Uneven Chain Tension- Mtbr.com
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  1. #1
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    Uneven Chain Tension

    I'm kind of new to single speeding so there could be an obvious answer but I would be surprised if this is a common problem.

    I tightened my chain by pulling the wheel back and now I've found that the tension in the chain varies depending on the crank position. If I turn the cranks backwards I can feel that during a portion of the circle it is more difficult to turn the crank. It is also visible that the chain is tighter during that part of the circle. The extra resistance is felt for about a quarter of the turn.

    As far as I can tell by eyeballing, the wheel and the crank are straight, as is the chainline. The bike is a 2017 Kona Unit that I bought very slightly used about six months ago. It has less than 500 miles on it and hasn't been wrecked or otherwise damaged.

    Any advice or ideas would be greatly appreciated.

  2. #2
    One Gear
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    There is usually some play between the crank bolts and the holes in the chainring. Set the chain tension based on the tightest spot in the crank circle. Mine does the same thing and has for 10 years.

    Good luck


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  3. #3
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    Ah, so the chain ring is probably not exactly centered on the crank. That makes sense. I've been racking my brains trying to figure this out.

    Thank you!

  4. #4
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    No chainring is perfectly round. A good quality ring will be close, but there's always some variation. The way the ring is mounted can play a part as well. We all live with a tiny amount of variation, but if it's enough to allow the chain to derail, you probably need a new chainring.

  5. #5
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    Quote Originally Posted by EverRed View Post
    Ah, so the chain ring is probably not exactly centered on the crank. That makes sense. I've been racking my brains trying to figure this out.

    Thank you!
    Loosen the chainring bolts slightly and spin the crank sometimes it can center itself fairly close, better than it was at least.
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  6. #6
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    ^ this, and also tighten the chainring bolts like you would stem bolts. Small turns and in a cross pattern, preferably with a torque wrench if possible.
    I don't know why,... it's just MUSS easier to pedal than the other ones.

  7. #7
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    12Nm and Loctite 242 for steel bolts.

  8. #8
    ILIKEBIKES
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    I had a Shimano Bio-Pace chainring on my road bike when it was singlespeed/fixed- never had an issue. I asked a reliable fixie shop mechanic about it and he said it would likely not be an issue either for the same reasons as above- no chainrings are perfectly round.

    I did not notice any weird wear on the chainring.
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  9. #9
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    Thank you all for the suggestions. I now see that this is a common issue, and I've found the Sheldon method. I'll play with it over the weekend and report back.

    Sheldon (scroll down): https://www.sheldonbrown.com/no-derailers.html

  10. #10
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    Just remember, your chain only needs to be tight enough to not derail. Look at some pro track bikes and you'll see a fair number of slack chained bikes.

    Bottom line being that I don't run as tight a chain as I used to, and the tension variation is less noticeable.

    The tight spot should also be where you set your tension. Don't tighten at a loose spot and then grind your bearings with an over-tight section of chain.

  11. #11
    Always in the wrong gear
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    Uneven Chain Tension

    I went to a direct-mount crank (RF Turbine) and this problem ceased to exist.
    I even use an oval ring and have less tension variation than a round 4-bolt ring.
    Cranks+ring are lighter than XT, chain rings look nicer (more bling!) and I never have to fiddle with chainring bolts again.

    Absolute win.


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  12. #12
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    Quote Originally Posted by Shinkers View Post
    Just remember, your chain only needs to be tight enough to not derail. Look at some pro track bikes and you'll see a fair number of slack chained bikes.

    The tight spot should also be where you set your tension. Don't tighten at a loose spot and then grind your bearings with an over-tight section of chain.
    Good advice. Seems common for new SS'ers to run excessive tension on the chain.

  13. #13
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    Quote Originally Posted by EverRed View Post
    Any advice or ideas would be greatly appreciated.
    Chainrings aren't perfectly round. Try not to make the chain super tight. It should have just a little slack in it to account for the variances in the chainring and cog.

    Sent from my Moto E (4) using Tapatalk

  14. #14
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    Thank you to everyone for all of the help.

    When I went to work on centering the chain ring I found that I have an integrated crank and that there was no room for any adjustment. The variation is not extreme and so I'll be fine with just living with it.

    BTW - the crank is a FSA Comet Modular.

  15. #15
    Armature speller
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    Quote Originally Posted by commuterbik View Post
    Chainrings aren't perfectly round. Try not to make the chain super tight. It should have just a little slack in it to account for the variances in the chainring and cog.

    Sent from my Moto E (4) using Tapatalk
    They better not be round, I paid a lot of money to make sure they weren't.

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