A suspension assembly for a vehicle having an endless drive track is disclosed. The suspension assembly has a slide frame assembly and a rail extension assembly pivotably connected to a rear portion of the slide frame assembly and pivots about a first axis. The rail extension assembly is pivotable between a raised position and a lowered position with respect to the slide frame assembly. A spring biases the rail extension assembly toward the lowered position. The magnitude of the biasing force of the spring is adjustable. The rail extension assembly can be prevented from pivoting from the lowered position to the raised position independently of the magnitude of the biasing force.