The aim of the research is to improve the indicators assessment accuracy of the vehicle energy load by improving the method of experimentally - theoretical determination of the aerodynamic drag parameters of vehicle in motion. To achieve this goal, it is necessary to solve the problem of determining the dependence of the energy load level on vehicle speed with varying frontal aerodynamic drag coefficient. Studies carried out to clarify the calculation of the parameters of vehicle aerodynamic drag in motion made it possible to determine the correlation between the actual effective engine capacity and the maximum kinetic energy of vehicle at translational motion. When determining the vehicle aerodynamic drag, the constant coefficient of aerodynamic drag is used depending on the speed in all range of vehicle speeds. This leads to significant mistakes in determining the necessary engine capacity expendable to overcome the aerodynamic drag, and vehicle fuel consumption. As a result of the research, analytical expressions, allowing to take into account additional energy losses and correlation between the kinetic energy of the vehicle steady motion and the effective engine capacity have been obtained. The theoretical contribution of the research is that the correlation coefficient between the kinetic energy of vehicle in motion and the effective engine capacity – have been proposed. Studies have shown that if speed of vehicle increases the indicator will monotonously decrease in the range of actual speeds.