Another 3/4 ton question

[Daks]

I replaced the old 16.5 inch rims with 16's as well and the largest tire the they would put on those rims (they are actually like 6 1/2 or 6 3/4 inch width I think they said) was a 285/75 R16. They measure just smaller than 33 inches. I was told anything larger could actually slip off the bear during something as simple as hitting an imperfection in the road such as a minor pot hole. Truth or not? I have no idea, just what I was told...