Originally Posted by
SoSmellyAir
I did not say that the B screw adjustment has anything to do with sizing a chain.
Then I don't know why you'd bring up the B adjustment in a thread specifically about sizing chains, in response to a post specifically about sizing chains for a specific drive train.
Originally Posted by
SoSmellyAir
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."
My delay in responding to this post is because I wanted to be
absolutely sure about this before I called out BS, so I had to wait until I got home before working on my bike. Now that I've done so, and run the B adjustment screw--all
11 mm of it--all the way in and all the way out, with my chain on the big ring and smallest cog, I can safely say, and without reservation,
BS! Moving the screw those miniscule 11 mm one way or the other
does not move the derailleur cage at all off the vertical.
Originally Posted by
SoSmellyAir
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.
You're correct on the function of the B adjustment screw. Please see my "BS" comment above concerning the rest of this statement.
Originally Posted by
SoSmellyAir
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.
I only specifically referenced the Dura Ace 7700 drivetrain. Of course, this same setup was the same for all my Shimano road bike drivetrains going back to 1986.