An annular tire building drum having an infinitely variable width for building portions of tires having various widths in a tire building machine includes a hub portion, an annular fluid expandable tube element supported on the hub portion for movement therewith and a plurality of pairs of shoes supported on an exterior surface of the tube element for movement therewith in a radial direction upon expansion and contraction of the tube element. The shoes define an annular tire building surface which is movable in a radial direction upon expansion and contraction of the tube element. Piston means is supported by the hub portion for moving one of the shoes of each of the pairs of shoes in a first direction parallel to the axis of rotation of the drum and to effect movement of the other of the shoes in a direction opposite to the first direction to thereby infinitely vary the axial width of the building surface. Stop means is provided for limiting the axial movement of the shoes. The stop means is adjustable to allow the axial width of the tire building surface to be infinitely variable between a predetermined minimum width and a predetermined maximum width.