I have a 21 reg 50tdi Vorsprong Allroad. This model is probably the heaviest A6 Avant at roughly 2200 kg. It comes with 21-inch wheels as standard on a 245/40 section tire on a rim of 8.5 J. Originally fitted with a continental sport 6 silent tires which were okay, but they don't last even with normal motorway driving. I'm approaching 12,000 miles and they will be due for a change soon, 90+ % has been at just above regular motorway speed on the M4 M5 or A3O3, nothing too stressful for the tire. When I bought the car last March I was surprised it didn't have 255 section tires, 245 is probably a choice for economy and road noise I suspect to keep the consumption as high as possible. The problem is for me now is there is very little in that tire size available, not just in production but actually available to buy now. They're not the cheapest tire either, there appears to be more 255/35/ 21 section tire choice and I know the rim will take them technically but I'm not sure if they are recommended? I think this is the same issue for the S6 although it does have a different offset. The car has four wheel steering which may be a consideration. If you look at some of the American and even European forums they seem to put massive wheels on the cars but usually previous generations. The C8 Allroad has an ET37 offset the S6 is ET43 on the same size rim. Thoughts, please? PS I have spoken to Audi and they were no help as they only do up to 20 inch tires I was told.