It is known to assemble rollers from a plurality of parts and to rotatably support them on rolling-element bearings. In such prior art designs, a tread body, such as a tire, is either wedged between a split wheel rim whose components are joined together by a friction fit, or is mounted, by molding the material from which the tread body or tire is fabricated while in a fluidous state, on a plastic supporting body which is deformable so that it can be pressed over the outer ring of a rolling-element bearing. Such known designs essentially have a drawback in that they are complex in requiring a great number of individual parts or requiring complex operations for their assembly thereby making them expensive. Long term operability, and reliability, particularly with rough use, is also difficult to attain with such known designs.