[Smokeduv]

I think they look awful when they are just a hole cut in the bumper, and as many of you, I think that they don't really work, but I have doubts. As I'm in no way an expert in aerodynamics, I see two trends here, one is having the rear bumper as low as possible and with a complete undertray to have the lowest drag, which seems correct as there is data to support it, and the other is having some kind of rear diffuser to lower air speed and fill the low pressure area behind the car, which can have many advantages but needs major understanding. I think that these holes could be in this last trend, but they are awful and don't have an specific study for every car (if for any).

I can recall an interesting example (at least for me), which is the 2010 F1 season where the winner car was the Brawn GP, which was controversial for having a "double-decker" rear diffuser, so it could have more area (the rules for 2010 shortened the diffuser length, so having a way to increase area within the limits was key) and with no major impact on drag. Can these two-layer thing be applied to a car who has a low bumper, but can fill the wake also?

Another thing I can remember is that the wheels makes big turbulence in the wheel arches, so they make holes to lower drag (see LeMans Cars with a big opening at the top or many sports cars with an opening behind the arches), so, for the rear wheels, a way to manage this air to the back could be beneficial. I don't know, maybe I'm just saying incoherent things, but is what I have seen (as in the examples) and with my very limited understanding about aerodynamics.