I currently have 1.75" tires mounted on Sun Rhyno Lite rims. It's really a much better match to the rim than anything narrower. I had 1.25" tires mounted previously. I think the beads were a bit tight, and that combined with the wiiiiide rims (for those of you who've never seen them in person, Rhyno Lites are better than an inch across) made them the very devil to get on and off. My 1.75" Panaracer T-Servs, albeit with Kevlar bead, have been no problem at all. I wouldn't hesitate to mount tires up to about 2.5" on them.