A distinctive feature of unmanned and conventional terrain vehicles with four or more driving wheels consists of the fact that energy/fuel efficiency and mobility depend markedly not only on the total power applied to all the driving wheels, but also on the distribution of the total power among the wheels. As shown, under given terrain conditions, the same vehicle with a constant total power at all the driving wheels, but with different power distributions among the driving wheels, will demonstrate different fuel consumption, mobility and traction; the vehicle will accelerate differently and turn at different turn radii. This paper explains the nature of mechanical wheel power losses which depend on the power distribution among all the driving wheels and provides mathematical models for evaluating vehicle fuel economy and mobility. The paper also describes in detail analytical technology and computational results of the optimization of wheel power distributions among the driving wheels. The presented math models of a multi-body vehicle with any given number of the driving wheels and type of suspension are built on a novel inverse vehicle dynamics approach and include probabilistic terrain characteristics of rolling resistance and friction, micro- and macro-profiles of surfaces of motion. Computational results illustrate up to 15%-increase in energy efficiency of an 8x8 vehicle that is guaranteed by the optimal power distribution among the driving wheels. This technology can be applied for improving energy/fuel efficiency and mobility of tactical and combat military and unmanned robotic vehicles with mechanical and mechatronic driveline systems, vehicles with individually-driven wheels and vehicles with hybrid driveline systems.