Originally Posted by
FBinNY
Just speculating so factor that.
With the understanding that modern chains have plates thinned to the point of having minimal safety margin, we can expect greater instances of breakage owing to variables.
There's always a tolerance in manufacturing precision, alloy formula, heat treating, etc, so there's always a weakest link. With little margin for error, what used to be OK no longer is.
However, I'm not convinced that the failure near the master link is coincidence. 66:1 odds (either side of connector in 122 link chain) argue against that.
So consider that each inner plate carries half the load roughly equally, and can't carry much more.
The dimensional precision of the connector is more complicated than the normal plates, so it's conceivable that one side is a bit off. That would alter the 50/50 load sharing of the adjacent inner plates, taking the harder working one above the fatigue limit, and eventually to failure.
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BTW I noticed some nicking of the outer plate in the photo. This is usually caused by shifting under load. Not that it caused the break, but it is hard on chains and not a good thing. If you see much of this type of damage, take a hint and try to time your shifts better.
Well, when I first had odd behavior in 11th and 12th gears, it was about 5 miles into a ~70-mile ride. I'm sure the skipping was caused by a fully broken inner plate. Point being, I put 60+ miles on the chain with that broken plate. While I wasn't sprinting, if the plates were that marginal, I would think as soon as one plate broke the other would follow.
But no question 12-speed chains have less material then 11-speed which have less than 10-speed. So, all other things being equal, they can't hold up as well. Of course, all other things may not be equal.
I also agree that I don't think breaking at the master link is a coincidence. I lean towards stress when the chain was "broken" for sizing when the bike was built. I assume the bike builder is working pretty fast and pulling chain to length with some powered machine that quickly pushes the pin out of the chain. If that builder were perhaps a little too quick to pull the chain free and twisted it a little with some force, maybe they stressed it. Or maybe the machine needs adjusting. No way to know.
Another possibility is stress when I've snapped the master link on and off. I know I did this at least twice. First to take the chain off to strip it when new and another time when I swapped out the crankset. I use the Park Tool Master Link Tool for this. But I don't think opening the master link would stress the inner plates at all as you're squeezing the master link itself. Of course the pliers do apply tension to snap the master link back into place, but I don't think this is anywhere close to the max forces seen riding the bike. But still maybe something about the "snap" itself is a transient stress.
Originally Posted by
mpetry912
you got acceptable life out that chain at 4000 miles.
Do you monitor chain wear with the Shimano guage ? a worn chain will wear out the cassette
ONCE in my cycling career I had a chain do this. Still got me home with careful riding.
Stuff does break. I replace chains when they start to show wear. The Shimano chains are exceptionally good.
2500 miles is an acceptable life, at least to me
/markp
As I mentioned in my original post, the chain has no measurable "stretch". I use a Pedro's Chain Checker.
Yes stuff does break. And in this case I was mostly curious to see if this type of break is common in 12-speed chains. It doesn't sound like it is. But I know I've seen some post online and it does seem that 12-speed chains have more issues.
While I can't complain about 4,000 miles out of a chain, I'd expect wear rather than breaking.
Originally Posted by
zandoval
Could it be constant shifting under load?
Could this a Brifter use technique problem?
As I mentioned in my original post, I know how to shift gears. But of course, we all have a bad shift once in a while. I estimate ~50,000 shifts over the 4,000 miles on the chain. A few of those are going to be bad.
But I suppose one bad shift in just the right way may be all it takes.