I am in the process of buying a new mountain bike, and am 5', 27" inseam, and weight 100lbs. I want a serious bike, and after researching it for several months, here is what I came up with. The Santa Cruz Juliana (XS frame size) and the Pivot Mach 4 (xs or xxs frame sizes). I demoed both bikes and they are both great. The currrent president of Pivot Cycles used to be the president of Titus Cyles. This does not surprise me as when I went to Moab and rented a bike, the bike I rented there was a Titus Titanium in a very small size frame. That too was a great bike, and the only one that fit me after going to several bike stores in Moab. Hope this helps.