What does this wheel arch plate do?
 

There are small (5.5”x 1”) plates installed on the back of the wheel arch. What function do they perform?
https://cimg4.ibsrv.net/gimg/www.aud...5ac94df31.jpeg

So that the tire doesn't stick past the fender.

Can't recall, but I think it's the result of some sort of legal requirement in the US discussed here before.

It’s on all cars/suvs?

Exactly....tire not allowed to stick out past fender and offers some body protection there from debris.
It can be easily noticed on MKI SQ5 with 21" wheels vs a standard Q5.
What is even more interesting and probably lesser known is on the C7 if you decide to go aftermarket 19"+ you need to install a guard over the fuel filler pipe. Basically for the same reason as the wheel arch guard.... protect those areas from larger wheels.
"Vehicles with factory-fitted wheels up to 18" require the additional installation of a protective cover on the fuel filler pipe. The protective cover is already fitted to vehicles with factory fitted wheels of 19" or larger.| Protective cover part number: 4G0201974"
I'm betting there is more than one C7 that moved from 18" wheels to 20" without installing the guard.

It is flush with the fender and is only 5” long. How much protection could it offer?

Yea how does this prevent the tire from sticking out past the fender?

Just enough.

It protects the fender edge because the large size tire sticks out and kicks up rock along that edge. Take it off and see how long before the paint is worn away there. Also there is surely legal requirements by the manufacturer to not have the tire stick out past the fender by some certain amount in specific locations (who knows the exact specs?), so they put this small guard there. simple.

Here you can see it on a MKI SQ5 circa 2014.
http://www.prestigewheelcentre.co.uk...3-1024x768.jpg

It’s a law that the tire cannot extend past the fender. If it does it fails Nys inspection.

The protection this strip offers is laughable, its just there to meet a technicality. Audi cares little about protecting the car or people behind you or they would flare the fender. They just want to pass the law by the skin of their teeth for the cheapest way possible. Not the best way possible. Never saw that on any other major brand.

When I ordered big wheels on my Jeep they insisted i install big fender flares or the dealer would not sell / install the wheels and tires for me in Ny. Come on Audi do the right thing. The more you know.

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