Chain Derailing Issues- Mtbr.com
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  1. #1
    Ahhh the pain....
    Reputation: Raybum's Avatar
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    Chain Derailing Issues

    All,
    I've been riding Single Speeds exclusively for like 5 years. Being a mechanical engineer that is a little OCD, I use my calipers and measure the crap out of stuff to be sure my chainline is solid. I've had the occasional chain derailing that typically I can blame on a worn chain. In other words (I run an oval AB chairing BTW), the lateral flexibility is higher on a worn chain and the lower length (not in tension) wiggles side to side more and climbs off the rear cog. AB oval rings naturally have a little tension variation and it seems like every time the derailing happens at the cog and when I'm full gas on some bouncy bit of uphill trail.
    Here are my thoughts...please feel free to share yours...
    1) The rear cog(running a Stainless Steel Wolf Tooth) flexes a little but doesn't have much in the way of chamfers on the tooth sides. In the stand, I can push the chain with my fingers and with little pressure get it to derail.
    2) Do some chains have more chamfers on the side plates? gotta figure that under a bunch of bouncy stuff, the slot on the chain is trying to find the tooth on the cog....chamfers help that rendevous to happen... running KMC 8.93 chains.
    3) Seems like tension doens't matter too much...obviously, first reaction is to tension is up, but that doesn't seem to help.


    thoughts?

  2. #2
    mtbr member
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    I've always used singlespeed chains(lately 3/32 kmc 610HX), have never experienced this problem even with a loose chain, loose enough to hit the chainstay.
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  3. #3
    Out spokin'
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    I've always used cheap SRAM 8-spd chain on my singlespeeds. I singlespeeded nearly exclusively 10 years or so. During my SS years, the only time I dropped chains was when my chain was slack. I've used lots of different cogs, from Chris King to Surly including some custom ones. I'd have to dig them out of my garage to check, but IIRC they have chamfered teeth. Raybum, if you can derail your chain with minor pressure from your fingers then I think either your chain is too slack or the design of your cog is not optimized (hard to believe considering it's Wolf Tooth, a company that makes great stuff) or a combinition of those two factors. You said it's not chainline and it derails at the back, not the front, so factors are limited.

    I remember one time my chain was coming off constantly at the crank. Turned out the chainring had one bent tooth that kept kicking the chain off. You probably already checked for this. Have you tried a different chain?

    Good luck,
    sParty
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  4. #4
    WillWorkForTrail
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    You mention chain wear - how worn is the chain? Typically, I don't start having problems with the chain coming off unless the wear gets away from me - in other words, it's usually to the point I would replace the chain anyhow.

  5. #5
    Armature speller
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    I've only had this happen on the thinner cogs. Never on a King or Surly.

  6. #6
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    How much lateral flex is there in your chainstays?

    Too much and it will exaggerate the problem once your drivetrain is worn.

    This can be a problem with bikes designed for derailleur use because the designers have assumed the chains will be guided on to the rings and rear sprockets, ie they have built a bit more 'feel' into the chainstays.
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  7. #7
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    I'm running a wolftooth cog and cannot get my chain to derail just by pushing on it.

    I suspect some is up with your chain tension.

  8. #8
    Life's a Garden, dig it!
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    Quote Originally Posted by Velobike View Post
    How much lateral flex is there in your chainstays?

    Too much and it will exaggerate the problem once your drivetrain is worn.
    This was my first thought as well. I've been riding SS on two different frames for about nine years and have never had a chain jump laterally.

    Are you running an SS specific rear hub? Or are you spacing it on a typical geared freehub body? I know you say you're measuring to the gnat's ass, but if the chainstay isn't flexing, maybe the cog is wandering a bit on the freehub body?
    "And crawling on the planet's face, some insects called, The Human Race..."

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