I've got the same problem, and since I've just started riding, I don't want to end up with knee or back problems. My inseam tells me I need a 54-56cm bike, but I keep finding 21-inchers (a tad too small imo.) My friend recommended a 56cm bike to me (i'm 5'9), and I do like the stretch on that better. I'm just concerned about the crotch clearance.

Q: Is it better to get a longer stem on a shorter bike, or a shorter stem on a taller bike?

Waddaya seasoned riders think?