The expansion of wheeled mobile robot usage to applications with high loads and speeds requires reliable tracking control that is robust to the disturbances emanating from external loads and the wheel-ground contact. The motion of such robots can be accurately described with a dynamic model that includes both the external forces and a complex tire model. However, control design from the full dynamic model is not practical due to its complexity and non-analytic form. In this paper, we derive a simplified dynamic model which is adequate for control design and treat the remaining terms as model uncertainty. Then, the uncertainty is analyzed and a robust control algorithm is designed. The performance and robustness is proven through computer simulation.