Several studies have been conducted in an effort to bring Computational Fluid Dynamics (CFD) out of the research arena (5) and into the product design environment as a useful aerodynamic design tool. The focus of these studies has ranged from extremely simple shapes to more complex geometries representative of real vehicles. This paper presents the results of real vehicle applications in which CFD was used to predict the aerodynamic effect of proposed surface modifications. The simulation data was generated using a numerical method derived from lattice gas theory to evaluate the aerodynamic effect of surface modifications. The commercial software Powerflow was used to prepare the model, perform the simulation and post-process the results. These case studies were performed in parallel with real vehicle development programs. The depth of experimental comparison data was limited by traditional vehicle program timing and budget constraints. Comparisons were made between the predictions and the experimental data to determine the relative accuracy and usefulness of CFD in predicting the aerodynamic effects of surface changes. Flow visualization comparisons were a major metric in evaluating the accuracy of the simulation. The feasibility, merits and limitations of using CFD in the vehicle aerodynamic design process are discussed.