|Lower/Upper pully wheels. Is there a difference? (X-Post)||Kellum1969|
Jul 29, 2002 1:13 PM
|I'm cleaning my Campy rear derailluer, and after finally getting all the grease off them, I notice one says Lower and the other Upper. To me, they look the same, and unlike my XTR RD on my Mt Bike, one does not seem to have play.
Nonetheless, does it matter where each goes? And if the answer is yes, which is consider the lower (the one farthest from the derailluer body)?
Jul 30, 2002 9:33 AM
|...have a similar differentiation. Upper pulley runs on a ceramic bushing which offers some lateral float to compensate for imperfect derailleur alignment. Lower pulley
runs on a simple sealed bearing which affords no float.
|General jockey wheel observations||Jofa|
Jul 31, 2002 1:45 PM
|I trawled the Patent Office archives for some information on this a while ago, to try and resolve a thread dispute which had gone nasty. It was largely inconclusive (there are a huge number of patents pertaining to Derailleurs), but I found some interesting asides (all is from memory: I lost the links to the records, but they are all presumably still there):
The first mention I could find of a floating (axially) jockey wheel was in an application by Sachs, sometime in the early 70's. Its mechanism was overcomplex, involving a toothed surface sliding against a spring over a fixed jockey body, and I don't remember ever seeing it in production.
The next occurences I could find were in a litany of applications by Shimano, a little later: the mechanisms were varied but simpler, and the stated intention was to allow "pre-shifting" (that is, to shift when coasting, such that the gearshift will occur when pedalling is resumed- ie, at the approach to a hill). This was all before indexed shifting. I have a loose memory of these derailleurs, especially as it was my conviction that floating jockeys predated indexing, which prompted my research.
These applications persisted in various forms until indexed shifting (of which a huge number of designs were proposed: SunTour eventually did it first, without floating jockeys), and then peted out. The only subsequent mention I could find is in Shimano's marketing, wherein they claim that the function of the mysterious floating jockey is to allow "overshifting", and tolerance to misadjustment. I wonder whether the marketeers speak often to the engineers, as neither of these claims make much sense to me; floating jockeys would seem to be unnecessary now we can change gear from the handlebars. In any case, other rmanufacturers followed and now they are a standard feature.
Which is not much in answer to your question, though it may be diverting to others here who are interested in such arcane concerns. I'd bet you could put your jockey wheels back any way you fancied without the sky cracking in two: but, yes, "Lower" means the lowest one.