was a persistent, but apocryphal, rumour to the effect that "RD" indicated race developed. In fact, "R" appears to have indicated reed valved, "D" the twin (or double) cylinder models and "S" the single-cylinder models. The RD family would be developed through the 1970s and 1980s, gaining solid wheels, water-cooling, YPVS, and other newer technology 'til they had little in common with the original variants (before being supplanted by the TZR). The RS family was produced for many years in a large number of variants by Yamaha and then Escorts Limited in India without losing its resemblance to its progenitors. In addition to the RD and RS standards, Yamaha also manufactured small standards with stamped steel frames and rotary disc-valved motors such as the Yamaha FS1, and step-through V-50 and V-80 designs. Its Enduro trail bike was replaced by the DT models. Not until 1976 would Yamaha answer the other Japanese brands with a multi-cylinder four stroke of their own. The XS-750 (and later 850) a 750cc triple cylinder machine with shaft final drive was introduced almost seven years after Honda's breakthrough bike. Yamaha's first four-cylinder model, the XS-1100 followed in 1978, again with shaft drive. Despite being heavier and more touring oriented than its rivals it produced an impressive string of victories in endurance racing. The 1970s also saw some of the first dedicated off-road bikes for off-road racing and recreation. Yamaha was an early innovator in dirt-bike technology, and introduced the first single-shock rear suspension, the trademarked "Monoshock" of 1973. It appeared in production on the 1974 Yamaha YZ-250, a model which is still in production, making it Yamaha's longest continuous model and name. Yamaha continued racing throughout the 1960s and 1970s with increasing success in several formats. The decade of the 1970s was capped by the XT500 winning the first Paris-Dakar Rally in 1979. 1980s: diversification and innovation By 1980 the combination of consumer preference and environmental regulation made four strokes increasingly popular. Suzuki ended production of their GT two stroke series, including the flagship water-cooled two-stroke 750cc GT-750 in 1977. Kawasaki, who had considerable success throughout the 1970s with their two-stroke triples of 250cc, 350cc, 400cc, 500cc and 750cc ended production of road-going two strokes in 1980. Yamaha bucked this trend and continued to refine and sell two-strokes for the street into the 1980s. These bikes were performance oriented, water-cooled twin cylinder machines, designed to achieve