what is the largest tires that will fit without a lift?

 

I know someone that put 285's under a 4x4 and it's fine. Only rubs slightly on one turn or the other and that's a full lock turn. I didn't look, but that's probably something like the plastic wheelwell or trim that could be trimed. If it is, maybe you could go larger. 285's look good on a stock Excursion, or SD for that matter.