SunTour or SR Suntour is a Japanese manufacturer of bicycle components. Begun in 1912 as Maeda Iron Works Company manufacturing freewheels and sprockets, the company began producing their version of the French pull-chain, rod-guided, touring derailleurs in the 1950s. In the 1960s SunTour invented the slant-parallelogram rear derailleur. 

Nobuo Ozaki, the head of product development at Maeda, invented the slant parallelogram rear derailleur in 1964 and Maeda obtained worldwide patents on the design. For the next 20 years, Suntour produced technically superior derailleurs. Suntour's slant parallelogram broke the image of Japanese components as being cheap copies of European components.

In 1985, Suntour had about 50% of the U.S. derailleur market for quality bicycles. Over the decade, Suntour introduced more 120 new rear derailleurs and they still fell victim to the fast changing market. Suntour was too small to maintain the research and development needed to survive

The article Sunset for SunTour by Frank J. Berto is the best read for the rise, and then fall, of the company which can be read here.  SunTour as it was once known ceased to exist some time in the 1990's before the name was sold.