I'll go with CM on trying a 20", I'm 5'11" and I ride a 20.5 and I think that that's the bare minimum that I fit; if money were no object I'd move up to a S&M Black Bike at 21.25 and I'd be perfect. Try it out, I rode some 24"'s at my LBS and I hated them, 20" is more fun with out a doubt.