What size are 2001 S8 wheels 18 x
Perhaps someone else can confirm whether the ET 48 offset can be used on an A6. If so, you'd be much better off with a 245/35-18 tire.
Check the link for details on the possibilities.<ul><li><a href="https://forums.audiworld.com/a6/msgs/110254.phtml">A6/S6 tire options</a></li></ul>



