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My chain was badly worn. 1.0+ % wear. There is no visible shark toothing or extreme spacing on chainrings. Is there a chance I can get away with not replacing the chainrings, or does the amount of chain wear automatically necessitate that I replace them?

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    You can get away - but you will have to buy new everything later, not just the chain. Or you will have to buy only used chains... – Vladimir F May 11 at 18:29
  • My rule of thumb: Change the cassette with each chain and the rings with each other chain. – Carel May 11 at 19:16
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    @Carel: How long do you use a chain? Imho a cassette should last >10Mm. For me that’s about 4 chains. – Michael May 11 at 19:40
  • @Michael: Looking at my gear listings on strava they tell me that chains (11s) last between 2500 and 3000km, Shim, SRAM or KMC. – Carel May 12 at 12:32
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    @Carel: Are you seriously throwing your cassette away after only 2500km? – Michael May 12 at 12:44
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I think that one rule of thumb I saw asserted that if you replaced promptly, you could get 2-3 cassettes per chain, and 2-3 sets of chainrings per cassette. I'm not able to provide a concrete source for this right now. However, the fact is that chainrings do wear more slowly than cassettes because they have more teeth.

I think very likely that your cassette needs replacement, and I would do that preemptively. I would not replace your chainrings right now, unless they have had several prior chains that also got to a high level of wear. For smaller chainrings, I would probably lean slightly more towards preemptive replacement.

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    A cassette lasts me >10Mm. Chains usually last me over 2Mm. So I use about 4 chains per cassette. I don’t do any special cleaning, just regular lubing. 10 and 11 speed Shimano transmissions. – Michael May 11 at 19:42
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    I agree with your replacement interval, but you phrased it in a odd way. You should replace the chain 2-3 times before replacing the cassette, and you should replace the cassette 2-3 times before replacing the rings. Right? – sam May 12 at 0:42
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When should I replace my....

Chain? When the chain checker says your chain is over 0.5% worn.

Cassettes? When you start experiencing "skipping" in your most popular sprockets.

Chain rings? When you see very obvious "shark teeth" on your chain ring teeth.

Yes, it is true that there are more reasons why you should replace these components, but these are the "most common" in my experience. And remember: a worn chain will wear down your chain rings and cassette, but worn chain rings and cassettes will not wear down a chain.

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  • Why should you change chainrings when seeing shark teeth? My touring bike has shark teeth in its big ring, the ring I use most. It works just fine, no issues there. According to the "shark teeth" rule, I should have already replaced it. – juhist May 12 at 4:35
  • @juhist because the worn out chainring will degrade your chain and consequently your cassette faster than it would otherwise. – Christian Lindig May 13 at 7:37
  • Is there a source for “worn chain rings and cassettes will not wear down a chain”? I’m not necessarily disagreeing, but some of the other comments in this thread do contradict that assertion. – high-gear May 14 at 5:43
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Two main schools of thought exist.

  1. New rings every X cassette replacements, and new cassette every Y chain replacements. This required consistent records kept up to date correctly. Nowdays this is much easier with software like Strava, provided you set up the parts on your bike.
    This is the more-expensive method in the short term, because you are replacing parts while they still have some wear left in them. This leads to better performance overall, so would be the racer's preference.

  2. Ride it and change parts when the function stops being reliable. This is more common on bikes used as transport rather than exercise or racing.
    Also if I have a used bike with an unknown mileage on its parts, then I might take the extreme course of riding till it fails completely, and then replace all the transmission parts (cassette/chain/jockey wheels, maybe chainring if needed, along with inner/outer cables, brake pads, bartape/grips)
    This tends to cost larger amounts but less-often.

Overall, either plan still costs less than driving a car the same distance.

Personally, I rarely change chainrings because they wear much slower having so many more teeth engaged. I tend to change cassette along with a new chain.

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No! No! No! A thousand times no!

A worn chainring engages to a new chain (and a worn chain too).

A well-worn chain does not engage to a new chainring. So in fact the converse is true: you don't want to replace chainrings when replacing the chain, but you do want to replace the chain when replacing a chainring.

I have a crankset with visible shark toothing in the chainrings even though the chain wore to just over 0.5%, never reaching anywhere near 1.0%. The chainrings work just fine with a new chain.

There are two reasons you might want to replace chainrings:

  • Wear. Good big (50 tooth) chainrings made from highest quality 7075T6 or 7075T651 aluminum can last perhaps nearly as many kilometers as a typical car engine. There used to be a picture by Jobst Brand of a chainring that had seen just this mileage. The teeth were very worn but the chainring still barely worked. The chainring was rotated 72 degrees several times in its lifetime (it was a 5-bolt chainring and not a 4-bolt that would support 90 degree rotation) to even out wear. Unfortunately, the picture is no longer online. However, this demonstrates that good big chainrings do indeed last a long amount of time. A single 1.0% chainwear incident is not a reason to replace chainrings.

  • Chainsuck. In some cases, small chainring used in bicycles with long cage derailleurs (mountain bikes and hybrid bikes) can experience chainsuck where the chain does not disengage from the chainring as it moves towards the rear derailleur. The only solution to this phenomenon is replacing the chainrings. On road bikes where 99% of the time the big ring (50-53 teeth) is used and the derailleur cage length is short, this never happens.

However, before you claim that your chain is 1.0% worn consider the quality of the tool you use for measurement. Today, the only reliable chainwear tools are Shimano TL-CN40, TL-CN41 and TL-CN42 which are simple go/no-go tools telling whether the chain is worn more or less than the limit (probably 0.5%). See here for details. I know of no tool that would tell 1.0% wear that would be reliable, apart from an inch ruler longer than 12 inches (a foot).

So if you are not measuring your chain with an inch ruler but rather using a tool that tells 1.0% wear, your measurement is probably crap. Discard the tool and buy a Shimano TL-CN42 instead.

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    Most recent shaped big rings fit the cranks in one position only and even the flat ones have a chain catching pin to be placed at the DS crank. The small rings have a position indicator to enable a correct functioning of the shifting ramps. – Carel May 11 at 19:22
  • Why do you think only the Shimano chain wear gauges are reliable? At least BBB makes a cheap and good tool as well: images.thebicyclelounge.co.uk/product-images/1000-1000/… – Michael May 11 at 19:33
  • @Michael If you believe the pardo.net link, the BBB tool measures the wrong thing. – ojs May 11 at 20:12
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    I think the Pardo link is probably correct about where we should be measuring wear, but it said that almost all tools were inaccurate in 2009/10, i.e. over 10 years ago. By now, other manufacturers have put out better tools. cyclingtips.com/2019/08/bicycle-chain-wear-and-checking-for-it – Weiwen Ng May 11 at 22:53
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Take round file and do each tooth it's a dirty fix but works, the file must be same size as the tooth maybe slightly smaller just don't make the teeth larger as this will stretch the chain, the idea is to make them deeper.

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  • This can't possibly work, since if you take the same amount off each tooth they'll be the same distance apart as if you hadn't done anything. And the lengthened chain still won't mesh properly with them. – DavidW May 13 at 22:04

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