A power transmission belt having a body with a length, an inside, an outside, laterally spaced sides, and at least one rib. The body has a compression section, a tension section, and a load carrying element between the inside and outside of the body and extending in a lengthwise direction. The load carrying element is made from twisted polyester fiber filaments having an ethylene-2,6-naphthalate component and a denier of 4,000-8,000. The belt requires a stress of at least 500 N per rib to effect elongation of the belt by 3%. The belt has a dry heat shrinkage stress between 100 N and 200 N after an initial load of 147 N is applied to the belt and the belt is allowed to reside in an atmosphere at a temperature of 100° C. for 30 minutes.