mountain bikes arent sized as specificaly as road bikes because the rider is out of the saddle a lot he is not as disciplined as a roadie(in body position) he must make physical adjustments that depend on the trail that lies ahead so just give yourself 2-3 in clearance over the top tube and def ride the bike, if its too small your lower back will hurt and you will regret your purchase always remember it is easier to build a bike up but you cant make it smaller