A suspension system having an axle, at least a portion of which is made of a composite material. In a described embodiment, a suspension system includes an axle assembly which has a composite axle portion. Metal spindles are attached at each end of the axle for mounting wheels thereto. Two beams may be attached directly to the composite axle portion, to a sleeve overlying the composite axle portion, or to an axle seat attached to the sleeve or directly to the composite axle portion.