The invention relates to a method and system for determining an aerodynamic drag area CxA of a moving vehicle, for example a bicycle, in dependence upon the airflow yaw direction and speed without the use of a wind tunnel. The vehicle is equipped with sensors for collecting time-stamped values indicative of the vehicle speed, propulsion force, airflow speed and yaw angle of the airflow at various points during the trip. The trip data are then processed using successively refined hypotheses regarding the CxA(yaw) dependence to generate a plurality of elevation profiles for the travelled path. The generated elevation profiles are then evaluated based on available route elevation information to select a correct dependence of the aerodynamic drag area upon the yaw angle of the airflow.