The recent facelift of the Chinese version of the VW Bora incorporated several changes of the styling of the upper body. In particular, front facia, A-Pillar and rear end were subject to design changes. As major effects on the aerodynamics performance were not expected, extensive wind tunnel testing for the upper body design changes was not included in the development plan except for final performance evaluation. Nevertheless, an aerodynamic study of the effects of the design changes was undertaken using a CFD based process. At the same time, the facelift offered the opportunity for reducing the aerodynamic drag by improving the underbody flow. The design of the engine undercover and the wheel spoilers were considered in this effort. For this purpose the CFD based aerodynamic study was extended to include respective design features. The whole study was carried out using a response surface method as a mathematical model to characterize and understand the effects of the design changes and their interactions. This approach allowed achieving best possible insight at a minimal effort. In addition, possible optima for the underbody optimization were identified. This helped to determine a possible trade-offs between cost and performance and also allowed a reduced effort in the wind tunnel for fine tuning the underbody design changes.