How does this work? (possible aero content)

[BOBTEE]

I parked next to a Citroen C4 the other day and whilst waiting for the GF noticed how the dirt gathers around the quarter panel/bumper join.



Is the dirt going forward or just gathering at the end of the quarter panel? Why is the bumper clean?

A bit closer

[P I Staker]

My Mums MK5 Golf 5 door does just this around the rear shut line of the rear doors. I have wondered about it before my self.

[alistair1234]

White rep-mobiles are really bad for this.

[Mave]

Dirt coming forward (anticlockwise) off the wheel?

[Mercury00]

I'd guess air is being pulled through the gap. I imagine if you were driving in reverse all the time the bumper would be dirty instead.

[FourWheelDrift]

Is there a anywhere in the wheel arch where water spray thrown up by the rear tyre could work it's way out?

[BOBTEE]

I wondered if there was a pressure build up in the arch forcing stuff through the gap but why isn't it going down the bumper? I'm starting to think it's dirt shuffling down the quarter but again why doesn't it go down the bumper?

[Eighteeteewhy]

[wolfracesonic]

Eighteeteewhy said:

Does this show where the flames come out on 991 gt3?