Why not just put the largest tire that will fit on the wheel and clear the body, and put the most rubber on the road?

You can really tell this when you put oversized tires on a 4X4...We put them on our old Bronco..and the car really slowed down...

However, at the size you are contemplating for your Audi...it shouldn't matter that much.<p><a href="http://registry.audiworld.com/audi/registry/details.asp?car=3821"><br><br>
<img SRC="http://pictureposter.audiworld.com/AudiWorldPics/2000/ss_s4sig1.jpg"<br><br>
Steve S.
00 Nogaro S4
NorCal Audi Club
http://www.norcalaudiclub.org

Height will be slow at low end and higher at top end,it is like changing the running gear. Width is where you get the bigger patch on the road but will not change anything other than weight.

Overall diameter effects are minimal on changing final drive ratio