Fatbike hardtail mountain bike type mens model 2017 series cube nutrail frame material aluminium frame alloy 6061 aluminium frame characteristics internal cable routing triple butted bike frame sizes inch 21 17 19 18 inch bike frame sizes cm 43 53 38 48 46 cm headset fsa orbit 15 zs suspension system air suspension fork feature compression suspension fork technologies rock shox poploc rock shox motion control gear system with derailleur num