18x9 with 255/35-18 tires,offset +44 or +45. These pictures are with stock 225/40-18 tires,but I have tried the 255s and they work. The 255s have identical revolutions-per-mile as the 225s,so ride height and effective gearing are unaffected.

 

I know this post is a little old, but I have a 2009 Audi A3 8P which currently has 7.5x17 ET56 Wheels and 225/45R17 tires. I was looking to use 8x17 ET47 wheels off an A4 with 245/45R17 tires. Based on our post it seems like that should work, but when I feel behind the wheel, it really feels tight to strut and I am not sure how the wider tire will fit. Any advice?

 

The new wheels will move the centers of the tires outboard by 9 mm and the new tires will stick inboard about 10 mm more. If possible,try a new wheel with a used 245/45-17 tire from a tire shop. In working out my new fitment,I bought a damaged wheel in the dimension I wanted and had a used/throwaway tire installed. Keep in mind that the 245s will raise the car slightly and reduce acceleration a bit.

 

Thank you, that is a really useful tip!