I can only guess, but late 70's, and then the onslaught of the 80's, with the bad-ass Japanese Schwinns, Miyata's gems, Lotus, Fuji, Nishiki, etc. and the output from the Panasonic National plant. Statistical Process Control bikes, and then The Wide World of Sports brought us Dave Scott. The fall of Suntour, the rise of Shimano, and the rest is history.