• How to use this section. To the thread starter: Once you are satisfied with the answer that youve been given, click the Trophy on the left hand side of the message. This will rate this answer as the 'Best Answer' and will change the question status from 'Unanswerd' to 'Answered'. All members can also upvote an answer with the 'Up' arrow, this will help identify the best answer.

New chain flapping making noise

J

james4555

New Member
Joined
Jul 2, 2025
Messages
15
Reaction score
4
Location
Sheffield
Just got my bike back from the lbs and the chain is flapping near the chainring.

Video of it happening below

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.
youtube.com youtube.com

Had a new chain and cassette fitted.
 
Sort by date Sort by votes
⚡ EMTB Pro Go Pro — exclusive discounts & ad-free Peaty's 25% off & more · Ad-free browsing · Pro badge See the deals →
It's either he has fitted the wrong chain, which is a narrower chain, like a 12 speed chain. Thus it's grabbing the chainring teeth too tight. Or the chainring is too small. It's not releasing the chain. You cannot have a big tooth, small tooth chainring on a chainring that small. It can't release the chain cleanly.
 
Upvote 0 Downvote
Astro66 said:
It's either he has fitted the wrong chain, which is a narrower chain, like a 12 speed chain. Thus it's grabbing the chainring teeth too tight. Or the chainring is too small. It's not releasing the chain. You cannot have a big tooth, small tooth chainring on a chainring that small. It can't release the chain cleanly.
Click to expand...
The bike is a Cube Reaction Hybrid CUBE PRODUCT ARCHIVE | Reaction Hybrid SL 500 black edition 2018

20250704_160933.jpg

think it's the same chain as the old one KMC X11 is there different versions of that chain
 
Upvote 0 Downvote
Parts look correct. But the chain is not releasing off the chainring cleanly.

I don't know. Does the derailleur have a clutch ? Is it turned on ?
 
Upvote 0 Downvote
james4555 said:
Thought so I did ask them to put a new one on but he said it was ok. The rear mech is flapping as well do you think changing that would also help.
Click to expand...
If you've changed the chain and cassette it can only be the chainring, probably the teeth are worn and won't release the chain cleanly

see attached photo from another post

msedge_onoUyRoPuH.png
 
Upvote 0 Downvote
james4555 said:
thanks ill give it a try
Click to expand...
I really can’t tell, or don’t know, if your chainring has narrow/wide cogs. If it does then the narrow chain link may be on a wide chainring cog. Moving, or jumping the link one position over the chaining may solve the issue. (It’s easy to happen when a new chaining or chain is installed. Your chain may behave as shown in your video. (Like chain suck)(A narrow link is trying to fit over a wide chainring cog).

Maybe that’ll help 🤷🏼‍♂️
 
Upvote 1 Downvote
Stihldog said:
I really can’t tell, or don’t know, if your chainring has narrow/wide cogs. If it does then the narrow chain link may be on a wide chainring cog. Moving, or jumping the link one position over the chaining may solve the issue. (It’s easy to happen when a new chaining or chain is installed. Your chain may behave as shown in your video. (Like chain suck)(A narrow link is trying to fit over a wide chainring cog).

Maybe that’ll help 🤷🏼‍♂️
Click to expand...
Just done a measure of the chainring with some callipers
20250705_201510.jpg
it's a 15 teeth chainring and it's 65mm wide. The teeth are 4mm wide at the top and the gap between each teeth is 10mm at the top.

The spacing between the rollers of the chain is 5mm and 5.3mm and the width is 4mm and 2mm20250705_202018.jpg
Hope that helps.
 
Last edited:
Upvote 0 Downvote
Amber Valley Guy said:
I'd imagine a 15t chainring (15t, that's tiny) wouldn't last long before being totally shagged out, and it's going to eat chains for breakfast being such a tight radius.
Click to expand...
What chainring do you recommend to use that's compatible with the KMC X11 chain ? i use the bike for commuting to work and a few TPT trails around South Yorkshire.
 
Upvote 0 Downvote
james4555 said:
What chainring do you recommend to use that's compatible with the KMC X11 chain ? i use the bike for commuting to work and a few TPT trails around South Yorkshire.
Click to expand...

I don't know you bikes motor, if that chainring is standard fitment I'd guess it was designed that way? Did it ride OK before the new chain and cassette? If so replace the chainring. Also does the derailleur have noticeable tension when pulled forward towards the front wheel (I don't think yours has a clutch)? If not that could also be the problem. It (the derailleur) should have strong spring tension to take up the slack when in the smallest rear sprockets on the cassette.
 
Upvote 0 Downvote
Amber Valley Guy said:
I'd imagine a 15t chainring (15t, that's tiny) wouldn't last long before being totally shagged out, and it's going to eat chains for breakfast being such a tight radius.
Click to expand...
My old bike with a Gen 3 Bosch CX motor also had a 15t chainring I sold it after 4 years use and over 4k Km still with the original chain, chainring and cassette never had any problems with it! I would imagine modern chains are more than able to handle such a tight radius even those even tighter top gear 11t ones on the cassette!🤨
 
Upvote 0 Downvote
Joecrow said:
My old bike with a Gen 3 Bosch CX motor also had a 15t chainring I sold it after 4 years use and over 4k Km still with the original chain, chainring and cassette never had any problems with it! I would imagine modern chains are more than able to handle such a tight radius even those even tighter top gear 11t ones on the cassette!🤨
Click to expand...

Are you taking the piss?
 
Upvote 0 Downvote
james4555 said:
Just done a measure of the chainring with some callipers
View attachment 163697
it's a 15 teeth chainring and it's 65mm wide. The teeth are 4mm wide at the top and the gap between each teeth is 10mm at the top.

The spacing between the rollers of the chain is 5mm and 5.3mm and the width is 4mm and 2mmView attachment 163698
Hope that helps.
Click to expand...
I can see what I think is the problem. Your chainwheel teeth are not of the narrow-wide variety, and they look all wide. Which means you are getting chain sucking to the chainwheel on every second link.

I just measured my narrow-wide chainring. The chainring teeth thickness at the bottom of the teeth is 1.9mm at narrow teeth, and 3.6mm at the wide. It looks like all your chainwheel teeth are about 3.5mm thick.

The only way to explain this is if the LBS bought a new chainring, but it was the wrong type. Or the original chain was wider.

Anyway. If you have a vernier. See if you can measure the chainwheel thickness at the bottom of each teeth. If all the teeth are about 3.5mm. It's a problem.
 
Upvote 0 Downvote
Amber Valley Guy said:
Are you taking the piss?
Click to expand...
Maybe a little, sorry, but the 15t chainring with a 11t to 42t cassette was a typical setup on the old 75nm Bosch CX motors so suggesting it would be the cause of very rapid chain wear is certainly not my experience and seemed worthy of some doubt casting!
Both my posts here are off subject anyway and little help for the OP, hope the other posts help get the problem fixed.
 
Upvote 0 Downvote
Astro66 said:
I can see what I think is the problem. Your chainwheel teeth are not of the narrow-wide variety, and they look all wide. Which means you are getting chain sucking to the chainwheel on every second link.

I just measured my narrow-wide chainring. The chainring teeth thickness at the bottom of the teeth is 1.9mm at narrow teeth, and 3.6mm at the wide. It looks like all your chainwheel teeth are about 3.5mm thick.

The only way to explain this is if the LBS bought a new chainring, but it was the wrong type. Or the original chain was wider.

Anyway. If you have a vernier. See if you can measure the chainwheel thickness at the bottom of each teeth. If all the teeth are about 3.5mm. It's a problem.
Click to expand...
Done a measure and the thickness on the chainring of all the teeth at the bottom is 2mm. The previous chain was a Shimano one. Would they have installed a chainring that would only work with Shimano and not a KMC chain.
 
Last edited:
Upvote 0 Downvote
This might not be any help whatsoever, but there's probably more fake KMC chains in the world than genuine ones. Even the plastic box packaging looks exactly the same. If somethings wrong, take it back to the lbs who you paid to sort it out.
 
Upvote 0 Downvote
Amber Valley Guy said:
This might not be any help whatsoever, but there's probably more fake KMC chains in the world than genuine ones. Even the plastic box packaging looks exactly the same. If somethings wrong, take it back to the lbs who you paid to sort it out.
Click to expand...
Have done twice and both times they claim to have sorted it even said they test rode it but still happening. Booked it into another lbs i've used in the past see what they think fresh pair of eyes. Will point out what's been suggested here learnt a lot and thanks for all the help and suggestions.
 
Upvote 0 Downvote
Astro66 said:
Then maybe try a 11S Shimano Chain. It would only be about 20 pound.

That does seem correct for a Narrow only chainring.
Click to expand...
Tried a brand new shimano chain today still the same. Will try a new derailleur next and also a new chainring on the way so hopefully one will work.
 
Upvote 0 Downvote
I'm beginning to think there is something else going on. Before you start replacing all the parts, as this can get expensive, and may not solve it. I would get a good bike mechanic to look at it.
 
Upvote 0 Downvote
You must log in or register to reply here.
Keep reading
    Browse all

    Similar Threads

    Community Stats

    Since 2018
    669K
    Messages
    40,921
    Members
    Join 30,000+ Riders, it's free!
    Back
    Top