Chain Tight Spots- Mtbr.com
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  1. #1
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    Chain Tight Spots

    I've tried different cog sizes and chainrings (all are HBC) and still have the dreaded tight and loose spots in the chain. Next I tried the Blackspire MonoVeloce ring with the HBC cogs and that was a little better, but not to perfection that people speak of. So far my best set up has been the 14 year old stock middle ring with a 17 or 18 tooth HBC cog. The rest of the drivetrain is a XT M760 crank and FCEBB. Is perfect chain tension achievable?

  2. #2
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    no.

  3. #3
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    But you can get pretty close.

    Maybe you are not getting your chainrings quite centered on the cranks.
    Try this:
    http://sheldonbrown.com/singlespeed.html#tension

    It is even possible to have the cog so that it is not quite centered.

    "it IS possible that you are faster or slower than anybody else who is having at least as much if not more or less fun"

  4. #4
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    How's your chain? any links added at any point in it's life? I'd be happy to check the ring and cogs out for you, although i'd be suprised if that was the issue. It's hard to get absolute perfect tension because of all the variables, but it shouldn't be bad enough to bother you.

  5. #5
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    Quote Originally Posted by perttime View Post
    But you can get pretty close.

    Maybe you are not getting your chainrings quite centered on the cranks.
    Try this:
    http://sheldonbrown.com/singlespeed.html#tension

    It is even possible to have the cog so that it is not quite centered.
    yea, unfortunately nobody holds their freehub bodies to a standard dimension, so there's often times where they're undersized and you get a few thousandths of play. This is often all it takes to get a tight spot.

  6. #6
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    Quote Originally Posted by ISuckAtRiding View Post
    How's your chain? any links added at any point in it's life? I'd be happy to check the ring and cogs out for you, although i'd be suprised if that was the issue. It's hard to get absolute perfect tension because of all the variables, but it shouldn't be bad enough to bother you.
    The chain is a brand new SRAM PC870. I was shockingly surprised how much of a difference there was between the loose and tight spots. I'll check out the Sheldon Brown tech tip.

  7. #7
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    make sure the internally threaded portion of the chainring bolts are long enough to reach into the chainring as well as the spider. Some are short enough to where people tighten them and the edge is hitting the spider or ring instead of entering the hole. If ridden like that, it will tweak the crap out of the ring. Also, if a chainring bolt came loose or fell out and it was ridden hard, it can also tweak the ring.

  8. #8
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    For best results, use the chainring that came with the cranks. For example, I have some older deore square tapers and the shimano ring that came with it. I have never had tight/loose spot issues. For a short time I switched to a different ring and had this problem. I was only able to resolve the problem when I went back to using the shimano ring (which was designed for that crank).

    But honestly, I wouldn't worry about it (unless your chain is falling off). Some loose and tight spots are inevitable. Just ride it and enjoy it.

  9. #9
    The need for singlespeed
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    This is something I've struggled with on two cranksets and two chainrings. I haven't lost a chain yet but it does pop into place sometimes on fast climbs up rough terrain. Chainline's good.

    Most recently this occurs with my m960s and an HBC ring. Tight and loose spots correspond to the crank position, so it's not to do with the cog. Sheldon's trick doesn't fix it. I rotated the ring 90 degrees and the tight/loose spots occur in the same place relative to the crank, not the ring. So it seems the crank is the culprit. Perhaps the chainring bolt holes were not drilled precisely enough.

    The crank is used, so it's possible it was tweaked in a past life, although I consider this unlikely since Shimano's alloy is hard as **** and should more likely crack than bend.

    I'm wondering if Sram/spiderless would remedy my problem. How many of you guys running Sram/spiderless have chain tension variation?

  10. #10
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    There's also a possibility that your freehub is warped. Have you checked the freehub to see how straight it spins?

  11. #11
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    Quote Originally Posted by zaskaranddriver View Post
    Most recently this occurs with my m960s and an HBC ring. Tight and loose spots correspond to the crank position, so it's not to do with the cog. Sheldon's trick doesn't fix it. I rotated the ring 90 degrees and the tight/loose spots occur in the same place relative to the crank, not the ring. So it seems the crank is the culprit. Perhaps the chainring bolt holes were not drilled precisely enough.

    The crank is used, so it's possible it was tweaked in a past life, although I consider this unlikely since Shimano's alloy is hard as **** and should more likely crack than bend.
    x2.

    Exact same scenario with the exact same crank and chainring, same problem, and I've done the same troubleshooting. Seems the boltholes on the crank are just not centered. Which is weird.

    Sheldon's trick doesn't do anything because there is no clearance between the chainring bolt and the hbc ring to facilitate adjustment. I suppose one could drill the bolts slightly larger if it was really an issue.

  12. #12
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    interesting that you guys are having problems with the cranks. I've only seen that on a couple occasions, and they were Stylos. The only thing i can think of is that these cranks were never meant to be ran as a singlespeed setup, so concentricity wasn't very important. And there's absolutely no reason for them to waste the time to keep the bolt pattern within .002" when .005" would do. Tighter tolerances mean higher manufacturing expense. Kind of a bummer, but what are you going to do. I should indicate the bolt pattern on my m960 for shits and giggles.

  13. #13
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    Quote Originally Posted by wjphillips View Post
    For best results, use the chainring that came with the cranks. For example, I have some older deore square tapers and the shimano ring that came with it. I have never had tight/loose spot issues. For a short time I switched to a different ring and had this problem. I was only able to resolve the problem when I went back to using the shimano ring (which was designed for that crank).
    .


    I can honestly say this makes absolutely no sense. You may have gotten lucky in your scenario, but trust me, they do not match the chainring's concentricity (or lack of it) to the crank. They grab a ring off the rack and throw it on a crankset and toss it in a box.

  14. #14
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    Quote Originally Posted by ISuckAtRiding View Post
    make sure the internally threaded portion of the chainring bolts are long enough to reach into the chainring as well as the spider. Some are short enough to where people tighten them and the edge is hitting the spider or ring instead of entering the hole. If ridden like that, it will tweak the crap out of the ring. Also, if a chainring bolt came loose or fell out and it was ridden hard, it can also tweak the ring.
    Another cause of this problem is chainring not facing the correct direction. Since one side is recessed, if you flip the chainring (ie mounting the on the inside position showing the CR graphics) then the chainring bolts may come up short. However, if indeed the crank holes are off center, you may want to do this purposely. This would allow enough play to center the chainring (the difference between the male half and the charinring holes, which is considerable). While it would require special attention, it should be possible to tighten the chainring bolts to sufficiently hold it in place.

    <iframe width="480" height="390" src="http://www.youtube.com/embed/QkjD3D5FgmE" frameborder="0" allowfullscreen></iframe>
    Just one more rep and I get the toaster!

  15. #15
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    Quote Originally Posted by aka brad View Post
    Another cause of this problem is chainring not facing the correct direction. Since one side is recessed, if you flip the chainring (ie mounting the on the inside position showing the CR graphics) then the chainring bolts may come up short. However, if indeed the crank holes are off center, you may want to do this purposely. This would allow enough play to center the chainring (the difference between the male half and the charinring holes, which is considerable). While it would require special attention, it should be possible to tighten the chainring bolts to sufficiently hold it in place.

    <iframe width="480" height="390" src="http://www.youtube.com/embed/QkjD3D5FgmE" frameborder="0" allowfullscreen></iframe>
    My chainrings are not recessed on one side. They are completely symetrical so you can flip them over and double it's life.

  16. #16
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    Quote Originally Posted by ISuckAtRiding View Post
    My chainrings are not recessed on one side. They are completely symetrical so you can flip them over and double it's life.
    I guess I should have qualified my post that it depends on the thickness of the chainring. A Sugino single chainring bolt is about 3.9mm. A Salsa CR 4.2 mm thick so if it was not recessed, the female half will not extend into the crank hole. OTHO a TruVativ SS CR is 3.1mm, so the recessing is not necessary.
    Just one more rep and I get the toaster!

  17. #17
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    Quote Originally Posted by aka brad View Post
    the female half will not extend into the crank hole.
    quoted *just because*

  18. #18
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    Cranks with off centre bolt holes are usually the cause of eccentricity in cases where the chainring can be eliminated. My old 110bcd 5 bolt Sinz cranks were the best I've owned for not having this problem.

    I'll go spiderless next time.
    I see hills.

    I want to climb them.

  19. #19
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    What difference does it make if there are tight and not so tight spots??

  20. #20
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    Quote Originally Posted by Just1Gear View Post
    What difference does it make if there are tight and not so tight spots??
    Depends on how not so tight the not so tight spots are.
    I see hills.

    I want to climb them.

  21. #21
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    IMO worrying about this whole tight / loose issue is a waste of time. May I suggest everyone lower their expectations and move on.

    Having a crank that's not "perfectly" concentric is like having a drop dead gorgeous girlfriend with one breast slightly larger than the other. That's just how it is... stop worrying about it and just enjoy.

    If it occupies your mind, you're not riding your bike enough.

    Either that or you're not riding your girlfriend enough, depending on which "problem" is occupying your mind.

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    We get old because we quit riding.

  22. #22
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    ^^^ This +1 Sparty. The tighter you have your chain the quicker the bearings are going to wear and the more friction/ resistance you will have trying to turn over your crank. Just pull your hub tight, hit the chain with wrench, tighten skewer or bolts.

  23. #23
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    Quote Originally Posted by Sparticus View Post
    IMO worrying about this whole tight / loose issue is a waste of time. May I suggest everyone lower their expectations and move on.

    Having a crank that's not "perfectly" concentric is like having a drop dead gorgeous girlfriend with one breast slightly larger than the other. That's just how it is... stop worrying about it and just enjoy.

    If it occupies your mind, you're not riding your bike enough.

    Either that or you're not riding your girlfriend enough, depending on which "problem" is occupying your mind.

    --sParty
    But what if my girlfriend is sometimes tight and sometimes not, depending on which way I turn her?
    Sometimes, I question the value of my content.

  24. #24
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    Quote Originally Posted by ISuckAtRiding View Post
    I can honestly say this makes absolutely no sense. You may have gotten lucky in your scenario, but trust me, they do not match the chainring's concentricity (or lack of it) to the crank. They grab a ring off the rack and throw it on a crankset and toss it in a box.
    Ok. But that was my experience (whether it makes sense to you or not).

  25. #25
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    I also have no problems with my square taper Sinz cranks.

  26. #26
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    I'm running HBC front and back on a Bontrager Race Lite SS spiderless crank and have the issue.
    Remember, nobody knows. So let's find out...

  27. #27
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    Quote Originally Posted by Sparticus View Post
    is like having a drop dead gorgeous girlfriend with one breast slightly larger than the other.
    For every beautiful women there's a man out there that's tired of ****ing her.

  28. #28
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    Even when brand new my freehub had some minor and normal wobble to it. No matter what crank, ring and cog I use I know I'll always have some tighter spots. It's kinda comforting actually, because I don't feel a need to keep chasing after perfection now

  29. #29
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    Quote Originally Posted by Martin6 View Post
    Is perfect chain tension achievable?
    yes.
    HBC spiderless on SRAM XO + chris king on hope is perfect... or near enough to perfect that this engineer can't tell any variation.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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