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I am new to this so I wanted to know if this behavior is normal. When I pedal backwards and the chain is on the smallest sprocket I can see that the chain rubs for a second and then does a little jump. The hanger is straight; indexing and everything is adjusted. This also happens on the second and third lowest sprockets but the jump is smaller.

I did not see this happening when pedaling forward.

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    Probably depend a little on what exactly "jump" means. Being as this happening on back peddling instinct would suggest the chain line is off somewhat. Is there maybe supposed to be spacers on the front chain ring?
    – Hursey
    May 4, 2023 at 0:04
  • that's a 3 weeks old bike and I noticed that this is happening when I was cleaning the bike. Maybe they forgot to add spacer? I will investigate today evening and if nothing found, I guess it's time to bring my bike to the dealer. The main thing is that you just told me that this is not normal behaviour. Thanks!
    – notFake7
    May 4, 2023 at 9:16
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    Unrelated to the question: As a cyclist it's worth knowing that peddling is not the same as pedalling. End of PSA May 4, 2023 at 12:34
  • @user2705196 sorry, autocorrect took over
    – notFake7
    May 4, 2023 at 21:10
  • More details needed here. I am assuming that you are referring to the 11-tooth sprocket (smallest) on the vast majority of Shimano 11 speed road drivetrains (exceptions being a 12 or possibly higher, but not very common). You also mention 34T in your title. Are you referring to your front chainring (a 50/34 crankset)? Or are you referring to your cassette in the rear (an 11-34 range)? You have not provided quite enough information to actually answer the question (we need the additional details). Otherwise we would just be guessing. And guessing is not an answer. Please add the detail, thanks.
    – Ted Hohl
    May 5, 2023 at 17:57

2 Answers 2

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It's pretty normal to get minor chain jitter and even hopping between sprockets if you pedal backwards at the extremes (highest/lowest gears). The answer is probably just "don't do that". If everything works ok when you pedal forwards there's nothing to worry about.

The reason is, if your chain is going backwards, it isn't going through the rear derailleur before it's hitting the cogs at the rear. So it will have a tendency to drift towards center (or more accurately, towards a straight line-up with the front chainring) which won't be corrected by the rear derailleur.

If you need to roll your bike backwards for whatever reason, try to shift into a middle gear first.

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  • The chain will also tend to go slack as friction in the jockey wheels of the rear derailleur will cause it to be pulled forward. Chain goes slack, and a slack chain without guidance can go anywhere. Now, throw in cross-chained small-small for an even looser chain and more friction, and then the friction of going around the smallest cog jumping into the fray.... "[D]on't do that" is indeed the answer. May 12, 2023 at 22:52
  • I eventually decided to bring the bike to the dealer. I was told not to worry about it as long as pedaling forward is good. Thanks!
    – notFake7
    May 29, 2023 at 22:21
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It shouldn’t be happening. Most likely, and I suspect it even more now that you mentioned the bike is quite new, that the front derailleur is simply misaligned. That happens almost all the time - shops cut corners when installing the front mech. Proper derailleur adjustment is always the first thing I do when I buy a new bike, regardless of the price.

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    No. Just plain no. There's no way for a rear-derailleur bike to keep the chain tensioned properly when pedaling backwards as the derailleur only tensions the chain on the bottom and is close enough to the cassette to guide the chain. Pedaling forward is what keeps tension on the top half of the chain. When you're pedaling backwards, the top half of the chain can easily go slack and start jumping all over, and with no guidance near the cassette it can and will go anywhere. The fix is simple: don't do it. May 12, 2023 at 22:47
  • @AndrewHenle you are fully entitled to your opinion, it's just that I absolutely do not agree with it. Pedaling backward should not cause enough slack in the chain to cause any slapping unless done with violence at high speed, with sticking freehub, or faulty cage spring. In all my years of competitive riding I've never experience a problem described by the OP with properly maintained gear. And suggesting that pedalling backward should not be done is just laughablet. Yes, that could be done, but it does little beside masking the underlying problem.
    – Paweł
    May 15, 2023 at 18:46
  • Nothing about what I said about derailleur friction causing a chain to go slack or a chain having no guidance where to land on a cassette while pedaling backwards have anything to do with opinion - they are facts. I've ridden competitively for years, too. I've also raced with a UCI-sanctioned racing license. I also build my own bikes. May 15, 2023 at 19:10
  • @AndrewHenle that is not entirely true. The chain is still held in a fixed position by the rear derailleur and as it possesses a certain lateral rigidity lateral movement is still constrained. Moreover, during normal pedalling the chain will be closer to the center of the bike on the upper part of the casset than on the lower as the chain tension force has a non-zero component in that direction. Your experiences are vastly different from mine, and it can be due to a variety of reasons. And I still stand by what I said - the whole setup can be adjusted so that no cog jumping occurs.
    – Paweł
    May 15, 2023 at 20:33
  • And I still stand by what I said - the whole setup can be adjusted so that no cog jumping occurs. No you don't. You've already weasel-worded it: unless done with violence at high speed, with sticking freehub, or faulty cage spring May 16, 2023 at 13:33

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