Just off the top of my head (gotta let some of that hot air out) might reduce the vortices usually formed at the top rear of the front tires, and possibly the jetting vortices formed at the front of the contact patch.
http://www.cfd.hu/pdf/10%20Dr.Regert...2010.11.11.pdf
Sorry to repeat myself. I posted that link on another thread. But here's another one which is pretty damned interesting in its own right. look at fig.9
http://www.cadfamily.com/download/CA...ber-Opel-f.pdf