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Thread: Fixed gear chain tension

  1. #1
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    Default Fixed gear chain tension

    I changed the tires on my fixed gear last night and today the chain was definitely a lot looser than it had been. I thought I had pulled it pretty tight but apparently not.

    Is there a guideline for how tight it should be, or is it more "you know it when you ride it" or "just get it really tight"?

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    TwoWheelsDC's Avatar
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    Droopy is too loose, but there should be about a half-inch or so of play if you grab chain at the top and move it up and down. Also, too loose is probably better than too tight, since a tight chain will damage your rear hub and cause extra resistance in the drivetrain. If you hold up the rear wheel and spin the pedals, they should spin freely and fairly quietly. Too tight and you'll notice how quickly the pedals stop and the extra noise.

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    But you want to check the play a multiple spots until you find the tight spot on the chain where there is less play and make sure that it does not bind at that spot. Just like a motorcycle.

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    Quote Originally Posted by OneEighth View Post
    But you want to check the play a multiple spots until you find the tight spot on the chain where there is less play and make sure that it does not bind at that spot. Just like a motorcycle.
    Chain rings (when mounted on a the crank) are usually slightly eccentric. One way of fixing this goes like this:

    1) set the chain tension to be no tighter than to allow 0.5" to 0.75" of vertical play in the chain, measured halfway down the chainstay
    2) loosen all the chainring bolts, but not loose enough that the chainring becomes loose - about 1/2 to a single turn on each bolt
    3) using the handle of a hammer, and while turning the cranks, tap the chain mid-chainstay
    4) you'll see where the eccentricity of the chainring/crank is because the chain play will decrease as you spin the cranks - tap the chain when it tightens to pull the chainring closer to the rear hub
    5) once you've centered the chainring on the crank (i.e. chain play is constant through an entire pedal stroke) retighten the chainring bolts and double check the chain tension by moving the hub in the dropouts

    One other trick is to walk the hub backward in the dropouts by only pulling the wheel towards the driveside/nondriveside at a time. for example, loosen the driveside hub nut and grab the rim near the chainstay, pulling it towards the chainstay. then tighten the driveside hub nut. then loosen the nondriveside hub nut and grab the rim near the nondriveside chainstay and pull it back to center between the chainstays. do this several times until there's proper chain tension and the the rim is centered between both the chainstays and seatstays.

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    Man, I thought fixed gear was supposed to be simple.

    The one side at a time thing sounds doable, though. Thanks, all, for the help.

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    Quote Originally Posted by jrenaut View Post
    Man, I thought fixed gear was supposed to be simple.

    The one side at a time thing sounds doable, though. Thanks, all, for the help.
    honestly, the only time i ever really worry about chainring eccentricity is on actual track bikes (that are actually going to be raced on a track), and it's more for smooth pedal feel through the pedals than anything else. wonky chainrings are noticeable at high power/high cadence. on anything else fixed-gear, leaving the chain on the looser side if things will tolerate any chainring eccentricity and is a lot less hassle.

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    The "one side at a time" trick is the one I use. One thing I've found when checking fixie chain tension is that listening to the chain can be more helpful than looking at it—there's a certain sound that overtightened chains make that's pretty easy to hear, but hard to see while it's moving. Maybe it's just me, but visual cues always seem debatable and never quite clear, while getting the bike to "sound right" is much less ambiguous.

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    I never worried about slight chainring eccentricity on my fixies. Just check the tension at 90 degree rotations and make sure it isn't too tight and you should be good. The chain doesn't need to be super precisely tight. You want a small bit of play (it shouldn't be under tension on the stand). Just make sure it isn't loose enough to come off. Fixies throwing a chain is sort of unfun.

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    I noticed that mine was loose when I was slowing without the brake - there was a funny "hop" in the pedal when I was getting slack in the chain rather than slowing the bike. I'm on the cargo bike with the kids today, but hope to maybe sneak out somewhere on the fixie this weekend...

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    I go by the 0.5 to 0.75 inch loose rule although I'm not super strict on policing my bike set up regarding chainline, tension, etc (I have a dixed cog after all). I usually only look to adjust stuff if it feels/sounds off.

    Chain stretch means you'll have to pull the wheel back a bit every now and then. I do the one side at a time thing too. Both my FG + SS have fairly new chains right now so they sound pretty quiet but I did have to re-tension the FG's chain a few weeks ago.

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