Online Aero Calculator
 

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.

Good find! Looks fun to play around with.
This is somewhat useful to!
Automobile drag coefficient - Wikipedia, the free encyclopedia

ripped-off from MIRA
 

They've plagiarized 'A Method of Estimating Drag Coefficients,' by,R.G.S.White's research paper from MIRA,1969.
Shame on them!

Reply to Xntrx
 

I made all my aero mods on the red VX from ideas found here on Ecomodder and I did no math calculations. Because "maths" hurts my brain.

I am convinced that if you added some more aero from ideas on this site, you will see great results in your MPG.

I have picked up at least 10 MPG from what I did and I know some of it is "Down and Dirty" but still worked to some extent.

Also, any aero benefit you can add will always be helping MPG from now on, no matter how hard you may or may not be trying to hypermile.;)

...and THAT, folks, is *why* nomographs were developed -- no math -- just cross the lines and/or pick the appropriate outlines!