At 5' 7" I would say you would be looking at riding a "small" size versus a medium. The geometry of the 29ers are so different than smaller wheeled bikes that I know people who would be obvious size large, but go with medium because of the fit of the bike as a result of the dimensions of the design, including stem length. Like someone else on this thread said, the only way to really know is to try before you buy. Good luck!