Horizontal Forces
In order to set the vehicle in motion, a horizontal force has to be created at the tire tread points of the driven axle. This horizontal force has to be in equilibrium with the acting forces. The horizontal forces acting in the vehicle coordinate system are also shown in the figure. The equations presented in the table show the required horizontal force in the tire tread points at the front or rear axle in FWD and RWD.
The reduced mass moment of inertia θredh(v) at the non-driven wheels only consists of the mass moments of inertia of the wheels and the parts which rotate along with them, such as brake disks. The mass moments of inertia θred of the rotating parts of the remaining drive train are also reduced to the driven wheels and similar to the road resistance force FRh(v) of the driven wheels represents an "internal force" or an "internal moment".
It has however to be considered here that the "internal forces and moments" have to be overcome from the point of view of power by the powertrain. Since the horizontal force in the tire tread points considered here are limited to a definite driving condition, the inner forces and moments need not be taken into consideration.