that_tg

2013 US spec A8L 4.0t

Looked everywhere. How do I find out the Diameter of the front and rear discs?

Yes, I know I should measure them but that would be taking the wheels off to make sure it is accurate. I will do that if need be.

Thank you.

NotoriousGLU

Go on europaparts.com and start chat give them Vin number and they will tell you what rotors size you have.

dwboston

Or call the local Audi dealer's parts counter with the VIN and ask them. That's what I did for my A8.

MP4.2+6.0

A guess is the 380mm ones, but here has always been confusion about this. Choices are 356mm, 380mm and 400mm IIRC. 400mm goes with S8 and probably W12. Apparently only with S7 among the others with essentially the same motor as A8 4.0T. Also, if you don't have the big honkin' chunky Brembo style and look calipers, you don't have 400mm. 356mm to 380mm is a full inch apart. You should be able just to guesstimate that with a tape measure with wheel on, looking through to rotor.

Also, I think 380mm (and at least the 400mm) are dealer only. Thus you will end up there anyway if 380mm, so just have some place like audiusaparts.com confirm by VIN as others are saying. Discounted dealer price for the rotors is not bad actually, especially considering they are effectively two piece that are usually pretty big bucks. I think the 356mm ones--the 3.0T size?--may be out there at times from other sources seemingly tied to Zimmerman. There is apparently a patent on the quasi two piece set up, and hence why sourcing is generally just via dealers.

dwboston

The 380mm ones were correct for my 2015 NWB A8 4.0T.

that_tg

After calling the dealer in Minneapolis it does look like I have 380mm in front and 356 on the rear.
The dealer was sort of a dick about it but did finally confirm this.

Thanks to all!