is reinforced with corded fibres (acting as tension members) and the toothed surface is reinforced with a fabric covering. Rubber degrades with higher temperatures, and with contact with motor oil. Thus the life expectancy of a timing belt is lowered in hot or leaky engines. Also, the life of the reinforcing cords is also affected by water and antifreeze, so it is important that belt that can be exposed to water is able to drain the water away quickly. Older belts have trapezoid shaped teeth leading to high rates of tooth wear. Newer manufacturing techniques allow for curved teeth that are quieter and last longer. Manufacturer-specification timing belts may stretch at high rpm, retarding the cam and therefore the ignition. Stronger aftermarket belts will not stretch and the timing is preserved. When designing the timing belt, a wider belt increases its strength however a narrower belt reduces weight and friction. The usual failure modes of timing belts are either stripped teeth (which leaves a smooth section of belt where the drive cog will slip) or delamination and unraveling of the fiber cores. Breakage of the belt, because of the nature of the high tensile fibers, is uncommon. Often overlooked, debris and dirt that mix with oil and grease can slowly wear at the belt and materials advancing the wear process, causing premature belt failure. History Toothed belts were invented in the early 1940s, for use in textile mills. The first known automobile engine to use a timing belt was the American 1954 Devin-Panhard racing car, used an engine converted from pushrods to overhead camshafts through the use of a toothed belt made by the Gilmer Company. This car won the Sports Car Club of America (SCCA) National Championship in 1956. The 1962 Glas 1004 was the first mass-produced vehicle to use a timing belt. The 1966 Pontiac OHC Six engine was the first US mass-produced vehicle to use a timing belt, while the 1966 Fiat Twin Cam engine was the first mass-produced engine to use a timing belt with twin camshafts. Timing chains Metal timing chains have become more widespread in car engines produced since the 1990s, due to the lack of the regular maintenance task of replacing a rubber timing belt. While the chains themselves are subject to minimal wear, lubrication of the chain or failure of the tensioner and chain guides can cause maintenance issues. Early symptoms of