Snapped Chain Stay Roubaix SL2

[black'n'yellow]

don't feed the troll!

mate - I'm not trolling - don't be silly. I just think it just takes more than a "trust me, I know" statement to win an argument, that's all. The fact is, the only one with all the info is the OP and/or Spec themselves, so the rest of us may as well not bother...

 

[Mr Celine]

The derailleur cage rotates so it's in line with the chain, the chain would squeeze the jockey wheels, but that force is perpendicular to the chain tension. Then the weakest part of the structure fails, which by the look of it was the chainstay, which broke where it bends outwards under the bending moment due to the chainring being outside of the stay, which is oval and weakest in that direction.

But the largest sprocket is considerably further inside the stay than the chainring is outside it, so the bending moment would be pulling the chainstay inwards rather than outwards. If the quick release failed and the axle was no longer held securely by the other chainstay it is possible that there would be an outward bending moment on the drive side chainstay - we need more pics, particularly of the inside of the other chainstay as I'd expect the tyre to have contacted it in these circumstances.

My own experience of a too short chain was returning from the LBS where I'd taken a week old bike back for them to fix a couple of stiff links. They apparently cured this by removing the offending links. I was new to cycling at the time and inadvertently tried to change to big/big combination which resulted in the chain instantly locking solid. It did not cause any bearings to seize or the rear wheel to lock, it would still freewheel forwards, but the chain would not move in either direction.

 

[raindog]

I was new to cycling at the time and inadvertently tried to change to big/big combination which resulted in the chain instantly locking solid. It did not cause any bearings to seize or the rear wheel to lock, it would still freewheel forwards, but the chain would not move in either direction.

sounds right

before chainstay failure, I would have thought
a - the chain would jam or lock-up
or b - the chain would break
or c - the mech cable would snap when trying to force the mech across to the biggest sprocket
or d - the rider would think "ayup, summat not right here" and get off the bike to inspect.
or e - the chain would be so tight the cranks would no longer turn, which is another version of 'a' really.
but that's just my very humble opinion, and I'm not a troll

with a single speed bike it's possible to tension the chain so tight the cranks won't turn, but it doesn't fold the rear triangle up.

 

[mickle]

yep - so you keep saying. Not seen much evidence of that though...

Would you like to see my credentials?

 

[Andrew_P]

Way off how the thread has developed, but you are on a ride as part of team across America someone bails out due to a heart attack and someone decides to ride their bike? And then when the borrowed bike chain fails they decide rather than switch back to their own bike they carry on riding a bike with a short chain? Cannot imagine any circumstance or bike that I would rather ride across America other than the bike I own and started out on let alone riding a bike with a short chain when my bike (I assume, I know you should never assume) is on a support car/van?

 

[black'n'yellow]

Would you like to see my credentials?

Yes, that's kind of what I've been getting at these last few posts. Let the willy-waving begin...

 

[black'n'yellow]

Way off how the thread has developed, but you are on a ride as part of team across America someone bails out due to a heart attack and someone decides to ride their bike? And then when the borrowed bike chain fails they decide rather than switch back to their own bike they carry on riding a bike with a short chain? Cannot imagine any circumstance or bike that I would rather ride across America other than the bike I own and started out on let alone riding a bike with a short chain when my bike (I assume, I know you should never assume) is on a support car/van?

the thread has developed into a dispute over which part should have failed first - but I agree, it is rather odd when you put it that way...

 

[mickle]

Yes...

Nah.

 

[amaferanga]

Yes, that's kind of what I've been getting at these last few posts. Let the willy-waving begin...

He's a know-it-all. That's his only credential.

He's probably right on this occasion though.

 

[mickle]

He's a know-it-all. That's his only credential.

He's probably right on this occasion though.

Thanks. I think.

 

[Smokin Joe]

with a single speed bike it's possible to tension the chain so tight the cranks won't turn, but it doesn't fold the rear triangle up.

It wouldn't, because there is no sudden load through the tranmission like you'd get from a gear change to a larger sprocket and you'd be unable to get enough tension in the chain simply by pulling the wheel back as you tighten it. I agree with Mickle here (I'm also form an engineering back ground if that matters), the load would be along the chainstay (the shortest distance between sprocket and chainring, force travels in a straight line) and not the hanger.

 

[oldfatfool]

The op just states at some point whilst climbing a hill the chainstay snapped. I would now like to hear first hand or at least second hand wether this failure happened when they decided to change gear and the cassette jammed and the break was instantaneous or wether they where simply riding up hill and the chainstay failed.

The former and I will agree that the chain length was the cause or the latter and it was an inherent fault from some other cause. However I would still argue that the bike should be built to tolerate such a force (either by a weak link (litterally or mech hanger) or structurally itself) imo the frame should not be the weakest point.

 

[Rohloff_Brompton_Rider]

How's about you AND ColJ?

Can I wash my brain please?

the dance of the great white whales!!!....

 

[black'n'yellow]

He's a know-it-all. That's his only credential.

that's the impression I already had..

He's probably right on this occasion though.

Well, he must be right, because he keeps telling everyone. Shame about the credentials though. Clearly, I just need to 'believe' a bit more - and question a little less...

 

[WindyRob]

Sorry i don't have any first second or third hand knowledge of at what point the failure occurred. I'm riding with the bloke who owns the bike tomorrow after lunch, no doubt this thread will come up in conversation. The original question was more to gauge if this is common or not. It seems that there is some experience of this sort of thing happening to others. A quick google of carbon frame failure throws up some frightening pictures, I have now decided to descend all hills at speeds equal to or less than 7.8 mph