[RedDevil]

Originally Posted by aerohead

The premise of the simple canoe fairings,is that the front airdam is shearing most of the air away from the underside,and the flow which remains is traveling for the most part,longitudinally towards the rear.
*The smooth underside is a 'wall' with the wheels erupting out of it,contributing interference drag from these Cd 0.488 rotating wheels with 'MOONs' on both sides.
*The 'wall' affects the boundary layer thickness around the fairings,and by the time the horseshoe annulus at max. cross section displaces to the tail of the fairing,the semi-circular cross section of the boundary layer is quite thick geometrically by comparison,significantly altering the effect of the fairings performance.
*Hoerner reported that due to this interaction,it was beneficial to lengthen not only the aft-body of the fairing,but also the forebody,with minimum drag occuring for fineness ratios between Length/Height = 10 and 15.
*A marginal fillet at the fairing/wall intersection also was found to be efficacious in reducing drag (as you see on all aircraft wing roots) ...

I see. I might have been too obsessed with my own car.
On this car, with the air dam and flat bottom, I agree the fairings need to follow the air flow under the car - which is, be straight.

I like to think that the toe-in front wheel fairings may serve as an aid to or even replacing the front air dam when it is not possible to make that low, forcing the air aside; keeping them short (merging upwards into the body) for practical rather than aerodynamical purposes.
As you pointed out this should be put in another thread though.