We develop a comprehensive nonlinear model of a vehicle suspension system which can be used to study control algorithms for active suspension systems. This model is derived using standard kinematics and kinetics and takes into consideration several factors that are neglected in most existing models. Extensive computer simulations were performed using several road profiles and the results show that the proposed model coupled with appropriate control algorithms can result in improved vehicle performance when compared to the commonly used models. The model presented is being used to develop a nonlinear fuzzy-sliding-neural controller.