A method of building and transferring a tread 12 or a tread belt reinforcing assembly 14 on a building drum 10 is disclosed. The steps include applying at least one uncured tread component 12, 14 onto a radially collapsible building drum 10, inserting the at least one uncured tread component 12 and the radially collapsible building drum 10 into an open segmented mold 2 wherein a plurality of mold tread forming segments 4 are radially expanded; contracting the plurality of mold tread forming segments 4 pressing into the at least one uncured tread component 12, 14; collapsing the building drum 10; and removing the building drum 10 thereby transferring the at least one uncured tread component 12, 14 into the mold. The preferred building drum apparatus 10 has a portable radially expandable and axially rotatable support means 20; a drive means 30 for rotating the support means 20 about the axis, a plurality of arcuate or straight segments 22 slidably mounted over the support means, the plurality of arcuate or straight segments 22 forming an annular building surface 24; a means 40 for radially expanding and contracting the radially expandable and axially rotatable support means; a means for receiving and accepting the tread or tread belt assembly while mounted on the plurality of arcuate or straight segments 22 mounted onto the portable support means 20, the receiving means 2 being a segmented mold 2 with radially movable tread forming segments 4.