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I have found that bike shops will happily replace cassettes and chains. In contrast, even if a chainset is showing wear, they will be unlikely to change it. My brother just went to get his bike serviced and I noticed that his chainset is shark toothed and they only replaced the chain and cassette.

Has anyone else noticed this? If so, do you think there is there any reason for this?

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    one can only speculate. my speculation: the shop didn't want to be seen as upselling/over charging a customer that they guessed didn't take much care of the bike in the first place
    – Paul H
    Apr 2, 2021 at 19:25
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    Aside - your Brother might consider learning to do this stuff himself. Its a lot cheaper, you learn about your gear, and get a sense of satisfaction too. Chain and cassette are a doddle to change, and chainrings are not much harder. Cranksets would be more work but a like-for-like swap would limit the number of things to go wrong/mismatch.
    – Criggie ♦
    Apr 2, 2021 at 23:23

3 Answers 3

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The chainrings last a long time but are expensive, and a lot of cyclists are surprisingly tight when it comes to servicing.

Worn rings should be replaced when necessary though, otherwise the shop is throwing away good reputation and good income.

The teeth on many modern rings are often quite pointy and shaped, making identifying wear that much less straightforward.

I'm sure there's no one true answer.

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  • Yeah that's true, I'd imagine most people would think they're being ripped off unless they explicitly state they want a chainset changing.I may be wrong about it being sharp toothed, I'm hardly the most observant when it comes to these things. Though the largest and middle chainring do look worn and he said he uses these gears more than the smaller chainring. I guess I was thinking in terms of it might take longer for them to change a chainset or they might have to order parts in.
    – Jack Hudson
    Apr 2, 2021 at 19:35
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    My thoughts are there are two types of bikes which wear out chain rings, The big miles per week, dedicated riders the shop replaces when needed without hesitation, and the 'beater' (bikes could be the same person), where, due cost, chainring replacement requires a careful conversation, ideally started by the customer.
    – mattnz
    Apr 2, 2021 at 19:41
  • Regarding effort, chainring/chainset replacement is one of the faster/easier jobs when replacing like for like. Aftermarket or different spec components are another story.
    – Noise
    Apr 2, 2021 at 20:41
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    @JoeK you have to have "like for like" in stock though. My main LBS hasn't sold a mountain bike with a front derailleur in several years. If someone walked in with a 46-36-26 triple to be replaced, you'd have to wait a few days
    – Paul H
    Apr 2, 2021 at 21:05
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    @mattnz I'm one of those, and if a beater bike needs much more than a chain or BB, I buy a replacement beater bike 2nd hand, for a similar cost to a chainset (purchase, no labour as I do it myself). That's partly because my beater is kept near work and it's a major logistical hassle to get it anywhere I can do big jobs.
    – Chris H
    Apr 3, 2021 at 8:33
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In my experience, a chain or cassette cost half what a chainring costs, and an integrated chainset costs much more.

A bike shop's charges vary, but labour is a significant part of the cost. If they spend an hour on a task, that time is charged, and its well above the hourly wage of the mechanic doing the task.

A complex time consuming task plus the part costs do add up, and if the customer chooses not to pay then the bike shop is left with the repaired old bike to sell. This is a lot more work and therefore less profit than selling a new bike.

Example - why would customer pay $500 for a repair when a new MTB is $500 on the LBS floor ? (or a complete new BSO is $200)

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    One problem compounding this is that rivetted chainsets are common on cheap bikes, so you can't just replace the worn ring(s), but the cranks as well. With labour that's a decent fraction of the bike's cost.
    – Chris H
    Apr 3, 2021 at 8:30
  • So, the $500 is split as 250 for the chainring, $125 for cassette and $125 for chain... 12-speed cassettes are expensive, but where can you get that kind of chainrings and chains?
    – ojs
    Apr 5, 2021 at 12:53
  • @ojsIf the repair was $500 then ballpark half of it as labour.
    – Criggie ♦
    Apr 5, 2021 at 19:31
  • @Chris H the riveted chainsets are actually cheap cheap. The whole set costs half what a quality 50t chainring costs alone.
    – Noise
    Apr 16, 2021 at 7:35
  • @JoeK, there are also plenty of quite cheap bolted sets. I've got Sora on the tourer and Alivio on the MTB, both 9 speed, and I've changed individual rings on both. An Altus or Tourney 7/8-speed riveted set costs about as much as a 2nd hand beater bike. Of course there are slightly cheaper sets but the Shimano ones are most likely to be in stock
    – Chris H
    Apr 16, 2021 at 7:56
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The reason is simple, it's due to the properties of the chain drive system.

  • A worn driving sprocket engages to both worn and new chains.

  • A new driving sprocket engages to only new chains.

So, by having a worn driving sprocket, your bicycle is superior to one that has a new driving sprocket. You aren't limited to using only new chains, you can use worn chains too!

For the driven sprockets, the rules are as follows:

  • A worn driven sprocket engages to only worn chains.

  • A new driven sprocket engages to both worn and new chains.

So, in the back you want to have a sprocket that isn't too worn. If it's worn, you can't switch to a new chain without switching to a new driven sprocket as well.

Because sprocket wear accelerates quickly with a worn chain, you'll want to replace the chain regularly. If you replace it early enough, you might get several chains worth of wear from your driven sprockets. But eventually you need to change the driven sprockets too because they refuse to work with a new chain.

In contrast, good chainrings last practically forever. You might want to rotate them occasionally to get even better lifetime because they wear according to the pedaling forces that are uneven. Rotation is ideally 90 degrees which is only possible with regular 4-bolt attachments. With 5-bolt attachments, you can only approximate, and with irregular 4-bolt attachments (like the one Shimano is unfortunately using) you can't rotate.

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    You might want to source your claims. I have doubts they are true. That's why people downvoted I guess.
    – Nobody
    Apr 3, 2021 at 9:49
  • In addition, even if true, it is ahardly a reason for the bike shop service choises.
    – Vladimir F Героям слава
    Apr 3, 2021 at 9:51

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