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The M-B Bionic concept illustrates that a blunt front is okay, but a low drag car needs to have a very small rear. That explains a large part of the difference between the Cd=0.095 clay model and the Cd=0.20 concept car, which had a relatively large rear. The rest may be due to adding door handles, wipers, ground clearance, and panel gaps. CarBEN's rear is much larger than that of the clay model. As a percentage of frontal area, it's somewhere between that of the Cd=0.25 Insight and the Cd=0.188 EV1.
Traditionally, tall vehicles need a wide track for stability. However, going electric and mounting >1000lb of batteries below the floor gives you the option of being tall but not wide. See the Commuter Cars Tango for an example of this.
If you can find a way to make your car a foot or two narrower while staying within your project's goals, you'll end up with a much lower Cd, and a much much lower CdA. Such a car should be called the Trout, instead of the Boxfish. A conventional streamlined car has very long overall length to taper its roof down to meet its floorpan. Instead, the Trout is very narrow to achieve a similar Cd with a shorter overall length by having its sides taper inward until they meet. The Trout does well in a wind tunnel, but less well in a crosswind.
Thanks for the thought-provoking thread.
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