In this paper, a reference model tracking preview controller is designed for nonlinear tracked vehicle systems. The reference model to be tracked consists of observer-based preview controller and linear tracked vehicle model. The observer based preview controller is an optimal controller at noisy environment such as system and sensor noises. The linear tracked vehicle model is modified to use a rate of vertical road elevation as preview information. Commercial program model is used to verify the control algorithm. The performance of the preview control system is evaluated on the ride quality which is estimated from the acceleration of the driver's position.