The trolley includes a member which supports the shoe of a loaded rack. The member has a horizontal limb which extends beneath the shoe and first and second housings each having vertically adjustable casters. One of the housings is connected to the member while the other has a clamp for attaching the housing to the horizontal limb of the member. As the casters descend, the shoe rises with resulting raising of the foot from the floor on which the rack rests.