I noticed that my bike's chain is rubbing the chain stay when I use the lower gears.

The bike is new; I'm wondering what the problem is.

chain touches upper side of chainstay

  • Out of curiosity, what make is this, and where did you acquire that bike? Commented Nov 13, 2022 at 21:14
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    The chain's too long. Commented Nov 13, 2022 at 22:43
  • This is an NS bike. I bought it on Chain reaction Commented Nov 14, 2022 at 3:07
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    If you try to push the derailleur cage up by hand, what happens? How does it shift in the other gears? Also, check that the der is mounted correctly--there will be a tab on the derailleur that needs to butt up against the tab on the frame's hanger.
    – MaplePanda
    Commented Nov 14, 2022 at 3:37
  • Surprised to hear that ChainReaction did such a sloppy job. They are usually good. Even if you fix it yourslef I recommend you send them a feedback message to stop this happening in the future. Commented Nov 14, 2022 at 9:41

1 Answer 1


Proper way of dealing with this

If the bike is new, take it back to the shop that sold it to you and ask them to fix it.

My thoughts on what is actually wrong with the bike

On the picture it looks like your derailleur is fully collapsed and the chain is sagging. This looks like an incorrectly sized chain (too long). A shorter chain would not allow the derailleur to fully collapse and it would keep the chain under tension, preventing it from sagging and touching the chainstay. However this is only one part of the problem. Don't hurry to go and shorten your chain just yet.

Before you shorten the chain, check what is the situation on the other end of the cassette. Check that the chain is actually long enough to be shortened without losing lower gears. If unsure, post an image of the chain shifted into the largest cog on your cassette. This is important(!). If you just shorten the chain making it too short and then attempt to shift into the largest cog, you are likely to destroy your derailleur.

If your chain appears to be correctly sized in the largest cog, but still sags in the smallest cog, it may be that your bike is equipped with the wrong derailleur (cage too short).

Additional thoughts

Looks like you have a Shimano Deore 12-speed derailleur. It looks like RD-M6100-SGS. On Shimano website I can see that that it has 51T max capacity. The cassette you have looks like Sunrace 51T cassette, so in theory should work with this derailleur if the chain is sized correctly.

Further reading

  • 1
    Thanks for your explanation, after checking your suggestions, everything points to a larger chain. I checked the components for compatibility and you targeted each of them. I also get a lot of rubbing behind the chain ring (in the photo I put a lot of gorilla tape), doing some research, this is called "chain suck" and one of the reasons for having that is a larger chain. Commented Nov 14, 2022 at 20:11

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