The two dominant motions of automatic vehicle steering control are yaw and lateral motion. A two degree-of-freedom(DOF) model commonly used to describe these motions is called the bicycle model. Experimental results for certain vehicles, however, show the lowered gain characteristics in the lateral acceleration response to the steering input. This is attributed to suspension dynamics. In this paper, a 3 DOF linear model, which incorporate the suspension roll mode, is developed and verified against the experimental data. The H ∞ theory is applied to the bicycle model and the 3 DOF model for synthesis of robust steering controllers. The simulation results indicate the importance of the effect of roll dynamics to steering controller design.