A coiled tube injection drive assembly having a pair of opposed, upwardly extending movable carriages positioned in opposed fashion so that portions of tubing may be vertically disposed and engaged between the movable carriages, each of the movable carriages comprising a respective gripper chain and associated bearing chain assembly, where the bearing chain is mounted on sprockets that are coaxially disposed between spaced apart gripper chain sprocket wheels so that the bearing sprockets are mounted about the same shafts as the gripper chain sprockets, without being directly mounted to rotate with those shafts. Other assembly features and related methods are also described.