Originally Posted by
smd4
The B screw adjustment? Seriously? That has absolutely nothing to do with sizing a chain.
I did not say that the B screw adjustment has anything to do with sizing a chain. I only said that it affects the angle between the ground and the line between the two RD pulleys, especially since (as you correctly pointed out) the Shimano Dealer Manual calls for them to be lined up "perfectly vertical."
Originally Posted by
smd4
It almost sounds like you don't know what the B adjustment screw is for.
B screw adjusts the distance between the guide (i.e., top) pulley and the cassette. Depending on the chain tension, it also affects the aforementioned angle between the ground and the line between the two RD pulleys.
Originally Posted by
smd4
And of course the cassette has to be within the limits of the derailleur capacity. Duh.
And if the cassette is not within the official specifications of the RD (e.g., GS model with a 12-25 cassette) but still shifts fine, it may not be possible to have the two RD pulleys perfectly vertical.