In the 1960s SunTour invented the slant-parallelogram rear derailleur. In the early 1970s, demand created by the bike boom in the United States far exceeded the capacity of European manufacturers. SunTour and Shimano filled the void. While both companies provided products for all price ranges of the market, SunTour focused on refining existing systems and designs for higher end products, whereas Shimano paid more attention to rethinking the basic systems and bringing out innovations such as index shifting and front freewheel systems.
SunTour initially did not sell complete group-sets, so instead teamed up with other parts makers, such as Sugino(for cranks), and Dia-Compe(for brakes), so it could sell a complete line of SunTour branded components. These were good value for money, but didn't have the prestige of Campagnolo, or the innovations of Shimano. And were another set of non-standard parts for dealers and mechanics to handle.
SunTour was the first component maker to make parts especially for mountain-bikes, the Specialized firm in California fitted these parts to its early mountain-bikes of the 1980s, and together both firms were very successful in the American market-place. By the late 1980s Shimano entered the MTB field, and beat SunTour on price and marketing. Profits of all Japanese firms were hit by the sharp increase in the value of the Yen, during the 1980s.
Despite the quality of its parts, and innovative designs, Suntour was unable to compete with Shimano.
SunTour suffered from the devaluation of the Yen in 1985. They remained in the market until the mid-1990s, but withdrew from the American market because they could not compete with Shimano. The SR Suntour brand has recently returned to the market (as of 2004) under new ownership.