Snapped Chain Stay Roubaix SL2
- Thread starter WindyRob
- Start date
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black'n'yellow
Guest
Not quite sure what the point of that site is - some of those pics show carbon bikes that have been in RTAs, where a breakage is probably inevitable - not to mention being the least of the rider's worries.
I've seen plenty of bent/broken steel and aluminium bikes over the years - but unfortunately, I never bothered to build a web site about it....
smokeysmoo
Legendary Member
- Location
- Bolton, not very far from Nob End
black'n'yellow
Guest
hardly the same issue...
smokeysmoo
Legendary Member
- Location
- Bolton, not very far from Nob End
I'm not actually getting involved in this, but just offering a possible reason for bromptonfb's post.
Pic #9 is after all a broken chainstay.
My mate had a cracked chainstay on his Cannondale Supersix which Cannondale said must have been caused by an impact and refused to replace it. He got it repaired successfully though, almost invisbly, for less than £100 at a place I had used and highly recommended.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
Let me know if it would be of any use to him.
black'n'yellow
Guest
that's true - I just meant that the circumstances seemed to be completely different, that's all.
RecordAceFromNew
Swinging Member
- Location
- West London
Sorry black'n'yellow I am really struggling to understand why you continue to insist and believe your "hanger/rear mech should fail" for chain too short thesis must be correct, from originally:
and after Mickle said bent hangers is not a necessary outcome, to:
etc.
Since as you admitted:
Why don't you look at a couple of photos demonstrating inadequate chain length from Park below
and ask yourself the question why would either the hanger or the rear mech fail if the chain is even shorter and tauter so that it becomes a straight line?
What seems obvious to me from those photos is that all that would look different is that the two jockey wheels would rise and fall a little respectively, meaning the mech cage would rotate up another few degrees.
So a question is if there is anything stopping that. I decided to examine a number of rear mechs I have and see whether anything exists to stop the mech cage rotating up for a short chain. Having looked at a fair range of Shimano MTB rear mechs from Tourney to XTR, I have been able to find only one, a C030 rapid rise, that has limited freedom, due to a seemingly cosmetic (!) feature, which limits the cage rotating a long way up. The vast majority have only one stop, meaning they can effectively rotate 330 degrees out of a possible 360 - their cages are free to rotate so far up, that their outer jockey wheels can easily swing up way higher than the chainstay (if it wasn't there - and unless one has a very small large front ring that eventuality is most unlikely to be relevant for the present issue)!
Further since the chain, taut or otherwise, only rides on the plastic jockey wheels, even if the mech cage does not line up perfectly in a straight line between large large looking down from above, which incidentally it does pretty well as part of the cage and parallelograms' design, it is most unlikely to impose any significant load on the mech either.
It seems to me this is what Mickle said all along, that the mech can handle short chain by design, and your suggestion that the mech and/or the hanger should fail before the chainstay when the chain is too short is unjustified.
Since the original equipment of a SL2 is a Dura Ace rear mech and not a MTB rear mech, and since I don't run many Shimano road components, we can look at its design schematic here. As you can see there is only one stop pin (item 7) against cage rotation, meaning if the outer casing containing the pivot bolt that holds the cage is round, then it will have 330 degrees or so of rotation freedom. This photo shows that to be the case.
If the above is too much theory and still too speculative for you, why don't you see for yourself by finding a bike, getting someone to hold the pedal still, pull the lower section of the chain tight towards the large front ring with one hand, and examine the vast degree of freedom the mech cage and pulleys can still give you with the other.
Imho a completely straight, taut chain between large large will not necessarily, indeed not generally, impose any unusual load on the rear mech, and therefore not the hanger.
and after Mickle said bent hangers is not a necessary outcome, to:
That's a remarkable piece of conjecture - a good entry for the Turner prize on bicycle-related creative writing..
So, all that happened as you say - and the hanger didn't fail and the mech didn't snap first..?? I'm particularly interested in why the wheel bearings would 'seize' simply because of some rapid downshifting..??
etc.
Since as you admitted:
Why don't you look at a couple of photos demonstrating inadequate chain length from Park below
and ask yourself the question why would either the hanger or the rear mech fail if the chain is even shorter and tauter so that it becomes a straight line?
What seems obvious to me from those photos is that all that would look different is that the two jockey wheels would rise and fall a little respectively, meaning the mech cage would rotate up another few degrees.
So a question is if there is anything stopping that. I decided to examine a number of rear mechs I have and see whether anything exists to stop the mech cage rotating up for a short chain. Having looked at a fair range of Shimano MTB rear mechs from Tourney to XTR, I have been able to find only one, a C030 rapid rise, that has limited freedom, due to a seemingly cosmetic (!) feature, which limits the cage rotating a long way up. The vast majority have only one stop, meaning they can effectively rotate 330 degrees out of a possible 360 - their cages are free to rotate so far up, that their outer jockey wheels can easily swing up way higher than the chainstay (if it wasn't there - and unless one has a very small large front ring that eventuality is most unlikely to be relevant for the present issue)!
Further since the chain, taut or otherwise, only rides on the plastic jockey wheels, even if the mech cage does not line up perfectly in a straight line between large large looking down from above, which incidentally it does pretty well as part of the cage and parallelograms' design, it is most unlikely to impose any significant load on the mech either.
It seems to me this is what Mickle said all along, that the mech can handle short chain by design, and your suggestion that the mech and/or the hanger should fail before the chainstay when the chain is too short is unjustified.
Since the original equipment of a SL2 is a Dura Ace rear mech and not a MTB rear mech, and since I don't run many Shimano road components, we can look at its design schematic here. As you can see there is only one stop pin (item 7) against cage rotation, meaning if the outer casing containing the pivot bolt that holds the cage is round, then it will have 330 degrees or so of rotation freedom. This photo shows that to be the case.
If the above is too much theory and still too speculative for you, why don't you see for yourself by finding a bike, getting someone to hold the pedal still, pull the lower section of the chain tight towards the large front ring with one hand, and examine the vast degree of freedom the mech cage and pulleys can still give you with the other.
Imho a completely straight, taut chain between large large will not necessarily, indeed not generally, impose any unusual load on the rear mech, and therefore not the hanger.
black'n'yellow
Guest
jesus - that's a long question.
short answer - I've seen it happen, where a shortened chain and too much cross-over resulted in a broken mech, snapped clean through on the body just below the mounting point. It was a while ago now though. I don't know how it happened, but it did. I wasn't drunk at the time and I didn't imagine it. I don't disagree with your theory and 9 times out of 10 it is probably correct.
short answer - I've seen it happen, where a shortened chain and too much cross-over resulted in a broken mech, snapped clean through on the body just below the mounting point. It was a while ago now though. I don't know how it happened, but it did. I wasn't drunk at the time and I didn't imagine it. I don't disagree with your theory and 9 times out of 10 it is probably correct.
Rohloff_Brompton_Rider
Formerly just_fixed
don't feed the troll!
black'n'yellow
Guest
You're a proper character, aren't you? Control yourself, fella - someone's obviously been over-feeding you. You seem determined to get a rise out of a well-worn internet phrase, but it ain't going to work.
I think I'll just leave you and your petty insecurities to it. Sorry that my opinion is different to yours*.
*Actually, I'm not.
OP
OP
WindyRob
Veteran
- Location
- On the doorstep to the Southdowns
I know this has gone off the boil but there was a fair bit on interest in just how damaged the frame was. These images were taken by the shop and sent to Specialized. Perhaps the most telling image is the damage to the bottom bracket area. The replacement arrived on Friday; the SL3 pro frame is a different beast compared to the SL2 one that broke, in white and black it looks the mutts as well.
Rohloff_Brompton_Rider
Formerly just_fixed
So has Specialized resolved this to your mate's satisfaction then Rob?
OP
OP
WindyRob
Veteran
- Location
- On the doorstep to the Southdowns
Yes, the bike arrived last Friday all set up. The frame, an SL3 Pro is stunning and a very different beast from the previous one. He has had to pay for the frame under the specialized crash replacement scheme plus the failed components a chain and the rear derailleur. He did try to get them to fund the replacement but they wouldn't. Given the quality of the bike he is now riding he's happy and getting fitter and fighting back from being so ill by riding it; which I think is a good result.
