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I'm looking to replace one of my three chainrings, and I'm having a hard time finding something that matches my bcd/bolt-pattern/tooth-count. I have found a few options, but they say they are for 10- or 11-speed drivetrains. I have a 9-speed drivetrain. Will the "speed" of a given chainring make much difference?

(I'm using a 3x9 drivetrain)

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Will the "speed" of a single chainring make much difference?

Chains typically have approximately the same internal width (with very small differences so not exactly the same). The external width of a chain however varies. So higher speed chainrings for multi-chainring systems typically have the teeth slightly offset so that the chain can't "skate" over the inner ring teeth when first shifting all the way up in the rear and only then shifting to the small ring in the front. It isn't reasonable to shift that way, so in practice you can have a mismatch of about one generation in the "speedness" of chainrings. So 9-speed ring on a 10-speed system or 10-speed ring on a 9-speed system works fine.

Actually sprocket thickness for 10 and 11 speed systems is the same, 1.6 mm. For 9 speed you would use 1.78 mm and for 8 speed and smaller than that you would use 1.85 mm. So the mismatch of 0.18 mm is very minimal and shouldn't prevent operation. In any case, the mismatch is in the correct direction (too loose as opposed to too tight) so it would be very unlikely for it to not work.

Since the difference between 10 speed and 9 speed is one generation only, it's very likely to work. The absolute worst thing that can happen is that if you use some chainring other than the biggest one and smallest rear sprocket, at the same time, the wider 9-speed chain could rub on the bigger chainring. It isn't reasonable to cross-chain in that way.

So use your gears in a reasonable manner and it should work.

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  • Do note that the OP specified a single chainring, so cross chaining is part of the package.
    – Weiwen Ng
    Mar 30 at 16:12
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    @WeiwenNg I initially read it as a "single chainring setup", but then I realized "single chainring in a 3x9 setup" so I modified my answer before posting it. I think the OP means 3x9 setup, not a 1x9 setup. Also, in a 1x9 setup the chain can't rub on the bigger chainring when cross-chaining since there's no bigger chainring!
    – juhist
    Mar 30 at 16:14
  • I agree with Juhist’s interpretation.
    – MaplePanda
    Mar 30 at 16:29
  • @juhist Correct: I am replacing 1 of the 3 chainrings (outer chainring, specifically) in a 3x9 setup. Mar 30 at 16:59
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    It looks like I am the one who read too fast.
    – Weiwen Ng
    Mar 30 at 17:20
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Your chainring has to match the bcd/bolt-pattern or it just won't fit.

No, it doesn't have to match your chain speed. I run an 11s Shimano crankset on a 10s chain but then I couldn't run a 9s crankset on a 10s chain. But I don't think you could swap a different speed chain ring onto your cranks because I don't think it would fit.

Yes, you can change tooth count, say from a 34t to a 36t. You may even get better shifting by decreasing the difference between rings like going from 50-34 to 50-36. But you may be problems increasing the difference like going from 53-39 to 53-34. You'll also have to re-consider your chain length and whether rear derailleur capacity is large enough: (large - small ring) + (large - small cog).

When you're done with it all, you will have to check your derailleurs alignment and shifting if you make any of these changes. And check your chain length.

I think your best option is to find a slightly different tooth count ring in your speed and BCD.

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  • Why would a chainring not fit on crank specified for different speeds?
    – ojs
    Mar 31 at 8:32

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