http://www.biketiresdirect.com/produ...700c-road-tire

I have a friend whose just short of 6 foot and probably 225, and he runs 28s. I have the 25's of those, and I'm at 180, Ive never had a problem, I love them.

http://www.biketiresdirect.com/produ...ross-700c-tire

If you really want to go bigger.