A suspension system for supporting a ground engaging member relative to a frame is provided. The suspension system includes a torsion axle assembly including an arm, an axle coupled to the ground engaging member and connected to the arm, a shaft connected to the arm and a tube that is connected to the frame. The tube is configured such that at least a portion of the shaft is received in the tube and supported by the tube for rotation relative to the tube and the frame. A lockout assembly includes a coupling mechanism that is selectively operable to fix the shaft against rotational movement with respect to the tube.