Pulley alignment of Shimano derailleur

Question

I noticed a misalignment between the two pulleys on a brand new Ultegra R8000 derailleur. It’s less convincing on the photo than in real life, but still very much visible. I came across this discussion, where they start off with a similar observation, but switch to noise mitigation strategies pretty soon. I also came across this Shimano manual where the bottom figure on page 12 shows the bottom pulley at a slight angle with respect to the other one and the cogs, very similar to my photo. So while I’ve concluded that this is not a faulty part, I do wonder why they would design it that way. I would expect this to wreak havoc on the chain, compared to a perfect alignment, so what’s the benefit?

PS: Both pulleys are firmly installed, don’t wobble, and turn like they should.

derailleur rear shimano

PS: Both pulleys are firmly installed, don't wobble, and turn like they should.

Lien028 · Answer

Upon initial inspection, the issue described may seem alarming. However, the newer Shimano derailleurs are slightly bent and twisted to aid in shifting performance and meeting the ever increasing demands of larger cassettes.
For instance, the XTR M9100 derailleur is slightly bent and twisted and angled in such a way that the lower pulley wheel is facing towards the chainring. This helps when shifting down the Cassette and prevents damage to the pulley arm when the RD is at the 51T cog of the cassette.
In a nutshell, the slightly bent and twisted cage aids in shifting up/down larger cassettes and mitigates the damages of cross-chaining (which is inevitable on 1x drivetrains).

Pulley alignment of Shimano derailleur

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