An endless track assembly that mounts to a wheeled vehicle. The assembly provides 1) a track suspension having fixed or adjustable, independently biased sets of idler wheels to vary the track contour without affecting track tension, 2) an eccentric bearing housing at a drive sprocket controls track tension, 3) a contoured peripheral edge at the drive sprocket prevents ice and mud buildup, 4) rubber-coated, plastic idler wheels facilitate track movement, 5) a multi-vehicle compatible adapter mounting plate accommodates a variety of vehicles, 6) a rotation limited torsion coupler and/or rotation limiting coupler arms prevent track contact with the vehicle, 7) a locking steering arm coupler prevents loss of steering control, 8) shaped track lugs and channels clear and direct debris away from the track suspension and drive assembly, and 9) a center, spring biased coupling suspension stabilizes and enhances the contour following and load handling capabilities in the center region of the track. The improved suspension particularly supports sets of idler wheels in pivotal relation to the track support frame and resiliently biases a pre-tensioned rocker arm that links adjacent suspension arms mounted to the adjoining idler wheels. Suspension arm movement induces expansion and contraction of tension springs coupled to the rocker arms to augments shape changes at the track contact surface to optimize traction and steering control.