4.3 Tractive force
Tractive force is the force needed to overcome the resistance caused by friction when two bodies slide or roll on each other. Compared to the resistance generated by friction, tractive force has the same intensity and the same sense, but the opposite direction. The lower the force needed to keep a equipment moving, the greater the smoothness of the wheel applied to the moving equipment. In the specific case of a wheel rolling on a flat surface, the tractive force must overcome the resistance caused by rolling friction - that arises when the wheel comes in contact with the surface - and by sliding friction - generated by the mechanical bore and axle set coupling.