Chain out of rail from upper pulley of RD

Discuss light weight issues concerning road bikes & parts.
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Posts: 9
Joined: Tue Jul 03, 2018 1:55 pm

by EthanAlef

I have no idea why my chain sometimes get off from the upper pulley wheel (12T) of my R9150 RD.
I can see the chain tension is pretty high and the B-screw is set such that the upper pulley can be getting apart from the 30T cog.

Do you guys have the same experience of oversized pulley wheel system or big cog like more then 30T?

by Weenie

Posts: 4549
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

It's a narrow wide jockey wheel. You need to time the chain.
If the tension is too high, you won't have enough engagement/chain wrap around the top jockey, and it may skip. A normal jockey might be a better option if you can't fix the tension issue.

Posts: 1892
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Position the wheel so it goes wide tooth/wide gap and narrow tooth/narrow gap. A check of the derailleur hanger alignment wouldn't hurt too.

I like using narrow/wide pulley wheels myself and never have a problem. In fact shifting can improve because of less chain deflection when shifting. Just need to remember that the chain goes a certain way.

My personal tip is not to use the B-screw for chain tension. Only use it to set the pulley-cassette gap to a minimum without touching.

I set chain tension by sizing the chain.

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