The paper describes the most important items in the aerodynamic research related to the development of a racing car. The methodologies of scale model wind tunnel testing and track testing are analyzed. In detail these are applied to the development of the Alfa Romeo 156 ST. The wind tunnel used is described as well as the car instrumentation in the track tests. A comparative analysis is performed between model and full scale aerodynamic results. Finally the influence of the moving belt in the lift measurements of the scale model is considered and the use of the aerodynamic load distribution in the development of the Alfa Romeo 156 ST is described.