The load on the trailer is borne entirely by itself, with the locomotive only hooked. The locomotive only provides the power to help the trailer overcome the road frictional resistance. All hanging can rely on their own tires upright. The side of the semi-trailer requires a locomotive to provide a support point, and the locomotive is responsible for providing more than half of the trailer load. That part of the weight of the semi-linked to bear in the tractor, half-hang up to rely on the front of the legs.