In the late 80's and early 90's, bike companies were pushing the boundaries and challenging the preconceived notion that a mountain bike had to be built in the classic double diamond shape. The Japanese manufacturer, Koga-Miyata was among the companies challenging the norm. Other brands experimented with elevated chainstays but the unsupported bottom bracket created an incredibly flexible frame. Koga-Miyata approached the problem with a sizable gusset welded from the bottom bracket to the down tube. This gusset made the Ridgerunner Alloy one of the sturdiest alloy elevated chainstay designs.
Special thanks to The Pros Closet
for the information and original photography.