Ive seen a 40x17" tire on a 16x7" rim. It was a spare, and looked odd, but was better than nothing. Given that it was a tall tire, it helped with the angle of the sidewall. Ive personally run 36x13.5 on 15x8 wheels with no complaints for many miles.
Wow, hadn't expected that. I was thinking somebody told me once that a good rule was between 2" and 4" difference between rim and tire.
I had a set of 31x10.50s once that somebody had mounted on 10" wide rims. Funniest looking things I'd ever seen, practically looked liek a trapazoid in profile.
Same PO had spraypainted these CHROME rims black w/o any prepwork, lol.
(I got 'em from Metto but he'd never admit to doing it)