A trailing axle suspension system is disclosed comprising an auxiliary chassis, an axle suspension system suspending a trailing axle from the auxiliary chassis, and an auxiliary chassis system suspending the auxiliary chassis from the chassis of a motor vehicle. With the auxiliary chassis suspension system including a pair of suspension arms supporting the auxiliary chassis for pivotal movement and adapted to be pivotally connected to the motor vehicle chassis. And with the axle suspension system and auxiliary chassis suspension system adapted to cooperatively establish the auxiliary chassis and trailing axle in a stowed condition on the motor vehicle and establish the auxiliary chassis and trailing axle in a deployed condition at a location rearward of the motor vehicle chassis and then forcibly cause the auxiliary chassis to help support the motor vehicle chassis with the trailing axle. And wherein the auxiliary chassis suspension system includes a load-bearing member that is separate from the pivotal support of the auxiliary chassis rigidly joining the suspension arms and adapted to engage the auxiliary chassis in establishing the deployed condition and bear a major portion of the force causing the auxiliary chassis to help support the motor vehicle chassis with the trailing axle.