Abstract: A tire building machine of the expandable bead lock type employs an elastomeric specially shaped radially expanding bead lock including a shaping and turning bladder which includes an air passage system therethrough. The elastomeric bead lock is confined for radial expansion in an annular outwardly opening chamber in the form of an isosceles trapezoid in radial section with the elastomeric bead lock being of similar configuration and expanded by direct application of air pressure within the chamber. The configuration of the annular chamber and the bead lock compensate for stretching of the bead lock upon enlargement. The edges of the bead lock at the axial sides of the chamber are undercut for flexibility while the walls of the chamber are specially coated to maintain the seal. The bead lock incorporates interconnected metallic segment side plates which not only limit the stroke of the moving seal but insure stability axially of the bead and provide the desired concentricity.