I’m having an issue with my chain falling off the lower pulley wheel when (1) I hit a significant bump or (2) shift from large ring to small ring. But only in cogs 6, 7, 8. Any suggestions? I’ve checked derailleur hanger, put on a new chain, checked chain length, adjusted micro shifting and it still does it. Groupo is a year old, never crashed, and is on a Canyon Ultimate CF SLX. Thanks in advance.

  • My first suspicion is that your chain is too long. After that, a bent hanger or cage or something amiss with the tension spring. – Daniel R Hicks Feb 4 '19 at 2:31
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    I am a bit confused, how does the chain drop from the lower pulley wheel? The cage holding the pulley wheels usually fits quite tightly, there really isn't any extra room for the chain to dislodge into. Does your lower pulley wheel have broken or missing teeth? A picture a chain that has fallen off the lower pulley wheel could be useful. – Rider_X Feb 4 '19 at 8:18
  • Getting better at avoiding "significant bumps" is always a good idea, even after you've fixed your derailleur problem. – David Richerby Feb 4 '19 at 10:15
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    If the chain is falling of a derailleur cage pulley (and I assume that is really what you mean as you mention the problem occurs in cassette sprockets 6-8, so you are not talking about the chain falling off the cassette) there is something very wrong with your cage. There simply is not enough room in the cage for the chain to come off a pulley. Photos of the derailleur would probably help. – Argenti Apparatus Feb 4 '19 at 13:16
  • Thanks guys (and gals). I should have included pix, sorry about that. At the time of posting I was going through the process of elimination. To clarify, the chain would become misaligned enough on the lower pulley to rub the inboard side of the pulley. After new chain, aligning RD hanger, tightening crack, it turns out that Rider_X had it right: the lower pulley wheel teeth were worn, I'm not sure why or how, after only a year, but under a magnifying glass I could see how different (worn) they were from the upper pulley wheel. I changed both upper and lower. No more issues! Thanks! – Tri Coach Feb 6 '19 at 14:34

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