What is the widest 18" rim front and rear allowed on '06 A4?

I went 8.5 on my 99.5 A4 Quattro

How much clearance did you have left? I have some 10" wide wheels for the rear and 8" for the front.

Well they should be ok depends on what offset I have 35mm

I Have 19's by 8.5's on the back of my B7 A4 and its been lowered... when i have a full car they rub!!! i would like to see 10's

Flyinb501 has 19x9.5 in the rear don't know if he fixed his rubbing problem or not

Yep. I just found a wheel shop by my house that can increase the offset. I'm gonna go to a +35 offset from my +32, and that should clear up all rubbing issues. There are a ton of b6 guys running 9.5" in the rear, and I know of one guy that has 10" wide in the rear. I think the b7 has about the same amount of room so you may be able to pull it off depending on offset.