Here's a couple shots of the SolarWorld GT car,Cd 0.14 wheel spats.
You can see that they affect not only the tire face,but also the wheelhouse which can't b controlled by the belly pan.
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On HONDA's Dream 2 solar racer,they designed the front wheel pans to move with the suspension along with Lazy-Susans which rotated with the front wheels,effectively sealing off air to the tire within a fraction of an inch.They were able to achieve Cd 0.10 with this design.Steering was set up like that used on outboard boat motors.Very clever!