A power transmission belt, and more particularly a toothed power transmission belt, comprising a longitudinally extending tensile member composed of one or more carbon fiber cords, wherein the belt exhibits belt growth of not more than 0.1% based on its original length after 48 hours under High Temperature Belt Growth Analysis performed at 100 C., a method for producing such belts exhibiting reduced belt growth, and a method for reducing the angular vibration of a camshaft in relation to a crankshaft in an internal combustion engine wherein the camshaft is driven by a timing belt.