Similar to the traditional method of aeronautical wind tunnel testing a procedure to correct for support interference and wind tunnel interference in the automotive wind tunnel of Jilin University is described.Due to the fact that a moving belt is installed in the centre region of the test section the model was kept in place by an external support system. However, for our tests the moving belt was stationary. In order to separate the different interference effects two tests were carried out with the car model connected and disconnected from the support-structure linked to a six-component underfloor balance. In this way the aerodynamic force on a car model, which is then still contaminated by wind tunnel interference effects and the secondary interference effects of the model support on to the car model can be determined. The latter effect is further determined with aid of computational fluid dynamics by comparing the results of the vehicle in an equivalent numerical stream with the support structure present but disconnected from the chassis of the car and with the support structure removed. Finally, the wind tunnel interference effects are determined by a test section correction procedure.