Csubi are you talking about hub spacing? Different size spacing for different size wheel sets. 2 different sizes available for that bike, 148mm for the 27.5"/29" and 197mm for the 26" if I'm not mistaken. I found that info on the WW website under Hydra Frameset only section. Maybe having the hub size listed in the whole bike category and isn't a big deal if your buying a complete bike but if building it up yourself I would want to know to that info preorder my parts correctly.