Advanced dimensionally stable PET, commercialized as DSP(TM1) fibers for tire reinforcement, and rayon treated cords were subjected to laboratory tests simulating tire cure and subsequent field service. The resulting cords were shown to be similar to those removed from typical radial tire bodies. Subsequently, mechanical properties were measured using a variety of tests and test environments (humidity and elevated temperature). Analogous to conventional PET tire yarn, all of the advanced dimensionally stable PET's have superior strength to rayon. Possibly more importantly, the advanced PET products have greatly improved dimensional stability, with one product (1 X 40) exhibiting similar properties to rayon cords in radial tire bodies without the need for PCI. Body cord weight reduction ratio depends on the tire design, tire manufacturing process, and the sensitivity of tire performance to specific cord properties.