1. A flexible track belt comprising: at least one flat elastomer endless support belt having a centrally disposed inextensible reinforcing ply of circularly wound inextensible reinforcing filaments in a side-by-side relationship therein to form connected loops of substantially equal diameters forming at least one cylindrical ply with filaments individually encased by elastomer; a plurality of removable oblong track shoes circumferentially arranged about the outer peripheral surface of said flat support belt at spaced intervals, said track shoes oriented transversely across said support belt and transverse to the axes of said reinforcing filaments in said support belt, and a plurality of attaching means coupling said track shoes to said support belt, each of said attaching means having an outer belt engaging member and an inner keeper member, each of said inner keeper members having a belt conforming channel recess with a uniform recess cross-section therein, said keeper members arranged at circumferentially spaced intervals about the inner peripheral surface of said support belt and integrally formed with said support belt so elastomer portions of said support belt separate adjacent edges of said keeper means from one another thereby providing a continuous inner surface, each of said keeper members confining in its channel recess the lateral contiguous edges of a portion of said belt having said reinforcing filament encased in elastomer operable to prevent lateral extrusion of elastomer surrounding said reinforcing filaments when said portion is clamped in its contiguous channel recess so elastomer in said portion can be loaded with sufficient force to prevent slippage between said attaching means and said inextensible reinforcing filaments due to a couple formed therebetween as the elastomer is densified by said force.