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Synchro ®
In the late 1980's, Campagnolo needed to respond to Shimano's S.I.S. indexed shifting system. Campagnolo's first attempt was called "Synchro ®."
It was Campagnolo's wish to make a system that would be compatible with its older derailers and other products, to provide an easy upgrade path for existing customers. This was a laudable goal, but turned out to be impractical.
The Synchro (and Synchro 2) down tube shift levers had replaceable, color-coded "indexing discs" with detent notches at different spacings. There were quite a few different indexing discs available for different freewheel models and spacings.
The problem that sank Synchro was cable travel. Campagnolo derailers had always used a very short cable travel from gear to gear. The shorter travel came with higher tension, and these two factors exacerbated issues of cable friction and stretch. As Shimano also discovered, a key to good indexing is long-travel, low-tension cable setups. Shimano also made a misstep with this: its original 1984 Dura-Ace S.I.S. system used a fairly short cable travel, requiring unusually-high precision in associated parts. When Shimano "trickled down" S.I.S. to the 600EX group in 1986, it went with a longer cable travel, which became the standard for the rest of the Shimano line. This led to a decade of incompatibility between Dura-Ace and the rest of the Shimano line, only resolved in 1997 when Dura-Ace went to 9-speed and lengthened the cable travel to match the rest of the line.
Currently, Campagnolo's shifters and derailers use an even longer cable travel than Shimano does.
Synchro derailers and shift levers are incompatible with anything else, and the Synchro system worked so poorly that it is not a good idea to try to set the system up on a bike you intend to actually ride.
