18x9 revisited
Tirerack says you can't go wider than 235 which is more appropriate to an 8" rim width. If you want to play it safe, stick with 8" rims on a narrow body.
I've seen SO many different answers on this same question that I will not even attempt to be definitive on this. All I know is that I'm running 235/45R17s on my narrow body A6 and that's as wide as Tirerack recommends. Those tires are sitting on 17x8" wheels. Based on myfitment, I could not imagine getting those that same width on a 9" rim. You could probably get 245s (certainly 255s) but some people report rubbing with that size.
One thing to note: I have the sport suspension. If you do not, your car rides a bit higher and you may have more options. The flip side on this issue is that you may very well want to lower your car if you have not already. An 18" wheel is going to accentuate the large wheel gap non-lowered A6es have.
Good luck. Sorry I can't provide more definitive answers. I'd give the folks at Tirerack a call to see what they'd recommend. Ask for Gary -- knows his way around Audi's better than anybody.



