The message below differs from my experience on a couple of points. My comments are inserted. The NR derailleur was designed in the days of 4 tooth spreads between outer and inner chainrings, and works extremely well with 52-48 chainrings and the like. When riders started using 10 tooth spreads (42-52) this created a big problem for the rear derailleur. If the chain was short enough to not droop when on the small chainring, the upper pulley is pulled away from the freewheel cogs when the chain is on the large chainring, making for the notoriously poor shifting of the NR rear derailleur when on the big ring in front. The 2nd generation SR rear had a redesigend pulley cage that was better suited for the larger chainring differences that had by then become common.
But the problem is solved by the spring loaded upper pivot, which (someone will correct me if I'm wrong) was first made by Simplex. The spring loaded upper pivot allows the derailleur to pivot forward when the chain is on the big ring, which then allows the upper pully to track closer to the freewheel cogs, making the rear shifting just as precise when in the large ring as in the small.
Campy was smart enough to realize this when designing the first Rally derailleur... No, the first generation Rally is basically an NR with a long cage. the second generation Rally is the one with the functional upper pivot. It was a copy of the Simplex long cage derailleurs. But for reasons that will forever remain mystery, they couldn't bring themselves to add the spring loaded upper pivot to the NR derailleur... At the time the upper pivot was added to the Rally, the SR was working fairly well for it's intended application, which was friction shifting over narrow gear ranges. Suntour's slant parallelogram and Shimano's twin pivot designs shifted faster, but in my experience the SRs ran smoother. The extra pulley-to-cog distance made shifting sluggish, but also made the drivetrain run smoother overall. Did this make Campy better? Not really. Preferring Campy because it ran smoother was probably as progressive a mindset as racers in the 40's using the Cambio Corsa because it added less friction. That is to say, maybe there was less friction with the Cambio Corsa but the shifting was miles less efficient than a derailleur. Ditto the SR vs. the Japanese stuff. Once indexing came into use, there was really no room for debate, the Campy design no longer cut it. ....until the first C-Record derailleur was introduced, around 1983 + or - a year. And then, inexplicably, they dropped the spring loaded pivot after a year or so and the C-Record derailleur went back the the same pathetic old design of the NR. No, though this is a common misconception. The upper pivot on the early C was not active during normal operation. The body remained set against a stop at a fixed angle, just like an NR or SR. The only purpose of the upper spring was to make the rear derailleur swing back and stay back when the rear wheel was removed. This was supposed to speed up wheel changes. It was a lot of fuss for little benefit, didn't always work correctly, added (minor) weight and expense and broke very easily. Campy did away with it very quickly, and added a set screw instead. At least the set screw had the benefit of allowing angular adjustment of the body to accommodate varying frewheels and der. hanger designs.
Campy's first twin pivot rears for racing came out in 1990 when they finally made a reasonable attempt at indexing. The system was very Shimano-like. 8-speed cassette hub, twin pivot rear der with the Suntour slant that Shimano had already adopted with the RD-7400 several years earlier after Suntour's patent had expired. Later Campy indexing systems improved as they "coincidentally" became more and more Shimano-like. Notably, virtually all good indexing rears now use Suntour's slant and Shimano's extra spring. A great combination of features that really allows for precise tracking, keeping the cog-to-pulley distance and the amount of wrap quite consistent. Tom DaltonBethlehem, PA
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