Hi everyone,
for those who stumble on this post, maybe this will help.
This is possible wheel and tyre sizes for A6 C7 4G:
225/60 R16
225/55 R17
225/45 R18
225/50 R18
245/35 R18
245/45 R18
255/45 R18
245/45 R19
255/40 R19
245/35 R20
255/35 R20
And one thing in addition ... when going on 19 and 20 inch wheels, there must be intake fuel pipe protection aluminum cover mounted and grounded to the chassis. At least that is the case on MOT checks in Germany and Croatia. There is a picture on this site: https://www.motor-talk.de/forum/tankschutzblech-bei-radgroessen-ab-19-zoll-t5922979.html?page=16
