I've just fitted some 18's on my car the golf gti onces in anthricite with a 215/35/18 on them and there mint.
Not changed the speedo and it corners just as b4 on the 16's (as mine is the pre facelift fr tdi). They don't rub
on the arches on the stock sus set up but it doesn't look like it's on stilts either. But i have been told that if u
lower it, it can rub but only on the front the backs are surppose to be fine unless you drop it past 40mm.
you got any pics mate?