A rotatable tire building drum 10 has a pair of axially and radially moveable bead locks 20 and a radially expandable center building deck assembly 40 with two sets of deck plates when expanded forms a 360 degree solid deck surface. The deck plates have been sized to abut when fully expanded to form a solid 360 degree building surface to support a tire carcass 2. The two sets of deck plates are divided into a first set of even deck plates and a second set of odd deck plates, arranged in a sequence of at least 6 or more circumferentially adjacent abutting deck plates 1, 2, 3, 4, 5, 6 in an expanded state. In a retracted state, the first set of even deck plates 42 moves radially inward of the second set of odd deck plates 44, the first set 42 underlying the second set 44.