You've got the formula wrong (a little). It's drag_co * surface area * velocity
^2
All cars have a drag coefficient. It's the ability for air to pass around the vehicle. The only way to find this number is to have the car tested in a wind tunnel. Here is a video of this being tested:
Then you derive the force of the drag (f_drag) from the amount of area pushing against the air, by the drag_co, and by the speed at which it is hitting the air.
If you've got a better formula for figuring this out, please let me know, because this is the way I was taught how to find the force of drag. As far as I understand, the only drag quadratic equation is for fluid. Am I wrong? Here is the formula I've broken down, maybe I missed a step, but this looks right to me:
Drag equation - Wikipedia, the free encyclopedia