Quite a few decades (!) ago Keith Plestead (Mr. PB Racing) did a test with a rear wing shaped like an aerofoil to create more downforce at the rear. It didn't work! The car was very loose at the rear and difficult to drive.
Keith concluded that all the rear 'wing' on a model car is doing is creating drag behind the centre of pressure to stabilise the car. As the Veyron and McLaren F1 have a wing that pops up under braking to do exactly that, it seems like a logical conclusion.
Dimples also feature on TdF cyclists suits to reduce drag, so there must be something in it. It seems reasonable to assume that the areas of surfaces we have are too small and the speeds we go at too low for any of these things to have a noticeable effect.
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