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Look at this. The spokes behind the cassette of my MTB are all scratched and bent. How might this have happened? The back of the cassette has no scratch at all.

worn out spokes

worn out spojes

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    that was caused by the chain getting stuck between spokes and cassette.
    – Burki
    Commented Aug 30, 2023 at 10:15
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    @Burki that is an answer, not a comment ;)
    – Rеnаud
    Commented Aug 30, 2023 at 10:24
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    A side note: I'd recommend checking that brake rotor. From what little we can see it might be close to or beyond it's limits.
    – Burki
    Commented Aug 30, 2023 at 10:36
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    From the discoloring, and from the appearance of a visible step in the brake surface. Typically, the thickness of a new brake disk is 2mm, and the minimum width is 1.5mm. So, signs of wear like what can be guessed here are at minimum a reason to get the calipers out
    – Burki
    Commented Aug 30, 2023 at 16:19
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    I posted a link to this old question of mine under the answer, but it's worth putting here too. It addresses the repair.
    – Chris H
    Commented Aug 30, 2023 at 19:20

2 Answers 2

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This kind of damage occurs when the chain gets stuck between the cassette and the spokes. It happened while riding, most likely, as indicated by the fact that the spokes are bent in the pull direction of the chain.

This kind of damage can be (mostly) avoided by making sure the limit screws of your rear derailleur are set correctly, and even more by adding a protective disc (a roundish piece of plastic typically clipped on the spokes, that would in turn take the impact should the chain get there again)

As @DoNuT mentions in the comments, the spokes are done for, at least from a fairly professional standpoint. I'd still like to point out that i have seen and ridden a number of bikes with similar damage to the spokes, that still lived for at least hundreds of kilometers, so i would not consider this damage a major security risk. Just make sure to check them regularly, and after the fist spoke snaps, don't wait any longer.

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    I guess it would be worth adding that the spokes are probably trash and ask for a replacement too, right? ;)
    – DoNuT
    Commented Aug 30, 2023 at 10:30
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    Indeed, I have also seen spokes with a similar damage to work for a long time. Commented Aug 30, 2023 at 12:50
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    When I got something caught in my derailleur, the plastic disc shattered and the chain got quite stuck between the cassette and spokes. The spokes were only a little more chewed up than this and two snapped between 70 and 130km later.
    – Chris H
    Commented Aug 30, 2023 at 15:54
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    @Burki the plastic disc didn't make things worse, but it didn't help either. It can help if the limit screw becomes badly adjusted. Breaking spokes are definitely a safety issue for a few reasons. One snagged my chain, locking up the back wheel. I unclipped in time to get my foot down and there was no traffic. The wheel deforming can also jam it into rim brakes. Getting stranded is a safety issue if you ride long distances in all weathers, as I do. BTW I assumed you meant "safety" not "security". English makes a distinction that other languages I know don't routinely
    – Chris H
    Commented Aug 30, 2023 at 19:18
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    @Chris thank you, yes, i meant safety. And thanks for pointing out the risks!
    – Burki
    Commented Aug 31, 2023 at 4:22
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Creo que la falta de mantenimiento y saver usar los camvios de velosidad, revisar vien los ajustes del rotor.


I think the lack of maintenance and knowing how to use the speed changes, check the rotor adjustments.

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    Welcome to Bicycles SE. Could you repost your answer in English please?
    – Ted Hohl
    Commented Aug 31, 2023 at 0:05
  • Welcome to the site - could you please use edit to expand your answer with more into?
    – Criggie
    Commented Aug 31, 2023 at 0:44

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