Tire size vs wheel size
 

I found a beautiful matched set of 18" Audi wheels although from an A8 and I've got the same year A6 with OEM 18", Audi parts cross checked my VIN with the new wheel numbers and they'll fit but I forgot to ask if they'll take my OEM tire size..duh, mine are according to the book 245/40/18 tires whereas the A8 took 255/45/18? Will I need to order the 255/45/18 tires to fit these wheels and will this change things such as true speed readings or can I put my OEM sized tires on?

Are you sure they'll fit in there? Do you have a 4.2L. My A8 has some wide tires on it I can't see them fitting my A6 at all. But my A6 is a 3.0 so I don't have wide wheel wells.

I'm sure only if the research the Audi people did cross checking my VIN with the new wheel serial numbers before I purchased them was correct and I made sure they knew the wheels came from a A8 which the wheel serials numbers showed, my A6 came with OEM 18" wheels with Adaptive Air suspension (A8 feature) so it's not the usual fare. The difference I found was the actual tire size between the two cars which seems fairly slight and your question will definitely need to be answered in my mind before I order tires, needless to say I am alittle more then concerned but still trusting the Audi research. I'd feel better if my OEM tire size will fit these wheels. BTW..I have the 3.2 engine.

Are you asking if you need A8 tire sizes? The answer would be 'no'. Use the one recomended for your A6 - 245/40/18, or any combination that keeps the diameter w/in 1% to be safe.

Put your std 245-40-18 tires on the wheels -Your car will not know the difference in wheels as long as the offset and wheel width is the same.

I was hoping I could stay with the same sized tire, thanks all

the large stretched size of tire is best as it catches the road even when the car is moving at high speed.