[MetroMPG]

Ah! Neat.

Comments: I have read that it generally does not pay to increase frontal area just in order to achieve the ideal shape. (Although I read that in the context of roof design.)

I mention that because it looks like the leading edge of the skirt would have more of a gap between it and the tire/wheel than the trailing edge. Just minimizing the gap, and keeping transitions as smooth as possible with that constraint, might be the best approach.