The Authors have developed a four wheel steering controller which can handl
e nonlinear tire forces. A new technique, Intelligent Sliding Surface Contr
ol, has been used to prevent control system instability induced by saturate
d functions. In this paper, unknown tire-road contact conditions are discus
sed. The robust performance of two types of controllers, a sliding mode con
troller and an adaptive sliding mode controller, is compared using simulati
on.