went to buy new brake discs the other day and i find out that after putting my reg plate in 3 different sizes came up. 
my car = Audi a6 Avant 2010 2.0TDI 170bhp Lemans spec 
just wondered if there was a way of telling with out taking the disc off and checking 
cheers 

Sometimes you can see it stamped into the outside edge of the disc otherwise its a case of taking the wheel off and measuring it up

 

ok cheers they aint stamped so off they will have to come 

I just did my fronts this week. If you look on the chassis label either in the boot by the spare wheel, or in the handbook you'll see a 3 digit code, 1ZL or 1LG. If it says 1ZL then they are 347mm, if 1LG then 321mm. Hope that helps.

Just brought front set of brembo discs turns out there is a size diffrence the new one's are smaller than the one's fitted how do you know the correct size 

On 5/28/2017 at 8:38 AM, Hoggy1972 said:

I just did my fronts this week. If you look on the chassis label either in the boot by the spare wheel, or in the handbook you'll see a 3 digit code, 1ZL or 1LG. If it says 1ZL then they are 347mm, if 1LG then 321mm. Hope that helps.

Exactly that ! 🙂

there was aslo 360mm for s6 and rs6