Oops, mixed up my mms again, yes 22 cm shorter than Sierra.
I could run wider tyres in theory but most of the extra arch width is taken up with 4x4 system, don't forget that the 205 gti is much narrower track, so it is a case of what is left to fit tyres and wheels in, I need et25 / 28 to clear the suspension struts and brakes, if I go et 30 the rims hit stuff, et 20 and things poke out the arches.