There are a few people that have run 275's it really depends on the wheel and offset on if it will clear and also if you don't mind rolling/pulling the fenders. I believe most I've seen were on +40 to +45
I'm not going to dig through and find the specific post but there are a few in the meaty tire thread here:
https://www.ft86club.com/forums/showthread.php?t=41083