I am converting my merida silex from fsa omega bcd 120/90 bcd 2x9 to a 1x9 drivetrain. I am keeping the cranks and bottom bracket and trying to only change the rings.

There are not many 120 bcd narrow wide chain rings on the market. I have found a 'stone' chainring from China which is usually for sram 120 bcd. Is this likely to fit my 120 bcd fsa cranks?

Links FSA https://www.bikeinn.com/bike/fsa-omega-pro-120-bcd-chainring/137172323/p

Stone https://m.aliexpress.com/i/32959164753.html?gatewayAdapt=Pc2Msite

1 Answer 1


The FSA 120mm chainrings are an asymmetric bolt circle that is totally unique to the several (maybe only one?) FSA models they come on. It is a standard they made up fairly recently still, and why or what they were thinking is not clear. The chainrings for it are bad quality. Nothing else is compatible. The SRAM 120mm rings are symmetrical.

FSA has made up a couple weirdo chainring standards in recent years that outside support doesn't exist for yet. They're all on a lot of bikes. There is some chance that a third party maker will step in, the situation seems primed for it, but I don't believe it's happened yet. Until then, if you can't get by with the replacement rings FSA offers, you need a different crank.

Edit: As PIER points in the comments, I had this wrong. The Omega 120 BCD cranks use a symmetrical pattern, and it is likely they may interchange with rings intended for the earlier SRAM 120 BCD cranks. I've attempted to delete this answer, but unfortunately it's been accepted, so editing it is the only choice.

  • That is a shame! I will likely convert it back to 2x
    – Tom Vine
    Oct 14, 2021 at 18:14
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    @TomVine The upshot is a pretty large number of those cranks have been sold OEM the past few years (the FSA Tempo Adventure too, which also uses its own weirdo BCD), and the chainrings really do have lifespan issues. I think there will probably be an aftermarket solution sooner or later. Oct 14, 2021 at 19:10
  • @TomVine I'm not sure when these came out, but it looks like FSA makes a couple 1x chainrings: fsaproshop.com/products/agx-1x-chainring. But the teeth on it look pretty narrow as if they're already worn out.
    – bitmaker
    Jun 8, 2022 at 16:11
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    FSA 120mm chainrings AREN'T an asymmetric bolt circle.
    – PIER
    Dec 1, 2022 at 23:47
  • FSA has made up a couple weirdo chainring standards in recent years ... "recent years"? FSA also used 24.07 mm spindles so you couldn't use cheaper, better, and longer-lasting Shimano bottom brackets and were forced to use FSA's crappy, more expensive, and quicker-to-fail ones. I now avoid FSA like the plague. Dec 2, 2022 at 19:07

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