by Bradford Zoeller
B/Z Motorsports

When you mount a wing on your race car and it moves through the air, the wing will press the car to the track surface giving more grip. But remember that nothing in life is free. By doing this you have also increased the drag coefficient of the car and the engine has to overcome this drag. It doesn't matter if it is a Formula Vee or an Indy car, the engine now has to do more work to push the car through the air. All items including the body has the same effect as a wing. Every little item sticking into the air flow produces drag. How much does that bolt head matter? Let's look at the numbers.
There is a basic equation for the force it takes to push something through air:
Aerodynamic drag = 1/2DAV²
In this equation, D is the density of the air, A is the frontal area, and V is the velocity.
For real body shapes, air at standard conditions, V in mph, and drag in pounds of force, this equation becomes: Drag = 1/391 CdAV²
This equation shows that to calculate drag you need to know three things: Cd the drag coefficient, A the frontal area of what is passing through the air, and the speed of air past it. This equation shows an important point. Aerodynamic forces are proportional to the square of the speed. Said another way - you quadruple the drag when you double the speed.
The drag coefficient, Cd, is important because along with frontal area, it determines the power cost of pushing a shape through air at a certain speed. A car with a small frontal area and a low Cd will have a higher top speed than a boxy car with the same horsepower.
You spend thousands of dollars on your engine to get more horsepower. How much are you wasting? Look at your car and see how many things are sticking out in the airflow.

About the author:
Brad Zoeller has been engineering race cars for over 50 years. His aerodynamic expertise has been applied to victories at the WKA World Championships and SCCA Runoffs. He may be reached at bzoeller@bztec.com