Same as my old GT, which must have come with 18's from factory.
I then moved to one which probably had 17s from the factory and came with a spare. I changed to 18s. and still have the spare.
On both occasions, with and without the spare, none of the crap underneath sat flush with the carpet! I will buy another 18 inch at some point - this will make the carpet stand poud a little but nothing seems to fit flush anyway so, who cares!?
All this talk of 406s made me sick and I think I am about to vom again, must dash.