Vehicle dynamics are dependent on tire/road contact forces and torques, which are themselves dependent on wheels and vehicle loads. These loads induce normal forces which are very important to calculate road and bridge damage or to assess the LTR (Load Transfer Ratio) used to prevent or forecast rollover of the vehicles. A good evaluation of these loads and normal forces requires an accurate description or modelling of the road profile, which is an input to the heavy vehicle dynamic model. In this paper, we study the influence of the road profile elevation on the wheel and vehicle loads. Several road profiles are measured and applied as an input to the heavy dynamic model developed in LCPC ([7]). Then the corresponding wheel loads are evaluated on each wheel. The estimation is done using sliding mode observers. Simulation results from the PROSPER simulator are presented on the estimation of vertical forces, and discussed to evaluate the robustness of our approach and to assess the impact of the road profile.