We have a customer that bought a bike at one of the online brands. We fitted him on it and now after riding the bike for a month or 2 last week on a recovery ride he heard a loud snap and after that even more noise.
He almost fell of the bike and when he stopped and looked what the fck happened he saw that his rear derailleur completely snapped from the frame as well taking a considerable piece of the frame with it.
The bike was returned to the Dutch office of the brand and he got told that it was not a warranty issue since the rearderailleur git stuck in the rear wheel first and that caused the danage to the frame. For the damaged rear wheel they send him to mavic, they send the bike with the wheels from mavic but they only wanted to provide him a new frame at a cost of 1200 bucks and another 250 bucks for assembly from all the parts but for the rear wheel that is damaged he should consult mavic…
What I wonder is what can cause a rear derailleur that seemed to be working fine for like 2 months or so make it snap or get stuck in the rear wheel.
We have set up more bikes from this online company and what we found is that they almost all have really tight/short chains. Can that be a cause for screwing up the derailleur? Or any other plausible causes that can be checked?
One of the most common scenarios is that a bike falls over on the drive side and the rear derailleur hits the ground. The hangers bend pretty easily. The bike will still function pretty well until the user shifts inboard to the easiest gear and the cage gets hooked on the spoke of a spinning wheel. It’s pretty common that the rear derailleur will rotate about 270 degrees and smacks the seat stay, and breaks it.
For the simple, would a plastic spoke guard prevent this from happening?
Yeah, that’s what it’s for. The really small ones probably don’t do much but the larger ones will stop it most of the time. All the cool kids take them off though.
I think there are multiple possibilities.
Some as others mention
broken spoke catching on the deraileur.
limit stop not correctly adjusted (so deraileur goes too far)
bent hanger (from either new, or had dropped bike etc)
loose bolts ! On hanger or deraileur attachment - leading to the mech being misaligned,
or your idea of a short chain is credible (I’ve done that once - i broke a chain our on the mtb. Had to shorten the chain to fix it to continue. Later on I did a dumb shift to big sprocket whilst still in big ring… ripped off mech, that then went into the wheel).
Thanks all, I will talk again to the customer and see if he recognizes 1 of the issues. We just fitted him, but on a recovery rude I hardly can imagine that he would ride large/large chainring/cog. We are living in a pancake flat country
The bike will still function pretty well until the user shifts inboard to the easiest gear and the cage gets hooked on the spoke of a spinning wheel. It’s pretty common that the rear derailleur will rotate about 270 degrees and smacks the seat stay, and breaks it.
This happens often enough when the limit screw is improperly adjusted. Chain gets wedged between the large cog and the spokes, and things break.
Did you ask the customer which chainring and rear cog he was in?
I would guess big chainring and largest rear cog.
That would be my guess except that the bike has been ridden for a while and it didn’t happen right away.
My next guess is that they over shifted and dropped the chain to the outside on the front ring and tried to ride it back on, chain got caught on crank and then pulled the rear derailleur into the spokes.
