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. The underlying criterion is that optimal tractive efficiency provides maximal tractive properties, less fuel consumption, and improved cross-country mobility. Further, by using the developed methodology optimum coordinates for the center of gravity and optimum arrangement of the middle axle wheels along the tractor base are determine.