Chain too short? new failure mode



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Ron Hardin

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After a few weeks of salt snow slush grunge spray, the chain skipped off the big front chainwheel
(snow on chain from wheel, probably) and managed to pull the derailleur into the spokes, where it
had been on the big freewheel cog. The chain had been popping off for a few days in the snow

There's no question that the derailleur stops were set correctly; it must have been that the chain
bent the derailleur to contact the spokes, being a short chain for the situation (stock SRAM-PC48
chain, 114 links).

The derailleur must bend to shorten the run when required, being what gives in the situation. That
pulls the bottom end of it into the spokes, no matter how the derailleur stops are set.

Oddly enough, the wheel appears to be undamaged. The derailleur is a mess, sort of a pretzel.

Meybe I'll hunt out one of the old big spoke protectors off an old bike and replace the existing
small one.
--
Ron Hardin [email protected]

On the internet, nobody knows you're a jerk.
 
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Mikeyankee

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You were lucky.

About 5 years ago I had a similar occurrence, not because of chain length, but when a pebble flew up
and wedged between the chain and idler pulley, pulling the derailleur into the spokes.

I was going close to 30 mph at the time and fortunately did not crash... but will never forget the
instantaneous smell of burning rubber from the tire rubbing the seatstay.

The derailleur and chain were trashed, the wheel partially tacoed and both dropouts were badly bent.
Cost me about $400.

Mike Yankee

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