The invention relates to a self-propelled, wheeled irrigation vehicles (10) that may be converted into a multi-track self-propelled irrigation vehicle (60) using one or more track assemblies (62). Each track assembly (62) includes a carriage (70) with frames (92, 94) that support a plurality of pairs of idler wheels (74, 76), and pairs of bogey wheels (80, 82, 84). A portion of one of the frames (94) is telescopically received within a portion of the other frame (92), so that the frames (92, 94) may move relative to each other in a linear fashion. A tensioning apparatus (212) is connected to the frames (92, 94) so that the frames are adjustable relative to each other. Each carriage (70) also includes a hub support frame (90) that is connected to one of the frames (92) in an offset manner. The hub support frame (90) includes an aperture (132) that rotatably receives a spindle (262) of an adaptor (258). The adaptor (258) includes a peripheral flange (264) to which a segmented sprocket (86) may be connected, and a ring extension (268) that is able to be connected to an existing wheel hub of an irrigation vehicle whose drive wheel has been removed. A flexible endless track (88) is entrained about the wheels (74, 76, 80, 82, 84) and the sprocket (86). The track assembly (62) may be provided with one or more cleats (278) that are removably connected to the flexible, endless track (88), and which include a ground engaging member (281) that serves to increase the traction of the endless track (88).