are achieved by optimizing the tractive efficiency function to provide the best transport efficiency on all running gears.