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I have a MTB with a Shimano 12 speed 1x setup (M7100/8100 XT/SLX components mixed).

My chain is worn, as indicated by my tool, so I need to replace it, along with the casette.

But: should I replace my chainring too?

Since this is a 1x narrow-wide setup, there is no shifting performance degradation to worry about. But: a worn chainring can wear a new chain fast....

There is no visible cue that there is anything wrong with the chainring.

Btw. the drivetrain still works, shifts well, so maybe the chainring is not quite beyond its life yet?

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  • Is the chain at 0.5% wear or is it at 0.75%?
    – Weiwen Ng
    Mar 8 at 15:28
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    Why the cassette - how many chains have you been though? Should be OK to just replace the chain unless you have already been though a few.
    – mattnz
    Mar 8 at 18:44
  • @WeiwenNg my tool has only one way to measure chain wear, and it does not say what percentage :(
    – haspok
    Apr 10 at 10:10
  • FYI I ended up replacing the casette with the chain, but not the chainring. I did not see much wear on it, and it seems to be working fine. But I also bought a spare chainring, just in case...
    – haspok
    Apr 10 at 10:12

5 Answers 5

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On a 1x bike, when the chainring is not overtly worn, a large factor that drives this question is the cost relationship between the cassette and chainring.

There are plenty of bikes out there now where the cassette costs some large (relative to the past) multiple of the ring, like 6 times. Since exposing a new chain to a worn ring accelerates wear on the chain, which in turn accelerates wear on the cassette, the question (presuming a money cassette) is all about how to work the economics of the situation.

The tricky thing in practice with this question on 1x rings is that they're teeny and you're on the same one all the time so they're that much more wear-prone, but the newfangled tooth profiles are also resistant to some of the traditional chainring wear symptoms, like slipping under load.

Presuming a bike that will be around a while, a smart approach is buy the replacement chainring you'll eventually need anyway, and then use the visual comparison with the old one to guide your decision. Look at the difference in tooth profile. Is material worn off the front of the old chainring teeth? If you can see that there's really any observable change in the tooth profile and it's a typical modern 12-speed bike with a cassette that costs 5 times as much as the ring, sure replace it, the savings is probably there.

The world is currently lacking a unified rule of thumb about this question on 1x bikes, but it would not be surprising if eventually the answer just became yes, replace it. A huge piece of that is 28t and 30t etc rings wear quickly anyway, but of course with that there's also the qualifier that there's often a world of difference between brands with really good control over things like metallurgy and heat treatment with their chainrings (Shimano) and companies who chronically couldn't care less (FSA).

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My chain is worn, as indicated by my tool, so I need to replace it, along with the casette.

Not necessarily. If you don't let the chain wear too much, you can easily get 2-3 chains per cassette.

But: should I replace my chainring too?

Almost certainly no, unless the chain is so worn it's at a danger of snapping anyway (in which case it may have worn the tooth shapes too much).

Chainrings last practically forever. It's not unknown of to get as many kilometers from a chainring as you can get from a car engine.

But: a worn chainring can wear a new chain fast....

Why are you imagining so?

A worn chainring will not cause any accelerated chain wear. On the contrary, a worn chain may cause cassettes and chainrings to wear but not vice versa.

For the chain and related components, the rule is as follows: if you replace a component with a new one, anything behind it may need changing, but anything in front of it works.

Examples:

  • You replace the cassette only. An old chain will work.
  • You replace a chain. You may (or may not) need to replace the cassette
  • You replace a chain. An old chainring will work.
  • You replace a chainring. You may (or may not) need to replace the chain, which means you may (or may not) need to replace the cassette
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    2x chainrings should last a long time, I agree. I am not 100% sure about 1x rings, and i think they may need replacing more than 2x. Mainly due to being smaller plus the only ring, secondarily due to cross chaining in the lowest gears.
    – Weiwen Ng
    Mar 8 at 19:06
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0Generally with the % wear tools, I advise to replace "chain only" at less than 0.75% unless cassette is worn.

Replace cassette, ring and chain if wear is over 1%. If your 1x chainwheel uses a small tooth count (28, 30, etc) it may wear faster but the larger sizes last a long time if not abused (40t+). If the feel is a bit rough with the new chain, replace the chainring too but there's no need to do it as a matter of course. The steel chain is significantly harder than the soft alu chainring and will not be damaged especially if the drivetrain feels smooth.

If you replace a chain at 0.5% wear, you are throwing money away unless this is your race bike equipped with Dura Ace/ Red / Super Record and you are competing.

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    You are stating the correct wear guides for 10S and earlier chains. Newer chains do need to be replaced at 0.5% for best results - potentially penny wise and pound foolish to insist on replacing at .75% cyclingtips.com/2019/08/bicycle-chain-wear-and-checking-for-it
    – Weiwen Ng
    Mar 8 at 19:08
  • @WeiwenNg I run 11 and 12sp systems too, and have serviced these many years. I don't find a difference in wear character but you are free to disagree. My reputation locally is not relevant here.
    – Noise
    Mar 8 at 20:13
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I'd not change the chainring.

You should test its wear by fitting the new chain, press the chain into the chainring at the top or 12oclock position, and see if you can pull the chain away from the chainring at the front/3oclock to the bottom/6oclock.
Compare that with your old stretched chain and see the difference in fit.

Chainrings last a very long time compared to everything else in the drivetrain, mostly due to their much higher tooth/chain engagement.

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Comes down to price. 12 Speed chainrings are only about $US25-$100, chains are similar, cassettes are $100-$550.

For me, everything I did would be around extending cassette life - pedantic, regular chain replacement with a new chainring at the very first sign of wear. If putting on a new $US500 cassette, why risk shortening life of the cassette over chainring worth less the 1/5 of the price?

Replace chain rings rarely thinking comes from the days when there were multiple chainrings and cost of two of three chainrings relative to cassettes was a lot more than it is today. One chainring now does all the work, therefore more likely to be worn, and cassettes now very expensive compared to that one chain ring, makes treating chainrings almost as disposable as chains sensible.

If replacing the cassette, a new chain and chainring should be considered mandatory.

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