Ever the inventors, SunTour introduced the radical S-1 design just when its fortunes were at their lowest ebb. It was an updated version of the 1938 Nivex and 1955 Altenburger designs, mounting on a braze-on under the chainstay and using a horizontal parallelogram. SunTour went one step further than these hallowed forebears and incorporated the rotating cam indexing system from the Bridgestone Klimatic.
Designed for commuting bikes, it all looked quite well thought out - but a SunTour system that demanded special unique frame fittings was never going to catch on a world in which Shimano was now totally dominant.
This example is a short pulley cage S120 version.