OK, just to confuse things further, here's something I ran across late today. It's from an SAE paper, 951906, "Vehicle Design Strategies to Meet and Exceed PNGV Goals" by Timothy C. Moore and Amory B. Lovins, found here
https://www.rmi.org/images/PDFs/Tran...nStategies.pdf
The following comes from page 11:
"Rather than smooth the underbody and attempt to tuck chassis
components up out of the flow, the industry strategy has
tended towards air dams below the front bumper to force much
of the flow around the vehicle rather than under. This needlessly
increases frontal area and leads to the erroneous notion
that achieving very low aerodynamic drag requires extremely
low ground clearance[5]."
Footnote [5] says:
"If chassis components are streamlined or otherwise covered
by a smooth floorpan to prevent interference drag, there is
little reason, beyond the limited exposure of more of the tires’
frontal area, to prevent the airflow from passing under the car
(P. MacCready, AeroVironment, personal communication,
April 1995). Allowing the airflow to pass under the car can
actually aid in eliminating lift-induced drag."
In case you are not familiar with "P. MacCready" or AeroVironment, see
http://en.wikipedia.org/wiki/Paul_MacCready
If you look at the Viking cars by Dr. Seal, mentioned by aerohead above, you can see that he took pains to deflect air from in front of the wheels, but did so without front air dams or lowering ride height. The entire collection of cars can be seen from here (click on the boxes to see photos):
http://vri.etec.wwu.edu/cars.htm
Sadly, I have not found anything in the way of technical descriptions of these cars beyond the one paper here:
http://vri.etec.wwu.edu/hybrid_paper.htm
About 3/4 of the way down the page is a nice paragraph on aerodynamic drag reduction which does not include lowering ride height as one of their strategies.
Now, you will notice that nothing I've quoted here says that lowering ride height *won't* decrease drag--it just says you don't need to lower the ride height to achieve low drag.
--Steve