Shimano first introduced Dura-Ace 600 group sets in the 1983 as an alternative to more expensive recreational bicycle accessories. Components included derailleurs, side pull brakes and gear sets. Affordable pricing resulted in a degree of popularity that eventually attracted competition cycling enthusiasts. As a result, Shimano expanded the Dura-Ace 600 line to include dual shift levers, multi-speed gear sets and bottom bracket hubs. By the early 1990s the original 600 series had been discontinued in favor of the XT and Ultegra lines.
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Dura-Ace 600 was Shimano's second attempt to produce a top-of-the-line parts group. The first Dura-Ace AX line was not well received, giving way to the 600 series in the early 1980s. As with many new products, once in regular use, minor problems emerged. In a sense, consumers were guinea pigs and problems had to be addressed if the manufacturer's efforts were to prove out. Improving the reliability of 600 parts soon rectified minor problems. Today, Dura-Ace parts feature the improvements Shimano made after introducing the 600 series.
In 1984, Shimano introduced the first successful indexed-shifting system as an addition to the 600EX lineup. It consisted of a 6-speed gear system with indexed shifters mounted on the down tube of the bicycle. Indexed shifters reduce shift cable tension, which in turn reduces the adverse effects of friction caused by improper cable adjustment. The innovation made for a more forgiving 6-speed gear system.
Shimano expanded the 600EX series to include 7-speed and 8-speed gear sets. By the late 1980s, the popularity of the gear sets once again presented many Shimano consumers with a compatibility issue: Specifically, the limited application of certain original 600 components. Shimano resolved this by developing a derailleur that featured alternate cable routing. This meant consumers could continue to use their older Dura-Ace 600 shifters and cables. Later developments included hyper-glide sprockets that allow the chain to engage adjacent sprockets simultaneously when shifting. The chain meshes with the next sprocket before it disengages from the first. This resulted in smoother and faster shifting of Shimano 600 gear sets.
Shimano's original intention of providing affordable accessories took on a new light as popularity of the newer Ultrgra and XT series gained momentum in global markets. The manufacturer did not want to abandon the 600 series completely and force many consumers to by new components. The answer was compatibility. Today, Shimano produces non-series components, including brake levers, brakes and cranksets that are compatible with older 600 group sets.