<div class="htmlview paragraph">From the standpoint of safety, the demands are growing in recent years for better controllability and stability of automobiles and in particular in trucks. The truck, however, when compared with the passenger car, is subject to larger changes in gross vehicle mass and center of gravity depending on its load placement. In addition, since the cornering power generated by the truck tire per load is smaller than that generated by the passenger car tire, it is difficult to introduce significant improvements in controllability and stability simply by use of passive techniques like suspension characteristic tuning.</div> <div class="htmlview paragraph">Therefore, studies were performed on the applicability of the 4WS system, an active vehicle dynamic characteristic control technique, to a Truck as a means for solving these problems.</div> <div class="htmlview paragraph">This paper present an overview of the medium duty truck version 4WS system, explains the effects of the system for improving controllability and stability on the basis of analytical simulation and full vehicle tests, and concludes that the 4WS greatly contributes to improving the safety of the truck.</div>