I just "discovered" this earlier thread on the subject of Chevy potentially fudging Cd numbers. I wish I had found it before I let loose on Phil. Much of what I tried to discuss has been pretty thoroughly covered by others. Sorry Phil.
http://ecomodder.com/forum/showthrea...0-a-11313.html
Now that the Volt number have been adequately cast into doubt, I want to make a small case on the EV1. From the one Cd ref I found, it appears that they claimed .21 for the car. I saw one of the cars at the Green Drive Expo in Madison a month ago. (As I understand it, someone managed to retain this one, less drive train.) I have to say that again I don't trust GM's numbers. I try to relate what I see on the EV1 to the Insight 1. I see considerable similarity as far as Cd development goes. They both have mirrors, and closed rear wheels. Their front wheel openings are well rounded, with perhaps a small advantage to the Insight. They both use aero wheels. They have rather similar stagnation points at the front.
Certainly the EV1 benefits by having no front radiator opening, but this benefit, according to Hucho, is only about .02 over the Insight 1 setup. (See Hucho. edition 4, figure 4.97)
The EV1 is handicapped by being too fast at the rear, while the Insight 1 is pretty darn ideal, IMO.
Bottom line is that I don't think GM can justify the .21 for the EV1, not that it really matters is a practical sense. It only matters to those who are interested in theory and modding.