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I have a problem of my chain dropping. What happens is when we stop and I unclip from the pedals, the crank rotates in reverse and the chain drops. I am in the large chain ring when this happens.

Could it be that my chain is too short and the tension from the derailleur is causing the crank to rotate in reverse. I have no problem changing into the lowest gear.

I have a larger chain rings on this bike what has resulted in me riding in the large chain ring and the large cog, cross chaining, or higher on the rear cog more often.

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    If you put the chain into big chainring and small cog, does it still happen? I get this when backing my road bike out of storage.
    – Criggie
    Commented Jul 1, 2020 at 23:23
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    I've seen this happen on some bikes. The rear derailer spring yanks the chain back and it sort of overshoots. Commented Jul 2, 2020 at 0:02
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    If you can change gear to the largest sprocket and largest chainring then the chain is not too short Commented Jul 2, 2020 at 10:12
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    Have you properly set the limit screws? Commented Feb 4, 2021 at 22:20
  • Have you simply tried doing what it takes for it to happen and watching it? Maybe video? How does the chain fall off? What side? Lower side first? Etc. Help us to help you. Commented Nov 11, 2023 at 5:49

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Having your cranks rotate while walking the bike in reverse could mean your chain is too tight, needs lubricant, or your rear hub needs lubricant or service. There are a few types. Start with lubing your chain?

Dropping the chain is a bigger problem and is likely an issue with your chain line. The problem could be:

  1. You have a 2x or 3x drive train (multiple chain rings in the front) and while in the large chain ring and the largest rear cog (in the back) you back pedal and it falls off the cog. This is called "cross chaining" and it happens because a 2x or 3x system is not designed to do this. When shifting to harder or easier gears you should check and adjust the front or rear shifter to keep the chain line consistent to avoid wear, noise, and chain drop.

  2. You have a 1x drive train (one chain ring up front) and while in the largest rear cog you back pedal and drop the chain. Your chain line typically can be incorrect if you have the wrong offset on your bottom bracket, cranks, or rear cog. For example, if you have a boost chain line bike and are missing a spacer on your bb or have the wrong offset on your chain ring (it should be 3mm).

Chain line problems can be from a variety of issues. See this Park Tool chain line article to dive in.

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    The first part of your answer is incorrect. Having cranks rotate backwards when walking the bike in reverse is normal. That is how freehubs work. Nothing to do with the chain being short Commented Oct 10, 2023 at 8:16

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