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From what I've read SRAM solved Boost offset by making Boost and non-Boost chainrings. So the cranks are the same, you need to buy specific chainring.

What about Shimano? Is offset within cranks or within chainrings?

I am asking because I consider buying crankset (SLX-FC-M7120-B2) and chainring for completely different crankset (22T for M8000-XT), BCD should work, but if chairings are offseted as in SRAM, this combination will not work.

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    Can you give more info on what setup you are trying to achieve? You are mentioning SLX-FC-M7120-B2 which is a direct mount 2-ring crankset. But in the next sentence you are stating that you want one 22T chainring on it and for some reason you are comparing the BCD... It is not very clear Nov 18, 2022 at 18:33
  • @ArtGertner, thank you for pointing this out. I looked at the picture, I saw bolts (?) so I assumed the chainrings are mounted traditional way. So my example here is wrong, but the genera question still holds -- basically I would like to buy some 26/36T crankset and replace the small chainring to 22T. So this leads to -- are chainrings for Shimano in two flavors (Boost and not) or just one? Nov 18, 2022 at 18:59
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    my interpretation based on what's available for purchase is that the chainrings are all the same and the crank arms are what come in standard, boost, and super boost flavors.
    – Paul H
    Nov 18, 2022 at 19:43
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    I second @PaulH on this, Shimano advertises crank arms as compatible with different O.L.D (standard, boost, superboost). Chainrings are all the same. What O.L.D are you going for? Nov 18, 2022 at 19:45
  • @ArtGertner Honesly you puzzled me? Boost one (regular, no super), but I don't know how it translates to OLD (3 mm I guess). Nov 18, 2022 at 19:55

1 Answer 1

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Shimano chainrings are all the same regarding offset. The difference is in the cranks, which come in x100 / x120 / x130 varieties (eg. FC-M7100 vs. FC-M7120)--each of which corresponds to a different chainline (49-52-55mm). As Art Gertner helpfully points out in a comment, the M8000 inner chainring does look to be compatible with the new 12s direct mount chainring system. The inner chainring is mounted to the outer using four standard chainring bolts. However, there's no guarantee the bolt pattern is still the same as before--it's still 64mm I believe, but Shimano uses this offset, asymmetrical bolt pattern, which could have changed between the generations. Also, the documentation for the cranks does state the only acceptable combination is the stock 36-26t, but I do not know whether this is due to a dimensional incompatibility or just the fear of decreased shift quality when using a different combo.

Lastly, 22t paired with a 36t might not work too well. Shift ramps won't line up, and that is quite a large tooth count difference.

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    Interface from crank to higher chainring is direct mount. Then lower chainring is bolted to the higher chainring. Basically it is the worst of the two worlds. Look up part numer WP-Y0JB98010 and search for images. You will get the idea. Nov 18, 2022 at 19:46
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    Thank you very much. As for 22-36T jump, Shimano actually makes such crankset but it low-level and chainrings are fixed permanently. That's why I am looking for something when I can change individual chainrings when worn out. Nov 18, 2022 at 19:58
  • For SLX-FC-M7120-B2 mentioned in OP's question, there is dealer's manual available. si.shimano.com/en/pdfs/dm/MAFC002/DM-MAFC002-11-ENG.pdf On page 27 it states that only possible combination is 36T 26T. Then again, manufacturer's recommendations are often conservative. Nov 18, 2022 at 20:10
  • As a side note, this bums me out because I would looove to use on a boost chainlink on my super boost bike since 90% of my pedaling is steep climbing.
    – Paul H
    Nov 18, 2022 at 20:42
  • @MaplePanda what are you referring to when you state about Shimano cranks, "which come in x100 / x120 / x130 varieties?” What aspect of the crank do those numbers represent?
    – Jeff
    Nov 19, 2022 at 4:14

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