Interesting writeup on the basics, good diagrams
 

I thought this was really helpful to get a visual on whats happening with airflow.

Race Car Design Tips and Information - Aerodynamics

~SM

It is an interesting website.

It was laid out in 1999 using tables. The software section doesn't seem to give version numbers; those change frequently. The pages were last updated on 20130306.

Still, there's probably something of value in there.