A spun polyester fiber, a drawn polyester yarn, and methods for making them. Polyethylene terephthalate yarn is prepared by extruding a molten melt-spinnable polyethylene terephthalate having an intrinsic viscosity of at least about 0.8 through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn; solidifying gradually said molten spun yarn by passing said molten spun yarn through a solidification zone which comprises (i) a retarded cooling zone and (ii) a cooling zone adjacent said retarded cooling zone where, in said cooling zone, said yarn is rapidly cooled and solidified in a gaseous atmosphere; withdrawing at sufficient speed said solidified yarn from said solidification zone to form a crystalline partially oriented yarn; and hot drawing said crystalline partially oriented yarn at a total draw ratio between about 1.5/1 and about 2.5/1 to produce a drawn yarn having an effective crosslink density (N) between about 10×1021 and about 20×1021 crosslinks per cubic centimeter. The yarns and fibers so prepared may be used to make treated tire cord having high tenacity in combination with improved dimensional stability.