From today's ride:
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My best guess is that the chain has worn straight through the lower section of cage, ending up catching itself on the resulting sharp corner (lower right) and getting dragged into the wheel. Just recently swapped the jockey over as the old one was a bit worn out, and noticed whilst riding today that the chain was popping off and rubbing on the cage. Has that happened to anyone here?
The hanger is fair bent, hopefully nothing that the LBS can't fix with their magic bending stick.
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Or this could have affected it:
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which must have been quite impressive to watch, as I was hooning in the direction of the photograph at the time, and the closest tyre track was about 5 feet away. Though the hanger wasn't bent at that point though so who knows.
Interesting ride...