Did a search, didn't see it.
Stumbled across this doing research
Vehicle aerodynamics
Fun to play with different car shapes and sizes to see the instant affect on CDA. Also can put a window down, have a flat floor etc. Lets you see the best bang for buck on mods and quantify them.
When added to the
ecomodder tool it gave me a fairly accurate figure for myself and the donkey over the recent run.
Now if I could just find an online CFD program.