[aerohead]

Originally Posted by Vman455

This is a "rule of thumb" that appears to have sprung up ex nihilo here, since it has no basis in any literature that I've seen (and I've read a lot of references).

The good news is, you can easily test to see if an air dam is reducing drag, and what height might be optimum.

There's been a bit published about airdams since 1960, when Chevrolet Division of General Motors introduced it to the motoring public.