Hey.

The wheels that i fit on my A4 are the A6 C7 wheels. If i remember correctly (i don't have the car anymore, changed it with a Q2 for my wife) the specs were 8.5 x 20, et 43, tires 255/35/R20 (you may use 255/30/R20 if the quality of the roads allow it).

The only thing that you need to do to "accommodate" the wheels with 255/35/20 tires is to make a bit of space for the rear ones by tying with a plastic wrap the plastic wheels arch, otherwise it will rub slightly.

Hope it helps! Good luck!