Originally Posted by
Kontact
Assuming a typical Shimano derailleur and small/small vs big/big chain lengths, what is going to cause the shifting quality to be affected by the angle and tension of the jockey pulley cage if the indexing, stops and B settings were made correctly?
Chain length, even a link or two, will affect the wrap and the position of the jockey cage. It's kind of hard to describe, but a chain will often shift better with a link added or removed. There's always an optimum, despite the fact that often times a range of chain lengths will actually work. It's mostly in the smaller cogs in back that the differences are obvious.
AFA the why, I don't know and don't frankly care. There are a lot of aspects of bike mechanics where experience trumps theory. This is one.