My partner has got a brand new bike and while pedalling under load it makes a loud "clunk" noise, as if changing gears but without a corresponding gear shift. After some investigation I found that when this happens, the front sprocket is "catching" on the chain, pulling it up, and then releasing it a few links later. The rear derailleur then springs back and the chain becomes very loose for a short moment. The clanking noise, then, is the chain hitting the frame. Here's a diagram to help explain:

diagram of the chainsuck

I'm a cycling novice, but I learned that this is fairly similar to "chainsuck", though with all examples of chainsuck I could find, the sprocket never releases the chain and pedalling is forced to stop as the chain is dragged into itself. This doesn't happen here: It always releases just a few links too late.

Is this chainsuck? How do I fix it?

Most common causes of chainsuck seem to be due to aged chains, aged sprockets, or both, but this is a new bike. I've also made sure that the chain is adequately lubricated. The bike also clunks fairly dramatically while changing gears, so I wonder if perhaps the chain might be too long? The chain feels fairly loose, but I'm not sure how tight they are meant to be.

This is what the bike looks like: enter image description here

  • Regarding chain tension: When you are in the smallest rear sprocket, is there still tension in the chain or is there some sag? But I agree with Nathan, this simply shouldn’t happen with new components. Have you tried adjusting the rear derailleur to improve shifting performance?
    – Michael
    Commented Jan 1, 2022 at 8:12

1 Answer 1


Since it's new the ideal thing would be make whoever you bought it from fix it.

When this problem happens on a bike where wear or muck isn't a factor, usually what's going on is there's one particular area on the offending chainring that's been bent, distorted, gouged up, and/or poorly formed, and that's where the chain is catching. In many cases that area can be cleaned up to lessen or eliminate the problem, but it may not be a fix that lasts depending on what caused it initially. If a tooth is bent, for example, straightening it (an adjustable wrench is ideal) could solve the problem completely if what started it in the first place was the ring getting bonked against something or just badly made.

It would be weird to see, but check to make sure the chainring isn't actually for 1/8" chain. It should mesh easily with the inner chain links, not like it's being stuffed in and barely fitting, or borderline.

  • 5
    A stuck link may also be the culprit.
    – Carel
    Commented Jan 1, 2022 at 8:11
  • Thanks, I'll investigate these!
    – Matthew
    Commented Jan 1, 2022 at 23:57

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