[onewhippedpuppy]

Originally Posted by RWebb

ground vehicles are not so "easy" - still have to deal with the highly vorticed flow aft of the wheels

would we want some downforce at speed?

and what about the undertray?

All true, I was just answering the "ultimate aero shape" portion. All of the theoretical stuff breaks down when you have to provide practical considerations. Maintaining the shape would be ideal, and the challenge. Fender skirts vs open arches, symmetrical body top and bottom, flush mounted and gasketed seams, narrow and low rolling resistance tires, all would help. You could use an aero device to create downforce at speed, basically a spoiler that slowly deploys to give the airflow shape some camber. It would be a challenge to keep the airfoil shape and still make a usable interior as well.