chain tension noob question- Mtbr.com
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  1. #1
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    chain tension noob question

    Hi everyone,
    I have been trying to find the proper answer to this and I am still a bit conflicted. On my 29er SS bike (the SE Stout 29er) I have the chain pretty taut between the front and rear sprockets. The frame has horizontal drop-outs (I think the proper name is track style, they are truly horizontal, opening toward the rear). It is possible that there had been some play in the drop-out and the wheel shifted some with the first couple of rides.
    Anyway, I know that in theory there should be about 1/2" movement up and down at mid-point. Does that mean the chain is supposed to be taut and I can cause that amount of movement by pushing on it? Or should I expect it to actually SAG a bit, maybe the actual 1/2"? I think I am lucky so far and both rings seem round, no points of higher tension throughout the revolution.
    I know it may sound like a silly question, but I want to make sure I extend the life of the components here and I really don't know what the actual true answer is. Both the taut-and-move-with-pressure and the sagging versions showed up in some of the "pro"pages showing up in my search. So I need to ask the people who REALLY know, you guys!
    Thanks a lot.

  2. #2
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    This was recently discussed.

    http://forums.mtbr.com/showthread.php?t=628783

    But no, there shouldn't be a 1/2" sag. Get something like a Surly Tuggnut if you're having wheel slip issues.

  3. #3
    local trails rider
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    Not so tight that it loads the bearings, but tight enough that the chain is not falling off. 1/2" when you push the chain lightly with a finger sounds reasonable to me.

  4. #4
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    if i grab my chain at the middle, between the cranks and the cog, it only moves up/down about 1in. i've found that to be the best tension for me. it's tight enough to never have to worry about a dropped chain, but still loose enough to not bind. i backspin the cranks to verify the chain is not too tight. if it doesn't freely backspin at least 1.5 revolutions (you have to put some kick into it though), then the chain is too tight.

  5. #5
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    Thanks everyone. So, a snug feel to the chain is what I am looking for, is what you're saying? It feels like there is SOME elastic tension in it, and I can displace it through this elastic tension. Does this age or wear the chain in time more than a more slack set-up? I will try the backspin test Alex suggested tonight and see.
    The tuggnut also seems like a good solution to keep that wheel in place. Are those used in pairs, on both sides, or just one?

  6. #6
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    you only need it on the drive side, but many people use one on both sides.

  7. #7
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    Quote Originally Posted by alexrex20
    you only need it on the drive side, but many people use one on both sides.
    With disks - it's a smart move to have one on both sides.
    "It's better to regret something you HAVE done, than something you haven't..." -

  8. #8
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    ya, because there's so much loading on the non drive side of the hub.

  9. #9
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    Quote Originally Posted by glenzx
    With disks - it's a smart move to have one on both sides.
    Also recently discussed, even with discs, tuggnut won't help. Disc creep makes the wheel slip BACKWARDS.

  10. #10
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    mmm, I'm worried about becoming a bit obsessed with this
    So, on the backspin test, I easily get about 2 revolutions (at least 1.5) with a moderate kick (I don't have to put all the force in when I propel it). With real effort it goes more than 2.
    However, on test spinning while in a stand, there is a bit of a ratchet feeling on the backspin. I spoke too soon about the true round of the sprockets - there is definitely an area of higher tension there. In this area of max tension the spin move is ratchety. I actually felt a bit of that ratchet move while pedaling last time I was out on it. The chain displacement in this area is only about 1/4 inch. Goes to 1/2 inch in the looser areas.
    So, should I slacken it a bit? Is the slackening something that happens with use anyway, so should I not even worry about it?
    Any further advice will be appreciated.
    Thanks

  11. #11
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    don't even worry about it. many say 1/4in chain displacement is ideal. others say 1/2in. if that is your range, then it sounds like you're good to go.

  12. #12
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    I couldn't help, the tinkerer in me was restless. I loosened the nuts and moved the wheel ever so slightly forward. It feels better! I still get a bit of a ratchety feel on part of the revolution, but most of it feels a bit better. I now get a good half inch on the looser parts, without it coming off the cogs I think, I get about 3 revolutions of backward spin with a good kick with the bike in a stand, and it just "feels" a bit easier. Now I will have to get a ruler and check the alignment of the sprockets, as I feel some of the unequal tension may have to do with them being slightly off axis (ie the freewheel, thus the rear wheel, a bit off the axis of the crank wheel, that's the only one I can fix as far as I'm concerned). I'll take it for a ride tonight see what I accomplished. If you don't see any more updates, I loosened it too much, fell off and died. But hopefully that won't be the case.
    If nothing else, going through the process was a great exercise.
    Incidentally, how tight do you tighten those nuts when you put the wheel back?

  13. #13
    local trails rider
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    Sheldon Brown (RIP) has a trick for getting chain tension more even:
    http://www.sheldonbrown.com/fixed.html#tension

  14. #14
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    Thanks perttime, I read that. The problem was, I felt a bit self-conscious about the need to ask this: What exactly are the "stack bolts"? Or the "spider" he mentions? Sorry, did I mention the noob part?

  15. #15
    local trails rider
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    He means the chainring bolts that attach the chainring to the cranks. And "spider" is the part of cranks that the chainring attaches to.

  16. #16
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    Thank you!

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