Effect of open windows on car drag and consequently on the required power and fuel consumption has been investigated in this study. To do this, a simulated model as possible as similar to the actual model has been considered. For example round angles and side slopes have been considered. The drag caused by aerodynamic forces has been calculated, for different cases. Results show, as the percentage of windows opening increased, the car drag first decreased and then increased such that, the car drag with open windows for a certain percentage is equal to that of the closed windows car. This certain percentage depends on the car velocity.
