[CR]was:slant parallelogram -- now:silky smooth

Well, I think....

that Brandon is correct. Slant paralleogram derailleurs work better because they follow the cogs more closely, keeping the length of chain between the cog and the guide pulley short and fairly constant. The addition of the upper body spring allows the whole mech to pivot and further helps the pulley track the cogs. There is also the question of 'wrap' or how tightly the chain wraps around the cog before being redirected by the pulley and this is enhanced by slant/double pivot derailleurs. Both these features are found on the derailleurs that can best handle indexed shifting. I may be wrong here, but I think Shimano was the first to combine these features into one unit, having borrowed them from other makers.

But.... While all this enhanced tracking and increased wrap has effectively given the derailleur much better control of the chain, there are a couple of downsides: 1)As Brandon said, there is the issue of setup. With the newer design there is less tolerance of misalignment. Yes, this partly due to reduced cog spacing, but is also because there is less length of chain between cog and pulley to "soak up" the misaligment. Old NR style derailleurs worked pretty consistently even when badly set up or worn out, but then asking a derailleur to friction shift among 5 or 6 wide-spaced cogs isn't asking all that much. 2) having the pulley running so close to the cog and having the chain wrap so far around the cog, there is simply more vibration and noise. A perfectly set up modern system just never seems as fluid as a perfectly set up NR/friction/6-speed/wide-spaced system. I'm not talking about the smoothness of shifting, but just smoothness of operation. The only thing I miss about the old Campy friction stuff (aside from the asthetics and some other intangibles) is the silky-smooth super- quiet operation under pedling load... once you carefully finesse it into gear.

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