[lunarhighway]

sorry perhaps i should have explained things a bit better, the big black opject represents the left front tire, seen from above and the curved limes represent dams intended to divert air away from the tire and the wheelwell behind it.

these dams are quite common on almost every curent vehicle.
some are straight and only cover the tire or the suspention on some cars i've obseved these dams curve inwards near the center... mostely bmw's audis, and the new ford mondeo have this layout. the ford seems to have two separate dams however separated by a gap of about a cm.

what i did was extend the weel whell liners in from of the tires with a strip cut from a cheap plastic bucket, handy as this already has a curve in it.

i had planned to use the leftover bits of the bucket to make small curved dams in front of these dams but when simulating this they didn't seem to produce something that was vastly different from the first movie.

but when i added the gap this changed the behavior drasticly as you can see in the movies.

based on this simulation one might conclude a gap between the portion in front of the tire and the curved portion would be a good idea.

my theory is that he full dam acts as a single vortex generator while the split dam might act as two vortex generators produceing counter rotating vortices.