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  1. #1
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    Chain drop off

    Anybody having issues with chain coming off rear cog?only on out of the saddle climbs. In short, I put an origin8 18t cog on my superfly ss. Had a 20t chris king. Chainline is spot on. Chain tension is good. Never had an issue before. I have 2 theories. 1-the origin8 cog is flexing, it would have to be alot to jump off. 2-the teeth on the origin8 are not shaped like the c.k, although i have seen the generic polished steel rings on other ss and nobody has an issue. Anyone have any clue?

  2. #2
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    What's your rear axle setup like? QR or bolt-on? I have only experienced this twice on different bikes. One was steel, and the frame was toast... flexed enough at the bottom bracket/chainstays to derail the chain. The second was due to running a QR (in horizontal dropouts no less) and a 32x22 technical climbing gear.

    Also: double check your chainline with good tools (couldn't hurt) and maybe try setting the sprocket ~1mm to the inside of the chainring. This way, most flex due to heavy torque would only serve to correct the slight misalignment.

  3. #3
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    qr on sliding horizontal dropouts. carbon ss frame with race x lite wheels.

  4. #4
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    Forgot-pc7x ss chain

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    Sounds like a nice light build, but with enough compliance to make loaded flex an issue.

    Definitely try moving the cog inwards around 1mm to make sure that when there is flex, it 'corrects' the chainline. Depending on your cog and spacers, you may wind up anywhere between 1mm and 1.5mm to the inside relative to the chainring. Not enough to mess things up in normal riding, but should keep the chain on during heavy climbing.

    Also, if your wheelset did not come with an internal cam QR, pick one up and throw it on the rear. They provide a much more positive engagement.

    I'll withhold my opinions on SRAM chains, as many others have used them without problems.

  6. #6
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    I am wondering about the chain itself now. I have been running pc7 for about 6 mos now. Just raced a 6 hour race at rocky gap-took 1st thank you:0 anyway, I have gf rigs in the shop running z chains, which strangely enough are geared chains and narrower than the pc7. I am wondering if the chain being wider on that particular cog is the culprit. Again no issues with chris king and that chain-only when i went to the 18t origin8 cog which is slightly narrower than the ck.

  7. #7
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    Quote Originally Posted by el davido
    Forgot-pc7x ss chain

    The chain is the culprit. I had the exact same issue with my bike. I switched to a dura-ace xtr chain and it hasn't skipped since. A fellow SSer pointed it out. The SS specific chain is wider than the cogs causing slop. The twisting of the frame in the out of the saddle climb is causing it to skip off. The XTR chain is narrower and it doesn't have the extra space to skip.

    $35 at performance bike. More expensive but worth it.

  8. #8
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    I am a sram fan. I just got a big shipment from trek today and I have some 870 8spd chains in. Is the 9speed to narrow? Any binding?

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    Quote Originally Posted by el davido
    I am a sram fan. I just got a big shipment from trek today and I have some 870 8spd chains in. Is the 9speed to narrow? Any binding?
    The chain was too loose. the XTR chain fits a bit tighter on the chainring and cog (both surlys).

  10. #10
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    My question is -how in the world does a chain jump off the rear cog like that when you have proper tension? Especially when your are climbing which is actually making the chain tighter. Any breakage issues using a gearing chain? Are you using a quick link?

  11. #11
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    Adding- Why didnt this happen with the Chris King cog using the same chain?

  12. #12
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    A -- Stand next to your bike and put the front brake on. Now stand on the drive side pedal and watch the bottom bracket. Repeat on the other side. Get someone to help you measure just how much movement there is.

    B -- Check the thickness of the sideplates on your chain. Multiply this number by 1.5. This is the amount of deflection/flex under load you need to potentially derail the chain.

    If measurement A is greater than or equal to measurement B, now you know why this can happen. Of course, it doesn't always happen. The conditions have to be just right. I was never able to do it at will. But steep climbing, lots of power, rocks and bumps, and yep off comes the chain about once every half dozen rides or so.

    Moving the cog in ~1mm seemed to help alot. Getting a frame that wasn't quite so noodly helped more. Chainrings and cogs with no ramps and square profile teeth can help as well.

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