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It's been difficult to locate a new XTR M9100 or XT M8100 with the SGS (long) cage from the few reputable U.S. dealers I buy from where Shimano will honor their warranty. The GS cage versions are readily available. In the past, I know it's been possible to switch cage length on Shimano derailleurs. In fact the Dealers Manual for the above derailleurs has a section describing replacement of the plates that make up the cage but doesn't specifically state its possible to change between GS & SGS cages. The key is whether the main body of the derailleur is different between an SGS cage der and the GS version.

Looking at the Exploded Views of the M8100 GS & SGS versions--they are separate documents, which is different from EV's of older model ders that had one exploded view that showed both GS and SGS cage assemblies on one document, inferring the same derailleur body is used--it appears all part numbers are the same except for the differing cage plates. GS cage EV

Further, comparing the derailleur bodies of the SGS & GS versions, there doesn't appear to be a difference in them. Can anybody confirm they use the same main body for both cage lengths? compare der bodies

I have a source for replacement SGS cage plates for the M8100 and the GS versions of the entire derailleur are available and I wish to run a 1x system with a 10-51t rear cassette which requires the SGS version to be used, sums up my motivation to faff around with this, as the Brits might say.

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  • If I remember correctly, the SGS and GS versions are NOT cross-compatible. The GS is optimized for the 10-45t cassette, whereas the SGS is optimized for the 10-51t. The difference should be in the parallelogram slant angle (also the jockey wheel offset, but that's determined by the cage). I'd imagine it's possible to make it work, but it wouldn't be the "ideal" setup. Don't have evidence for this though--I'll write a proper answer if I find some sources.
    – MaplePanda
    Jan 8 at 3:25
  • This is what I've heard too: differences in the main body between SGS & GS spec'd ders. I've come across similar question to mine in different but less "serious" forums that caution about differences in the body. I also found it curious there are two EV's of the M8100 der on the Shimano site, one for GS cage, one for SGS cage. In the past the two cage lengths were shown on the same EV of a given RD.
    – Jeff
    Jan 8 at 5:27

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They're swappable - we came across the same question, checked the docs and confirm the body is the same. A friend of mine made the same change; but gone from SGS to GS.

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  • @ Baris Atasoy Do you have the link or reference to the docs you checked confirming the bodies are the same?
    – Jeff
    Jan 8 at 5:31
  • Shimano docs, shimano site. I dont collect them as I regularly visit and look something at their site.
    – Barış Atasoy
    Jan 8 at 8:01

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