SS variable chain tension

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  • SS variable chain tension
  • trickydisco
    Member

    What’s this all about then?

    I spin the cranks around on my new SS build and at certain points the chain tension changes to tight/less tight

    Does it mean my chain ring or cog is oval?

    I’m running a 32:16 using a middleburn Uno and a surly cog at the back

    Premier Icon simon1975
    Subscriber

    Or the BB is bent, or the freehub doesn’t run straight… Try to not worry about it unless it’s really really bad!

    Premier Icon wwaswas
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    tricky – on most cransets you can adjust the chainring position so that any slight ovalness is taken account of and the tension is even.

    Clearly an Uno isn’t going to allow that.

    might be worth getting some callipers and measuring the ring to centre distance in various places plus the same with the cog?

    not sure what you could adjust to compensate if it is out though.

    trickydisco
    Member

    The BB is a lovely crank brothers ti (with 5 year warranty). Ruddy thing has always creaked.

    I’m using a normal freehub with those velospacers

    Frame is a voodoo D-jab so uses sliding dropouts

    clubber
    Member

    Pretty much all SS setups have this to some extent. You can do all sorts of ‘loosen bolts/hit with a rubber hammer’ type thing to it but I never bother – just tension in the tightest spot.

    Premier Icon wwaswas
    Subscriber

    what clubber said really, I guess – as long as it’s not so slack at the ‘slack point’ that the chain can come off you’ll be ok.

    Premier Icon firestarter
    Subscriber

    this isnt possible with the uno clubber

    trickydisco
    Member

    Cheers ppl.

    Was just worried something was pretty wrong with the setup. How much tension should i have?

    clubber
    Member

    firestarter – Member
    this isnt possible with the uno clubber

    Well if you will use a silly SS-specific chainset that doesn’t allow for one of the few adjustments a SS could use then I have no sympathy 😉

    clubber
    Member

    How much tension should i have?

    Just enough to prevent the chain dropping off 🙂

    About 1/2″ total movement in the middle of the chain run while in the tighest spot is a decent target. It’ll work much looser than that usually if your chainline is good.

    Premier Icon wwaswas
    Subscriber

    I tend to go with a bit of slack at tightest point and as long as the freehub doesn’t bind and start turning the wheel when you turn the cranks backwards as a start point.

    konaboy2275
    Member

    I’ve just returned a superstar components sprocket which wasn’t central on the freewheel (ie. the hole wasn’t centred on the sprocket). Causing a similar problem and throwing the chain all the time.

    Premier Icon epicyclo
    Subscriber

    It’s not likely the Uno is oval IME, but nothing is perfect.

    It is possible you have a slightly bent BB spindle though. Crank Bros products are prettier than they perform.

    Premier Icon Haze
    Subscriber

    Axle not being square in sliding drop-outs might also contribute…

    Premier Icon ir_bandito
    Subscriber

    Most likely your chainring is eccentric on your cranks,
    Sheldon Brown has a good method for balancing it out:

    1. Position wheel and cranks so chain is at its most taut.
    2. Loosen chainring bolts slightly.
    3. Hit chain with a hammer, so it’ll go slack.
    4. Spin cranks round and repeatedly hit the chain unitl its the same slack/tautness all the way round.
    5. Tighten chainring bolts, tighten chain.

    Job done.

    I did exaclty the same thing on my D-Jab last night

    Premier Icon wwaswas
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    ir-bandito – the uno is a combined spider and chainring – there’s nothing that can be loosened.

    Actually I had this with a Middleburn spider on XTR cranks. Thought it was the BB axle but a new BB proved no better.

    Good job its British Engineering eh?

    soobalias
    Member

    *googles middleburn uno*
    *recommends other posters do likewise*

    so i guess that only leaves the BB or rear wheel, something isnt straight. How tight is tight? are you just being over picky?

    Premier Icon ir_bandito
    Subscriber

    ah. that’s a bit of a sh!tter then.
    I guess the next possibilty is the cog is eccentric on the hub. and I’ve not got a clue waht you can do about that.

    trickydisco
    Member

    Probably being picky. I moved the dropouts further in because it was crazy tight.

    There’s no chance of the chain falling off

    I’m just a bit of a perfectionist. I’ll get the expert tollah to look at it when i see him next

    69er
    Member

    Strange one this. My fixed road bike set up has a tight spot. Don’t like it but it’s not a major issue.

    My UNO/Royce bb/Surly MTB set up is amazingly free. No tight spots and minmal friction. Engineering loveliness.

    I would suspect the parts in this order:

    Chainring (you’re stuffed!)
    Sprocket (try another?)
    BB axle
    Rear freehub
    Cranks (you’re stuffed!)

    Keep us posted!

    Premier Icon postierich
    Subscriber

    Thouht it was just chain slack, as the bottam of the chain is under less pressure than the top!!

    Then again I dont have the problem using WI freewheels just the cog spacer kits.

    mattsccm
    Member

    If you don’t sort it you could use old style CX chain guides either side of the sprocket. I find when mine gets loose and drops off it stays on the freewheel ok until the chain is right off. Its bouncing of the chain wheel. Chain gides do stop this to a great extent.

    Mmmmm… nice suggestion Matt! I’m hoping I can sort my chain dropping by replacing the SRAM chain, but a couple of guides wouldn’t hurt and would look cool as well 8)

    Premier Icon epicyclo
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    13thfloormonk – Member
    …I’m hoping I can sort my chain dropping by replacing the SRAM chain

    You’re not using a derailleur chain by any chance? Their strong selling point is that they are designed to drop off sprockets easily (rely on the derailleurs to keep them in place).

    Nah, a 1/8th PC1. Still dubious as to whats causing it, if a KMC 1/8th chain doesn’t sort it I’ll go KMC 3/32

    69er
    Member

    I had many issues with a 1/8th set up, including the chain jumping off under load.

    Since swapped to a SRAM 3/32 chain, UNO, Surly and it’s flawless.

    Hmm… sorry for the resurrection, just been out today with my new 1/8th KMC chain, and it was perfect. Actually slackened off a bit over the ride, maybe just bedding in or maybe not as stretchproof as they claim, but either way, it didn’t drop once, and the SRAM PC-1 would have been off countless times the way I was riding today.

    Obviously not conclusive in light of 69er’s ^ post, but I’ll be sticking to KMC from now on!

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