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I come primarily from a road background where chain breakage is relatively uncommon (or at least it has been for me). I have now started racing xc and I have been surprised by the frequency I see people with broken chains at the races. Why is this so? I normally do not think about breaking a chain on either road or cyclocross but I have seen quite a few broken chains so far at mountain bike races.

I normally change chains when the chain tool indicates too much elongation, is it ok to do the same for mountain bikes or do the chains need replacing more frequently?
 

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It's probably a combination of things.

Road chains stay much cleaner.
Mountain chains seem to require much more cleaning and lube as a result and it is unlikely that everyone does this (I have a Friend who rides mostly road and refuses to clean and lube his mountain chain until it just completely fails to shift--he's an idiot--because he doesn't ever have to on his road bike.)
Mountain chains experience more tension, the smaller chain rings mean the same pedal force drives the chain harder.
Mountain chains probably experience high tension quite often and for longer periods of time than road chains, even with the same rider.

Keep in mind the dura ace 9 speed chain is the same as the xtr 9 speed chain so the chains at least used to be the same.
 

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Mountain bike chains get abused a lot more. With the highly variable terrain in mountain biking, and especially in the stress of a race, we often end up slamming off hard multiple shifts under heavy load which is not good for anything. We should know better, and most of us do, but it ends up happening anyway in the heat of the race. At the same time everything's getting bounced around hard and caked in dust, mud, water, vegetation, and who knows what else, it's just not a fun life for the chain and the rest of the drivetrain.

Another thing to consider is that road cassettes are generally spaced 1 tooth apart on average for the most part so it's easy for the chain to move smoothly between one cog and the next. Mountain bike cassettes usually jump 2-3 teeth between cogs which puts more stress on the chain when it's moving from one gear to the next.

Bottom line. The chain is under more tension, gets slammed around harder from one cog to the next, gets flexed the wrong way more often when we force shifts, and on top of all that it gets caked in a bunch of crap from riding on trails.

As for replacement, I rarely break chains since I'm still using the stronger 8spd stuff from the old days so I just go by chain wear.
 

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I say its all about the shifting- larger jumps between cogs. I say this because I've used an 8spd chain for my SS, never ever ever cleaned it, rain, mud, rust, cyclocross, torqued the crap out of it, it creaked and whistled a lot, but never broke until I finally felt sorry for it after a couple years and swapped for a real SS chain.

Also, I think some people are just really bad at shifting- they either have poor finger-leg coordination or think its ok to shift under high torque. And then they claim its because they have so much power.


Interesting note: since I've been on 1x9, all 3 of the chain break issues i've had in the past 1.5 years has not been a full break. I start feeling a knocking or slipping every 3-4 pedal strokes, the chain is still holding up even under high torque, finally it either bugs or worries the hell out of me so I get off and examine find a bent link. Better than having it shatter mid-stroke up a climb i guess.
 

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I can't say for sure, but I agree with most of the above. Maintenance may have something to do with it, but most likely it's poor shifting. On the trails, there are a lot more "panic" shifts under load. I never find myself dumping gears on the road, but I do sometimes on the trails.

I don't really ride geared mountain bikes much anymore, but I've been fortunate over the years. The only time in recent years that I've broken a chain was totally my fault... I shifted gears during an acceleration of a sprint. It was dumb and I knew better. The chain snapped and almost sent me to the ground in a heap.
 

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It could be that the chain was damaged by a rock. Often the front chainring can smash into a rock causing the plates on the chain links to weaken.

Another culprit is re-using chain pins. You never want to re-use a chain pin. Either use a master link, or buy new pins. Back when I didn't know better, I used to re-use chain pins and I had a chain blow up on me under load. I'll never do that again.
 

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Nope...most chain breaks are poorly executed shifts....by hypoxic people....trying to win a race.

Change when your chain tool indicates....keep lubed and clean.
 

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Only poorly executed shifts on a mountain bike? It's rare to see broken chains on a road bike (it can happen, but not as often)

I guess roadies know how to shift their bikes better....

Also, what about those of us who don't shift all? (singlespeeders). I see people bust SS chains all the time.
 

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Only poorly executed shifts on a mountain bike? It's rare to see broken chains on a road bike (it can happen, but not as often)

I guess roadies know how to shift their bikes better....

Also, what about those of us who don't shift all? (singlespeeders). I see people bust SS chains all the time.

I've trained and raced my SS almost exclusively since 2006. I ride a good bit and I suspect that I ride harder than most. Maybe it's just dumb luck and maybe I'm tempting fate here, but I've never broken a singlespeed chain.

I have a sneaking suspicion that most of the SS chain failures are the result of something that was done incorrectly as well. While poor shifting is obviously not the culprit here; I suspect that it could be re-use of pins, changing cogs/rings with varying levels of wear, chainline or using an unprotected chainring (read: your chain) as a bashguard. I also question the use of geared chains as opposed to a chain that is designed to run one gear only... particularly if your chainline isn't spot on I think that might be an issue.
 

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mnoutain bkie rdier
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Those LOUD snappy shifts made on mtb bikes under heavy load are chain breakers imo.

I liked the comment about hypoxic racers trying to win races..:D

They just don't happen much on a road bike because you have way more time to prepare for the hill ahead and the terrain is never/rarely as steep as the short punchy climbs on mtb.

Therefore, you see more broken chains on a mountain bike imo

Also, a road bike can be spec'd with a lousy chain and you might get by...on a mountain bike, you are really pressing your luck with a cheap chain...
 

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I've broken one chain in four years. I was riding my single speed. It was completely my fault. I converted a non single speed frame to a single speed and the chain was already worn out, but it was the only one that would fit. It stretched more as I rode it over the next two months about 80 miles a week. It got into binds, etc. due to it now being too lose and I was wanting one more ride and it broke twice. I ended up getting pulled home on the road.

With all of that said, if someone can shift smoothly (not under pressure) and change the chain often it is extremely rare to break a chain. I rarely carry my chain tool.
 

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With all of that said, if someone can shift smoothly (not under pressure) and change the chain often it is extremely rare to break a chain. I rarely carry my chain tool.
Same here, Rod. I haven't snapped a chain in many, many years. I keep it clean, lubed, and go through a few per season.
 

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Proper shifting does make the chain last a lot longer, in my first 5-8 years of mountain biking when I was learning the basics I wasn't the best at anticipating shifts to say the least, and was often forced into panic shifts under power. I used to break a chain a year on average in those days. Since then it's averaged about one break every 10 years, and it's always an early or late season ride where the chain is caked with mud and getting jammed and/or chainsucked all over the place. Sooner or later I can't backpedal in time and end up twisting & breaking the chain.
 

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i break a fair number and it is nearly always operator error, panic shifting when I might be better off dismounting and taking a hit or poorly pressed in links from hasty repairs the night before.

I'd be curious if there is a "gold standard" 9 speed chain that is less prone to breaking.
 

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Nope...most chain breaks are poorly executed shifts....by hypoxic people....trying to win a race.
^ ^ ^

Jeff has nailed it. Mountain-biker suddenly hits hill, stands on pedals, downshifts a bunch-o-gears under load. Next thing you know, kaplooie!

And they all deny it. No one ever makes a bad shift. Even when several side plates are obviously pulled sideways, denial sets in and it must surely be the chain's fault.
 

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Okay. That makes sense.

Would these chain breakers also chew up the cogs/chainrings? I suspect if they are standing on a hill and shifting, the teeth on the gears would be shredded too. I know a lot of front chain rings are aluminum, but the chain itself is steel, so I would imagine the chainring would take the most beating.
 

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Okay. That makes sense.

Would these chain breakers also chew up the cogs/chainrings? I suspect if they are standing on a hill and shifting, the teeth on the gears would be shredded too. I know a lot of front chain rings are aluminum, but the chain itself is steel, so I would imagine the chainring would take the most beating.
In my experience I've only broken one chain (it was a demo bike, the chain was clearly done anyway, half way up the first hill it snapped). I would say though that it would depend, as everything. Keep in mind the larger the cog/chainring the more the force can be distributed over it.
 

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^ ^ ^

Jeff has nailed it. Mountain-biker suddenly hits hill, stands on pedals, downshifts a bunch-o-gears under load. Next thing you know, kaplooie!

And they all deny it. No one ever makes a bad shift. Even when several side plates are obviously pulled sideways, denial sets in and it must surely be the chain's fault.
I witnessed exactly this last night at a race... it happens..
 
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