I have tried to follow ParkTool adjustment tips for the B-screw of the rear derailleur (other company's tips are similar) , but I fail to detect the condition "the upper pulley rubs the largest cog".

I have completely unscrew (removed) the B-screw, but even shifting from the second largest to the largest cog shows no interference.

I can, of course, make the upper pulley rub the cog, if I manually rotate the rear derailleur towards the cog. The problem is that the adjustment of the B-screw cannot reproduce this symptom.

Is that normal, or should I worry my rear derailleur was mal-installed?

For your information, the instructions I have followed for the B-screw adjustment are the following:


EDIT: I think it may be a chain length problem, as if the tension was reduced (longer chain), the upper pulley might touch the cog depending on B-screw adjustments. I will check the equations to calculate the chain length and compare against the existing chain.

1 Answer 1


Well, I have removed the derailleur from the hanger, put the B-screw half-way in, reattached the rear derailleur, and the noise of a maladjusted B-screw appears.

I have followed ParkTool guidelines, and now it is properly adjusted: 1/4 of turn from the cassette/upper pulley rubbing position.

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