Adding idler pulley to reduce anti squat and pedal kickback?- Mtbr.com
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  1. #1
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    Adding idler pulley to reduce anti squat and pedal kickback?

    Anti squat can be reduced by increasing the chainring size, a larger diameter chainring will pull less on the chain. So if we would add an idler pulley above the chainring, we could decrease anti squat, and reduce pedal kickback right?

    High pivot bikes use an idler pulley, because of the rearward axle path, but can it be usefull on different suspension design?

    Norco used a DIY idler pulley a while back on the aurum.

    Not all bikes have space to make something like this, but on some you could use the iscg tabs to fabricate something to position an idler pulley on the desired spot. A chain device could be modified perhaps.

    So to all the suspension guru's, does my theory sounds about right?
    Will this reduce pedalkickback, will it still be pedalable, any problems i might have forgotten?

  2. #2
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    Yeah. Larger chain ring or larger cog both reduce anti squat. Going from 28f/42r to 32f/50r will make a significant diff. Adding an idler to an existing frame would be complicated, I imagine. What bikes would need that much of a change?
    Do the math.

  3. #3
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    Simply put, that is correct

    you will need to calculate things very carefully though so it doesn’t go complete out of whack. A few things to consider-

    The chain puts a ton of force through an idler and the sharper the bend the more force it applies. A chainguide arm will not be strong enough and I would aim for as direct a mount as possible

    It can be hella noisy, but a larger cog is quieter than a small one

    It will need some kind of retention to keep the chain on but not jam

  4. #4
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    A buddy of mine is all about the idlers on his FS frames.
    Sticks them right at the pivot point.

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  5. #5
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    Why do you want to reduce anti squat?

  6. #6
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    While it could work and reduce kickback in theory, I can think of a lot of potential pitfalls and negative side effects and you'd still be stuck with the same axle path. What bike are you looking to add an idler to? Why not get a bike with suspension that's actually designed around a high pivot and idler or even just another frame with lower anti-squat?

  7. #7
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    Both of my bikes have pretty high AS values, my orbea rallon has one of the highest as values of the recent enduro bikes, and allthough i really cant complain on how the rallon descents( awsome geo) i do feel a bit less pedal kickback would be better. I switched to a 34 chainring and felt a very small improvement. My legs dont have the power to move up to a 36. I would rather go back to a 32 and add a small pulley that corresponds to the height of a 36t or 38t chainring. I have an old mrp chainguide that is pretty stout, seems it wouldnt flex. The lower pulley has the same mounting as the upper guide, i think it could work as a idler pulley.

    https://imgur.com/4SC3azD

    My other bike is a canyon sender AL, but the chainstays are lower than the rallons and it Will be harder to make it work imo.

  8. #8
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    Chain tension can be pretty high so an idler would have to be strongly mounted. If you weight 170 lbs and put all your weight on a 170mm crank arm with a 32 ring, that's 445lb tension in the chain.
    Do the math.

  9. #9
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    IMO, harshness deep in the travel on modern bikes is more a function of air shocks (too progressive and stiction) and ill-suited damping tunes. Using a coil on “high AS” designs, it’s usually a paradigm shift in compliance, suppleness and bump absorption.

    This excludes the wonky 150%+ AS designs without falling-rate AS.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  10. #10
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    ^^^ As I understand it, the leverage curve and AS/kickback are more or less independent.
    Do the math.

  11. #11
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    I doubt you're really feeling kickback on the descents, unless maybe you have a super high or infinite engagement hub (e.g. Hydra, Onyx)?

    I've got an Intense Recluse, which has even more anti-squat and kickback than either of your bikes. I've found that pedal kickback is generally most noticeable at slow speeds in low gears. I mostly feel the kickback when trying pedal over chunky rocks or roots. I do feel it when pedaling in higher gears as well, but it's not nearly as bad and I don't often try to pedal through thick chunk when I'm at the top end of my cassette anyway. When coasting, the freehub is not engaged and I don't think I feel much if any kickback.

    If you're feeling harshness through the pedals on the descents, my guess is it has more to do with your rear suspension setup than pedal kickback. Going from the stock Fox DPS to a DB Coil IL on my Intense made a massive improvement in plushness to the point where the rear end now out performs the Pike up front (and probably any fork I've ever ridden, although I haven't tried a coil fork yet) even with that high anti-squat.
    Last edited by dlxah; 10-08-2019 at 10:12 AM.

  12. #12
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    The pedalkickback you discribe, when climbing, i am familiar with, dont really notice it much on the rallon. I allready have a DHX2 coil on the bike, setup pretty good. I have ordered the new 2020 year linkage for the rallon, that should help the initial sensitivity, but like someone here said, i dont think AS and pedal kickback is related to the leverage curve.

    I once broke a chain and finished the descent, and i must say that it was alot more plush and probably the feeling i discribed as no pedal kickback( du’h)

  13. #13
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    Quote Originally Posted by Sigmo View Post
    The pedalkickback you discribe, when climbing, i am familiar with, dont really notice it much on the rallon. I allready have a DHX2 coil on the bike, setup pretty good. I have ordered the new 2020 year linkage for the rallon, that should help the initial sensitivity, but like someone here said, i dont think AS and pedal kickback is related to the leverage curve.
    Yeah, the stock link on those bikes looks too linear to work well with a coil. I wonder if maybe the problem is you're having to compensate for that with a very firm spring rate or excessive damping. The new leverage curve does look like it should work a lot better for you. The new link actually should reduce the anti-squat by maybe a few percent too, since it lowers the rear end and moves you a bit further down the anti-squat curve.

    Quote Originally Posted by Sigmo View Post
    I once broke a chain and finished the descent, and i must say that it was alot more plush and probably the feeling i discribed as no pedal kickback( du’h)
    Interesting. Out of curiosity, what rear hub are you running on that bike? Did the chain break while pedaling or coasting?
    Last edited by dlxah; 10-08-2019 at 10:12 AM.

  14. #14
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    Quote Originally Posted by Lone Rager View Post
    ^^^ As I understand it, the leverage curve and AS/kickback are more or less independent.
    I think the other big contributor to this is the falling-AS-curve bikes get into a feedback loop that makes them use more travel on uphill tech obstacles than they'd use when coasting over the same object on level or downhill. As you encounter a bump, it puts the travel to where there's even less AS, you naturally slow down, so you pedal more to overcome it, but that shifts more weight rearward and due to the already low AS, it makes more of that pedal stroke compress the rear end, rather than make you go forward, making the front lighter, making you have to pedal harder to keep going forward and kind of getting in a "feedback" cycle. When you ride a bike that uses "about the same" amount of travel uphill and downhill, it feels much more like it rides "above" the rocks, rather than "digging into" them. Sometimes, this is characterized as "pedal kickback", when the bike doesn't have that real soggy "digging-in" feeling that the low-AS bike has.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  15. #15
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    I have DT240s hubs, i think with 36 POE.

    I will evaluate again when i install the new linkage, maybe try the modified pulley device, if i have time to make it if its reversible it doesnt matter if it wont work like i thought it would

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