Originally Posted by
Kimmo
I disagree; IMO plastic BB pulleys with no float are always best, but then I have no love for Centeron-G; I think it's stupid. Just learn to adjust the indexing.
Also, bigger ones are quieter and perhaps slightly more efficient; I'd use the biggest that fit in the cage. I've gone +1 on the pulley tooth count a couple of times with no problems. Might affect B-screw adjustment, requiring more screw.
Kimmo- It is my understanding that the float in guide pulleys is to absorb the tolerances that develop in a gear system. Some, often the largest, is the cable tension. But since this variable is so easily "corrected" but other aspects are much more difficult to change, I have always thought that the float was for more then simple cable tension issues. I
IRC when SIS was first introduced many of the aspects that control shifting were still based on the pre-index designs. Cables (Dura Ace first used the same 1.6mm diameter inners as other high quality friction systems did), casing (flat wound/tight spirals but with plastic liners), "classic" cable stops on the frame and downtube levers to name some. (I remember reading in Bicycle Dealer Showcase that there were 17 different design requirements to a fully systemized index design). Then as the early years went along there were "improvements" like encapsulated cable stops (the split stops common now), SIS casing with a many strand "slow" helix winding, 1.2 and 1.MM inner cables, and down tube lever boss cable stops with "on the fly" cable tension adjustment.
All helped "tighten up" the tolerances of the shifting system between the lever and the der. But other manufacturer issues remain to this day. Like rear hanger bolts not perfectly machined (so as you thread them into the hanger the der wobbles/orbits some), Same with the cage pivot bolt as well as the cage it's self, cassette wobble and free hub slop. Then there's the cogs being not fully flat, in fact some are this way by design.
So the guide pulley's float, IMO, is there to help work through all these other aspects that are never perfect.
When Sun Tour and Campy (Sachs) came out with their early systems their upper pulleys were "fixed". The noise and touchiness of their adjustments is but one reason that they were viewed as inferior to Shimano. Many of us mounted float pulleys on these and saw improvements in smoother chain runs and less jumping.
As to larger pulleys- No argument here. Excepting the pulley knock and B screw issues that Shimano is plagued with. Andy.