Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: AMuzi <am@yellowjersey.org>
Newsgroups: rec.bicycles.tech
Subject: Re: Had a wtf? this morning - Ping AMuzi
Date: Sun, 23 Feb 2025 08:59:57 -0600
Organization: Yellow Jersey, Ltd.
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On 2/22/2025 4:21 PM, Roger Merriman wrote:
> Shadow <Sh@dow.br> wrote:
>> Went out for my morning ride. Just before a rather steep hill changed
>> down and I heard a clump and the chain jammed.
>>
>> I looked back and half of my rear derailleur was sitting on the
>> asphalt.
>>
>> OMG, I thought to myself, this is almost as embarrassing as a crank
>> arm falling off. Then faced the "walk of shame" home.
>>
>> Note, I scrub chain/jockey wheels/sprockets with water and detergent
>> every 200 Km. Was almost due for a new clean. Gear change was
>> absolutely smooth until the incident. HI and LOW screws perfect, no
>> way the chain came off and "fell into the spokes".
>>
>> Note I managed to rip a spoke clear out of the wheel with the
>> breakage. What fell into the spokes was half the derailleur. I suppose
>> that'll mean a new wheel too
>>
>> 	:(
>>
>> <https://www.sendspace.com/filegroup/v/qdHDWfYEJvo99L3/MhFp6hhZL5Z8ugxHfSuN/uTo4>
>>
>> The "cleaned" in the filename is because I cleaned the EXIF metadata,
>> not the parts after the incident....
>>
>> So "wtf" happened, what did I do wrong and how can I prevent it from
>> happening again?
>>
>> TIA
> 
> Did the derailleur come apart due to impact with wheel/cassette or a
> failure and then do so?
> 
> My old commute bike, had a rear mech fail where the cage and parallel meet
> apparently was glued in place? Was an Alivio so broadly similar to the
> Tourney I think from memory, Cues which I replaced it with is substantially
> more heavily built like the MTB mech’s as to if it will last any longer?
> 
> The Alivio lasted 9 years and 19,000 miles so probably got my moneys worth!
> 
> Mind talking of Andrew I expressed surprise that front mech’s could wear
> though! My Gravel bike front mech (Sora) had to be replaced due to that!
> Only just shy of 12,000 and 7ish years old so definitely sub par, though
> have replaced like with like and didn’t really seem any reason to match the
> rest of the bike ie GRX mostly with Tiagra shifters.
> 
> Okay (at least in uk) neither of Tourney/Alivio/Sora/Cues are particularly
> expensive being £30ish for a derailleur.
> 
> Roger Merriman

Unclear but the usual failure is a worn or bent or twisted 
or not quite well adjusted rear changer.

The normal couple of millimeters between cage and spokes is 
just enough to clear but once any of the above occur and the 
cage engages a spoke, the bike+rider mass at whatever speed 
yanks that changer up and over the axle until one or more 
things either break or jam the wheel to a skid stop.

-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971