A track assembly 30 for converting a wheeled vehicle 10 into a tracked vehicle. The track assembly 30 has a longitudinally adjustable support frame 40 having a motive source 170 with a drive sprocket 190, a plurality of support rollers 80, 84, 88, a tensioning assembly 90, and an endless track 200. The track assembly 30 is connected to a vehicle 10 by articulated, resiliently biased mounting assemblies 210, 410. Each mounting assembly 210, 410 includes a first attachment member 212, 412, a link 250, 450, and a second attachment member 300, 500, with the first attachment member 212, 412 configured to be removably attached to a position on a vehicle 10 where a wheel axle attached to an internal drive unit 19 would normally reside but which has been disconnected from its control lines and removed, and with the second attachment member 300, 500 configured to be connected to the support frame 40. The motive source 170 of the track assembly 30 is connected to and controlled by the same control lines 18 that were previously connected to the internal drive unit 19.