Quote:
Originally Posted by Diesel_Dave
There's some value in both Cd and Cd*A. Cd*A is what does ultimately determine the aerodynamic drag force, however, Cd allows comparison of different sized vehicles. For example, it makes no sense whatsoever to compare the Cd*A of a tractor-trailer to that of a small passenger car, however, comparing Cd is a fair comparison.
It also makes sense for scale testing in wind tunnels. Cd stays the same for the scale model and the full-sized version, Cd*A obviously changes (because of A).
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what you wrote makes no sense to me.
I don't compare fish to birds. I don't compare tractor trailers to hatchbacks.
Comparing Cd is worthless between the two.
Cda is what matters, because if you combine speed, Cda, and weight, you can KNOW the drag of the car.
Cd is a way to sort of calculate Cda, but it is kind of worthless by itself.