The single-stage building of 0.degree. belted pneumatic tires completely in flat band form on standard building drums, is disclosed. The feasibility of the process rests on the provision of the substantially inextensible metallic or non-metallic belt cords in the form of longitudinally extensible high "soft stretch" tapes. In a preferred version of the invention, the tape is composed of a plurality of cords each having formed therein a multiplicity of undulations which in any given straight length of the tape are substantially planar, the cords being disposed in side by side relation so that the planes of the undulations of each cord are generally parallel to the planes of the undulations of each adjacent cord, and the cords together with a relatively weak and frangible but only minimally undulated stabilizing yarn for the tape being secured to each other and held in their undulating state by a relative weak, chain stitch knitted, frangible stitching yarn or thread. The belt-forming structure is built by helically winding such tape circumferentially of the building drum in the medial region of the still cylindrical or flat band carcass at an angle of substantially 90.degree. to a plane including the common axis of the carcass and the building drum, with the undulations of the cords "on end", i.e. in planes generally normal to the surface of the building drum. Upon the raw tire then being radially expanded into its toroidal form, the stabilizing and stitching yarns break and the cords are straightened out, resulting in the formation of a mono-ply, plural-lead, helical cord 0.degree. belt in the shaped tire. The "soft stretch" of the tape used, i.e. the ratio of the length of the component cords when fully straightened without stretching, to the length of the unextended tape, may be as low as about 20% or as high as about 400%, depending on the extent to which, for any given tire, the belt-forming structure will have to expand radially from its starting diameter on the building drum to the final belt diameter in the toroidally shaped tire. Each cord may additionally be locally weakened at a multiplicity of longitudinally spaced points to facilitate a possible stretching or elongation of the cords after the same have been fully straightened out during the radial expansion of the belt. In any such tape, the component cords must be phased relative to each other to dispose the respective weakened portions of each cord out of lateral alignment with the weakened portions of at least each next adjacent cord, and the weakening interval should preferably be so selected that in the final belt the weakened portions are out of lateral alignment with each other in directions parallel to the tire axis. The full nature and extent of the invention is discernible, however, only by reference to the entire disclosure.