Ns bikes zircus dirt jump bikens bikes zircus dirt jump bike optimises the same lightweight and strong aluminium frameset that is used in the movement range to give you plenty of bang for your buck built using affordable quality parts the zircus dirt jump bike is the perfect rig for playing in the city off road or on pumptracks should you wish to tweak your setup from a single speed simply use the optional derailleur hanger and customise your gear range to suit featuresframesetframens