Do oval chainrings disrupt anti-squat?- Mtbr.com
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  1. #1
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    Do oval chainrings disrupt anti-squat?

    After reading an article recently where the reviewer noted that he thought he was experiencing a negative impact in the anti-squat of the suspension due to the oval chainring.

    Of course on my next ride I thought I was feeling some weirdness while pedaling.

    Based on suspension kinematics is there any drawback to running an oval on a full suspension bike?

    (bike in question is the new Kona Process 134 29er with a 30t oval)

    Edit: To clarify, the bike being reviewed was not the Process, My bike is the Process and I'm wondering if it could be negatively impacted by an oval?
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  2. #2
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    Quote Originally Posted by *OneSpeed* View Post
    After reading an article recently where the reviewer noted that he thought he was experiencing a negative impact in the anti-squat of the suspension due to the oval chainring.

    Of course on my next ride I thought I was feeling some weirdness while pedaling.

    Based on suspension kinematics is there any drawback to running an oval on a full suspension bike?

    (bike in question is the new Kona Process 134 29er with a 30t oval)
    Wow. Coincidentally, I just read the exact same review. Super controversial review start to finish, including the oval ring thing.
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  3. #3
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    Often wondered this as well but can't say I notice anything running ovals.
    Link to review?

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  5. #5
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    Quote Originally Posted by mtnbkrmike View Post
    Wow. Coincidentally, I just read the exact same review. Super controversial review start to finish, including the oval ring thing.
    Quote Originally Posted by Suns_PSD View Post
    Often wondered this as well but can't say I notice anything running ovals.
    Link to review?
    I don't want to go OT, the article is not the question. The question is do oval chainrings disrupt anti-squat?
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  6. #6
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    EDIT: NVM.

    I will wait for smarter folk than me to chime in.

    I have to think it impacts it to some degree. The issue is whether it is material enough to "disrupt" AS.
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  7. #7
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    Quote Originally Posted by mtnbkrmike View Post
    Do oval chain-rings disrupt anti-squat?

    I know of no principled basis to suggest that they would not at least impact it. Watching the chainline vary as I slowly pedal my Honzo in the stand (which has a RaceFace oval ring), the repetitive impact appears clear. The issue in my mind is whether that impact is material.
    Right, the question only applies to full suspension bikes. I've used many ovals on many hardtails both SS and geared. This is my first oval on a FS bike.

    Hoping to get some feedback from people who have a good understanding of suspension kinematics.
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  8. #8
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    Quote Originally Posted by *OneSpeed* View Post
    Right, the question only applies to full suspension bikes. I've used many ovals on many hardtails both SS and geared. This is my first oval on a FS bike.

    Hoping to get some feedback from people who have a good understanding of suspension kinematics.
    Sorry about that. I will sit back, read and learn
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  9. #9
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    I was actually JUST thinking this today, reflecting on my ride on Wednesday. It was the first ride with a 30t OneUp oval ring and it felt funny. I had a 32t round ring on Monday when I rode and that felt pretty good. I have a 32t round Oneup ring on the way for my XTR crankset, and I intend to compare them one after the other on the trail!

    As for does it "disrupt" as, i can't say, but it does change as depending on where the chain is on the oval. If we look at a 10t difference on an example bike, the change is about 2.5% per tooth in a climbing gear.



    Distance from center to bottom of chain on my bike

    32t round: 60mm
    30t oval max: 63mm
    30t oval min: 55mm

    So the as will change a bit depending on where the oval is in the stroke. But on the other hand, the chain tension is changing and should be less at higher as positions.

  10. #10
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    "Disrupt" is the wrong word. Antisquat is calculated by plotting the various suspension characteristics (instant center) throughout its travel. An oval chainring does change how torque is applied to the cassette, which means that antisquat would have to be plotted as a range for every point in the travel. But suspension is not a static thing, all antisquat ever was telling you was one characteristic at a static point. Just as changing gears and moving the suspension changes the suspension performance, this just introduces one more variable. Ultimately, the chain pulling on the suspension has effects, and we can plot/model those effects, but viewing this as a static thing is really an oversimplification. An oval chain ring doesn't "disrupt" antisquat any more than changing the pivot points "disrupt" antisquat.

  11. #11
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    Plotting the function of how a.s. changes through travel with changes in crank position with the changing force on the chain, over time, would be a chore. The linkage software also costs money and I haven't decided if I care enough about this to spend it. I think Excel could do the rest. If I had a youtube channel and could turn this into clicks and ad revenue I might do it. But for now I'm going by feel.

  12. #12
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    Quote Originally Posted by mtnbkrmike View Post
    ...I will wait for smarter folk than me to chime in...
    OK. I'll chime in.

    The way I see it: Anti squat matters when you are pushing hard on a pedal. That happens over about 90-100 degrees of pedal stroke on each side. It's the effective diameter of the chainring during the main part of the power stroke that will determine anti squat. Typically, an oval will be phased such that it has the largest effective diameter during the main part of the power stroke, so that will determine the effective anti squat for the oval. A 30 tooth oval that has an effective range of 28-32 teeth, will have basically same effective anti squat as a 32 tooth ring.
    Do the math.

  13. #13
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    It's not going to have a big effect, if you look at the changes for difference sized chainrings, it's usually a % change in the single-digits.

    The "hump" is likely going to lower AS, as it simulates having a larger chainring. This will cause the suspension to "squat" more uphill under power, but this wouldn't be like the sustained issue with a low-AS bike like a horst-link that has a falling AS curve through the travel, where you kind of get into a feedback loop of falling further into the travel where there is less AS that lets the suspension compress more and lightens the front end, causing pedaling torque to further compress the suspension. If anything, on these kinds of bikes, an oval chainring may slightly exaggerate this, but again, it's only a couple percentage points, so I can't imagine this being something that could be discerned. If anything, you'll notice the impulse of power more IMO. On other bikes that don't have excessively low/falling AS, as soon as you are past the "hump" you are "back" to the higher AS, I think everything considered, there are other factors that will affect AS just as much, like weight placement. The AS assumes placement of weight on the bike in a certain range, but it varies from rider to rider and situation to situation, so the amount of AS needed varies and the AS numbers generated from computers are only static situations. Stuff is moving around more anyways while riding and I doubt this makes any discernible difference.
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  14. #14
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    ^ Cool. I know the effect would be small but there's a couple other factors I'm curious about.

    Would standing and climbing exaggerate the impact? I stand a lot and that's when I thought I noticed it most.

    Instead of "disrupt" you could substitute "negatively impact" or cause it to feel funny.

    Thanks for the replies.
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    There isnít any negative effect as squat is the response to acceleration, and the phase of oval chainrings is such that acceleration is less at the same point that the anti-squat is reduced, ie the major-axis of the chainring is at the top or feet around 12 or 6 o clock

    So the effects balance out

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    Quote Originally Posted by JohnnyC7 View Post
    There isnít any negative effect as squat is the response to acceleration, and the phase of oval chainrings is such that acceleration is less at the same point that the anti-squat is reduced, ie the major-axis of the chainring is at the top or feet around 12 or 6 o clock

    So the effects balance out
    Cool, thanks. So since my bike won't explode I should just continue to ride it?
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  17. #17
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    I never felt such effect with my oval CR. If there's variation on the AS (as there is depending on a number of factors others already said, such as stroke of suspension and rear cog), it's pretty much damped by the smoother power delivery (you'd get more squat at the same time your power to the chain decreases).

    Anyway, best way to find if this is a problem for you is trying for yourself. Different setups with different ride styles will cause different effects.

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