# Are there any methods to figure out how aerodynamic a race car is without a Cd number?

For the top speed of a car, I believe it's usually limited by drag and horsepower. However, I've also learned that gearing can affect the top speed and acceleration of a car. Are there any methods to figuring out how much more aerodynamic one car is to another only using speed and power? I know this sounds unclear so I'll provide an example: The 2009 Corvette C6.R has 590 hp and can reach 200 mph. The 2008 Aston Martin DBR9 has 600 hp and can reach 180 mph. If you give the C6.R 600 hp, its new theoretical top speed would be 201.1 mph. Does mean that it is more aerodynamic, or is there more to it?

• There is more to it. Sep 16, 2021 at 12:07
• I can guarantee that gear ratios and final drive are causing the 20mph difference in these two cars, not aerodynamic drag. Sep 16, 2021 at 17:22
• I believe it's usually limited by drag, weight and horsepower. Sep 16, 2021 at 21:15
• @chili555 On a flat surface, weight has little to do with top speed. Sep 20, 2021 at 16:33