Rim Choice with Dr. Diff's 13" Brakes

72BluNblu makes a really good point that a lot of people are tempted to ignore. Even if you could pinch a 265 on there, it’s pretty likely that you wouldn’t see any performance benefit since it requires distorting the sidewall and compromising the contact patch. You will also get extra rotating mass and probably some extra cost too.

Personally, I’d suggest erring on the smaller side of the acceptable tire sizes for your wheel width. So with an 8.5, a 255 is about the max useful tire (they really want a 9” wide wheel IMO) and 245 section is probably closer to optimal. As a bonus, it will give you a better shot of clearing everything without rubbing and pretty much anything modern that you put on there will look huge compared to stock and provide a massive improvement in grip too.