Chainring teeth?

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James Up Hill
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Chainring teeth?

Post by James Up Hill »

Chain snapped today (on my Triban 500RC that is 12 months old and can't have done much more than 1,000-1500 miles in that time - for all that it's central London commuting).

Chap in shop said I needed a new chain as it had stretched, so I fitted a new one; it is now running beautifully and has all been carefully adjusted. But I looked at the front chainring (Shimano Sora 9s 50-34 MP) and the teeth look like this. Is this right? It looks to have broken teeth, and shark's teeth. But equally I find elsewhere on the internet a suggestion that the teeth aren't all the same, to 'aid shifting'.

I'm 70kg, I don't hang about, but I'm kind to my bike and I'm not a nutter cyclist! And I'm certainly not aware of having done anything to break off a tooth.

Thoughts, please? Is this normal or do I need a new one?

Many thanks!
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fossala
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Re: Chainring teeth?

Post by fossala »

Chainring is fine, teeth are like that to help shifting as you say. Aren’t even close to being worn.
Pebble
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Re: Chainring teeth?

Post by Pebble »

the chain was "stretched" ? that is far from normal, what type of shop were you in?
jb
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Re: Chainring teeth?

Post by jb »

Normal for Shimano, they always look worn out from new.
Just keep riding.
Cheers
J Bro
Steve O'C
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Re: Chainring teeth?

Post by Steve O'C »

the chain was "stretched" ? that is far from normal, what type of shop were you in?
I think referring to chain wear as "stretch" is pretty common. If you measure chain wear with a tool like this then when the chain is worn the distance between the 2 rollers in contact with the points arrowed increases allowing the tool to slip down in to the chain making it appear that the chain has stretched.
Screenshot 2022-11-29 225110.png
Of course the side plates of the chain have not stretched what has worn are the pins and bushings in the chain which in turn increase the pitch (distance between the rollers) of the chain.

All this is common knowledge and my only point here is that I would not dismiss a shop or mechanic who referred to chain wear as "Stretch" as being incompetent.
Steve
Pebble
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Re: Chainring teeth?

Post by Pebble »

Steve O'C wrote: 29 Nov 2022, 11:12pm
All this is common knowledge and my only point here is that I would not dismiss a shop or mechanic who referred to chain wear as "Stretch" as being incompetent.
Steve
If it is coming from a bike mechanic then I would.
James Up Hill
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Re: Chainring teeth?

Post by James Up Hill »

Shame on me for not having looked at the chainring before! Thanks all.

Apologies to the chap in the shop if he had indeed described it as something other than stretched. Maybe my use of the words. No, of course chains don't actually stretch - or at least steels only creep at elevated temperatures and my chain doesn't glow red hot as I cycle... But the meaning is pretty clear, the chain does stretch, for all that the individual components do not and only because the bearings wear. :)
tim-b
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Re: Chainring teeth?

Post by tim-b »

Be wary of chain meausuring tools, some use inaccurate methods to measure the wear
~~~~¯\(ツ)/¯~~~~
alexnharvey
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Re: Chainring teeth?

Post by alexnharvey »

Pebble wrote: 30 Nov 2022, 12:15am
Steve O'C wrote: 29 Nov 2022, 11:12pm
All this is common knowledge and my only point here is that I would not dismiss a shop or mechanic who referred to chain wear as "Stretch" as being incompetent.
Steve
If it is coming from a bike mechanic then I would.
Your views on their competence notwithstanding, would you have understood what they meant?

If someone were to judge your competence in any domain on the basis of your use of a single commonly used term, how much weight would you give that assessment.
NickJP
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Re: Chainring teeth?

Post by NickJP »

tim-b wrote: 30 Nov 2022, 6:27amBe wary of chain meausuring tools, some use inaccurate methods to measure the wear
Ditto. Use a 12" engineers steel rule or vernier calipers to measure chain wear. Put the top run of the chain under tension and measure 24 links. When this measurement comes to ~12-1/16", I replace the chain. That's only 0.25% wear, but as chains are the cheapest part of the drivechain, it's better to replace the chain more frequently so that you can replace the chainrings and cassette less frequently. For road cycling, I get at least three chains (that's usually somewhere north of about 12000km use) across a cassette and chainrings before I need to think about replacing the latter.
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Chris Jeggo
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Re: Chainring teeth?

Post by Chris Jeggo »

NickJP wrote: 30 Nov 2022, 7:17am
tim-b wrote: 30 Nov 2022, 6:27amBe wary of chain meausuring tools, some use inaccurate methods to measure the wear
Ditto. Use a 12" engineers steel rule or vernier calipers to measure chain wear. Put the top run of the chain under tension and measure 24 links. When this measurement comes to ~12-1/16", I replace the chain. That's only 0.25% wear, but as chains are the cheapest part of the drivechain, it's better to replace the chain more frequently so that you can replace the chainrings and cassette less frequently. For road cycling, I get at least three chains (that's usually somewhere north of about 12000km use) across a cassette and chainrings before I need to think about replacing the latter.
1/16" in 12" is 1 part in 192, 0.52%. That's replace time for me, too.
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Cugel
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Re: Chainring teeth?

Post by Cugel »

NickJP wrote: 30 Nov 2022, 7:17am
tim-b wrote: 30 Nov 2022, 6:27amBe wary of chain meausuring tools, some use inaccurate methods to measure the wear
Ditto. Use a 12" engineers steel rule or vernier calipers to measure chain wear. Put the top run of the chain under tension and measure 24 links. When this measurement comes to ~12-1/16", I replace the chain. That's only 0.25% wear, but as chains are the cheapest part of the drivechain, it's better to replace the chain more frequently so that you can replace the chainrings and cassette less frequently. For road cycling, I get at least three chains (that's usually somewhere north of about 12000km use) across a cassette and chainrings before I need to think about replacing the latter.
You'd need to be a super-robot to hold a steel rule steadily enough and then view its reading accurately enough (without parallax errors) to make such a measurement. A good vernier will do the job, though - if it really is a good one. The cheap ones are useful for comparative measurements but can be inaccurate for absolute measurements, as needed with testing a chain for wear.

There are good quality chain "stretch" testing tools of the "drops through the links or doesn't" kind. Look for those that claim to have been CNC cut to a fine tolerance. They tend to cost more than the two quid versions stamped out of a plate.

Chain wear to swap-it status in 1200 - 1500 miles is a bit rapid. Is the OP cleaning and lubricating it often enough?

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
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Pebble
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Re: Chainring teeth?

Post by Pebble »

NickJP wrote: 30 Nov 2022, 7:17am
tim-b wrote: 30 Nov 2022, 6:27amBe wary of chain meausuring tools, some use inaccurate methods to measure the wear
Ditto. Use a 12" engineers steel rule or vernier calipers to measure chain wear. Put the top run of the chain under tension and measure 24 links. When this measurement comes to ~12-1/16", I replace the chain. That's only 0.25% wear, but as chains are the cheapest part of the drivechain, it's better to replace the chain more frequently so that you can replace the chainrings and cassette less frequently. For road cycling, I get at least three chains (that's usually somewhere north of about 12000km use) across a cassette and chainrings before I need to think about replacing the latter.
keep your used chains, and then give them a second life taking them from 0.25 to 0.75. If your cassette is heading for landfill then what does it matter.

On my last cassette I took six chains out to 0.6, then reused them from 0.6 to 1.2, then again from 1.2 to 2%. Got about 22,000 mile out of the cassette. They don't slip at 2.5% if the chains and the cogs have been worn down sympathetically to each other.

we need to think about the environment and not be too hasty in binning stuff off!

and the only way to measure chain wear with any accuracy is to remove and thoroughly clean the chain then measure its full length
jb
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Re: Chainring teeth?

Post by jb »

Whilst a chain may still be within acceptable limits as far as pin wear is concerned heavy use in gritty conditions may have worn the rollers. This in turn will allow the pins to drop further into the tooth recess and no longer be a match for the new pitch lower down.
If when the chain is sat on the chain ring the rollers stick up above the link plates I would say its Probably doing as much damage to the sprockets as a chain with worn link pins.
Cheers
J Bro
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Audax67
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Re: Chainring teeth?

Post by Audax67 »

FWIW, old and new chainrings:

Image

The cruddy one was on the bike for 11 years, whereof the bike was pretty well idle for 7 after I got my carbon butterfly. It has ~35,000 km on it. Both are Shimano 105 3x10. Interesting (or not) to note that design changed in the meantime.
Have we got time for another cuppa?
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