[ERTW]

You forgot "induced drag", which is caused by lift on a body. Trying to direct all the air on the trailing edge near the ground creates lift...especially if you don't have a 20 foot tail.

struts are at least 20x wider than their chords. End effects don't matter. Car bodies are relatively narrow, and the above rules of thumb do not apply.

wind drag *begins* to have a greater effect than friction at 50 mph. more streamlined the vehicle, the higher that speed. there is a point diminishing returns, where fuel economy doesn't increase, and the manufacturability, and style, go out the window.

GM seems to design its cars to a CdA of 7.0. Germans are a little better, at ~6.0. Engines are designed to operate with a load, and 2500-3500 rpm. A super low drag car, cruising at 1500 rpm, is not optimum. imo the aero civic owes more to its lean burn engine (wouldn't pass emissions in certain areas) than to its hideous boat tail.

Can OEM lower CdA to 5.0-6.0 without increasing cost? Yes. will it improve hwy mileage at 60 mph? not much, if at all. If the government, like aerohead wants, raises speed limits to 100 mph, then yes.