Welcome to GC from maine. I just put 4 new Kenda K587 Bear Claw HTR's 26 x 11 x 12 on all four. The actual inflated diameter is 26.4". Plenty of room, but because they are wide, I put Mair over fenders on too. I think many of the guys run 27" tires without any lift. I'm not sure about 28's. They will chime in soon I'm sure. Much of anything over 27" dia. and most of the guys do some clutching mods to maintain the low end pulling power.