A suspension assembly for a snowmobile is provided that rotatably supports a closed-loop track in the rear tunnel of the snowmobile and also supports both vertical and horizontal travel of said closed-loop track during suspension system travel. The suspension assembly includes at least one elongated ground contact that supports rotational travel of the closed loop track and at least one swing arm angularly disposed in the closed-loop track and having a front end portion pivotably coupled to the rear tunnel and a rear end portion coupled to the at least one ground contact. In the preferred arrangement, a front resilient member is arranged to bias against displacement between the chassis and the at least one ground contact during suspension assembly travel and a rear resilient member arranged to bias against displacement between the chassis and the swing arm during suspension assembly travel. A tensioner couples the rear end portion of the swing arm to the at least one ground contact. The tensioner is extendable and retractable during movement of the suspension assembly to maintain the closed loop track at a generally uniform tension during assembly movement.