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  1. #1
    The Ancient One
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    A discussion from the Shocks page

    I thought I'd reproduce this discussion from the Shocks and Suspension forum:



    --------------------------------------------------------------------------------


    Originally Posted by mobile chernobyl
    Steve from JH - "First, the axle path is indeed very close to straight vertical. After an initial slight backward movement, the path straightens out and goes almost exactly straight up."
    "I'm not sure about the leverage ratio curve on the Equilink. The Linkage software program that many of us have won't deal with a six bar linkage."

    The verticle axle path myth that was created by specialized for marketing (any given FSR does not even have a "vertical axle path") does not hold water in the no pedal feedback argument. sorry -> vertical path = chaingrowth = feedback. Of course a concentric path is not always the answer either so dont counter me with that arguement.

    It's true that the Specialized claim of vertical axle path is BS. As I pointed out to a Specialized salesman not long ago, if you moved the rear pivot from the chain stay to the seat stay you would actually have a straighter (less sharply curved) axle path. But the Felt bike's axle path really is virtually straight. I physically measured it on an actual bike, as well as creating a similar path on a six bar applet I found on an engineering site.

    While a straight up axle path will create increasing pedal feedback with travel, the bike starts out with virtually none. For any position of the axle and bottom bracket a vertical path will always produce less feedback than a partially rearward one. The only other bikes that generate enough anti-squat to stabilize the suspension under pedaling forces all have rearward paths at sag and therefore more pedal kickback.



    Speeking of numbers is the Felt a true 6 bar linkage. I can see the rear "triangle" acting like one if the links rotations are altered that much, but whos to say Felt didnt just throw that equilink in at the perfect point to match the rotation of both links tied to a solid rear triangle. alot simpler to do - but they can still go along with their marketing strategy and sell it as a "6-bar"
    What you suggest is geometrically impossible. Unless the control arms (the rocker link and short lower link) are parallel and equal in length, putting in the equilink guarantees that all matched pairs of points other than the two equilink pivots have to get farther apart or closer together with travel. In fact the two unconnected pivots at the rear of the control arms move apart with compression and together with rebound.

    That's the secret of how the Equilink works. Forward force at the axle, trying to split apart the two rear pivots creates an equal and opposite reactive tension in the equilink. Since the control arms are aligned so that there's always more tension in the equilink than forward force on the axle, the extra tension has to be balanced by downward force at the axle. This is true in all gears, even when the chain line is angled so as to pull the axle up. You get the anti-squat you need with less pedal feedback than on other designs.




    The linkage program is useless btw unless you have CADD drawings with exact pivot locations charted. If your going to argue with a linkage design done up based on a "high def jpeg" you might as well not argue at all. With alot of designs i'm sure youve noticed +/-1mm makes a huge difference somewhere in the curve. With the Felt design youd have to throw in some FEA for the flex of the rear member and determining where bars 5 and 6 are actually - if they're actually there at all.
    You're overstating the case against the Linkage program. While it's not accurate enough to actually design a bike with, it's not useless. You may not get the exact leverage ratio curve, but you can see what kind of a curve it is. Likewise you can get an approximation of how much anti-squat and how much pedal feedback you have in different linkage positions.

    If you think the flexing stays of the Virtue model cast doubt on whether it's truly a six-bar, there can be no doubt about the other two models, the Compulsion and Redemption. They have an actual pivot near the axle and they have rigid stays. So they are clearly six-bar, seven pivot systems.



    not trying to rip on steve really as that is what it would seem - but he best exemplifies the regurgitated marketing of so many company's claims. Most of the time these suspension slogans created by companys come not from the engineers that designed the frame, but from the companys marketing staff (go figure) case in point is that they may take what the engineer tells them, but they just want to sell the frame and get coin, so lets just take out the jargon and make it understandable to anyone that its revolutionary or its the best because we tweaked the axle path.

    I'm not regurgitating anything. The explanations from Felt of how the bike works have been inadequate and I've had to find my own.

    They've done much more than "tweak the axle path". They've put forth a design where the suspension automatically extends just about exactly the right amount--without depending on a rearward axle path.
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  2. #2
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    Im glad you started this thread Steve, it seems the only really intelligent
    discussion about suspension designs comes from derby (and of course dw), so
    its nice to hear another voice giving a technical explanation of a very promising alternative system. As you know from my previous posts, I am not a fan of
    pedal feedback, no matter how well integrated into the degign it is. (I owned
    a blurXC for 6 mo.) Which brings me to my question on your comments
    below. You state that :


    "While a straight up axle path will create increasing pedal feedback with travel, the bike starts out with virtually none. For any position of the axle and bottom bracket a vertical path will always produce less feedback than a partially rearward one. The only other bikes that generate enough anti-squat to stabilize the suspension under pedaling forces all have rearward paths at sag and therefore more pedal kickback."

    It seems like you're contradicting yourself a little here.
    I currently ride a classic Horst link 5" susp. (Chumba XCL, very similar in
    design to a Motolite) While I'm not sure if the axle path is 100% vertical,
    as I dont have the Linkage software, I do know from riding it for the last
    4 mos. in all kinds of terrain that there is never even the slightest
    sensation of pedal feedback coming from the suspension, even deep into
    the travel going up sharp rocky climbs in the smallest chainring/largest cog.
    (This was the biggest reason I went with the Horst link. I have continuing issues
    with my right knee due to an injury a couple years ago, riding the blurXC
    I sometimes felt it was stressing my knee a little bit due to the pedal feedback.
    This has never been an issue on the XCL.)

    Now the real reason for my post:
    Have you ridden a dw-link bike, a vpp and the Felt(equilink) and been able to
    compare through riding them the amounts of pedal feedback of one
    versus the other ?
    One caveat is you would need to do a technical granny ring climb to fully
    evaluate the pedal feedback potential for any of these designs.
    I know how the 2 FS bikes I've owned behave in this situation, one has a lot
    of chain induced anti-squat at the expense of pedal feedback, the other has
    some susp. squat (although not as bad as many other designs) and no
    pedal feedback. I've been curious about the dw and equiink balance out the
    squat vs. pedal feedback issue.

  3. #3
    The Ancient One
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    Quote Originally Posted by le_buzz
    Im glad you started this thread Steve, it seems the only really intelligent
    discussion about suspension designs comes from derby (and of course dw), so
    its nice to hear another voice giving a technical explanation of a very promising alternative system. As you know from my previous posts, I am not a fan of
    pedal feedback, no matter how well integrated into the degign it is. (I owned
    a blurXC for 6 mo.) Which brings me to my question on your comments
    below. You state that :


    "While a straight up axle path will create increasing pedal feedback with travel, the bike starts out with virtually none. For any position of the axle and bottom bracket a vertical path will always produce less feedback than a partially rearward one. The only other bikes that generate enough anti-squat to stabilize the suspension under pedaling forces all have rearward paths at sag and therefore more pedal kickback."

    It seems like you're contradicting yourself a little here.
    I currently ride a classic Horst link 5" susp. (Chumba XCL, very similar in
    design to a Motolite) While I'm not sure if the axle path is 100% vertical,
    as I dont have the Linkage software, I do know from riding it for the last
    4 mos. in all kinds of terrain that there is never even the slightest
    sensation of pedal feedback coming from the suspension, even deep into
    the travel going up sharp rocky climbs in the smallest chainring/largest cog.
    (This was the biggest reason I went with the Horst link. I have continuing issues
    with my right knee due to an injury a couple years ago, riding the blurXC
    I sometimes felt it was stressing my knee a little bit due to the pedal feedback.
    This has never been an issue on the XCL.)

    Now the real reason for my post:
    Have you ridden a dw-link bike, a vpp and the Felt(equilink) and been able to
    compare through riding them the amounts of pedal feedback of one
    versus the other ?
    One caveat is you would need to do a technical granny ring climb to fully
    evaluate the pedal feedback potential for any of these designs.
    I know how the 2 FS bikes I've owned behave in this situation, one has a lot
    of chain induced anti-squat at the expense of pedal feedback, the other has
    some susp. squat (although not as bad as many other designs) and no
    pedal feedback. I've been curious about the dw and equiink balance out the
    squat vs. pedal feedback issue.
    First, I'll give you some figures.on pedal feedback from the Linkage program. I've used the Hollowpoint MKIII and the Motolite instead of the Mojo and your Chumba because I don't have the latter two in the program. The first figure for degrees is backward rotation of the crank during 30mm of travel from sag, calculated relative to the frame. The second figure is calculated relative to the ground. The first is important for seated pedaling, The second is important for standing pedaling or for just coasting while standing on the pedals. The anti-squat percentage is figured from sag. Everything is based on 25% sag, front and back, 30mm of travel from sag, and a gear combo of 32/20.

    MKIII
    1.9 degrees 3.6 degrees 100% anti-squat

    Ellsworth Id Cali style (my bike)
    .5 degrees 2.5 degrees 50% anti-squat

    Motolite
    -.3 degrees 1.6 degrees 0% anti-squat

    Blur
    3 degrees 4.6 degrees 100% anti-squat

    On the Motolite the feedback relative to the frame is actually negative, meaning the chain slackens during compression. The low level of feedback of the Motolite stays at a constant rate throughout travel. The MKIII and Id both diminish in feedback rate with travel. And the Blur increases.

    Where would the Felt be in all this? I can't run it through Linkage, but I suspect that it would start off about like the Motolite, but because the straight path makes the feedback increase, the overall feedback after 30mm would be somewhat higher--but still quite low. Probably only in the granny and large cog combinations and deep into travel would the feedback become significant. And how often does that happen? When climbing in those gears you're not going fast enough to get real deep into travel very often because you don't hit things hard enough. When coasting downhill you should shift out of those gears. That's a good idea on any bike.

    This all shows the pattern of pedal feedback. Now the perception by the rider of pedal feedback is something else. The feedback is there and affects you and the suspension whether you're aware of it or not. Your feet have to slow down, fighting your muscular effort, if you're pedaling, and your muscular effort slows down and reduces the action of the suspension. If you're coasting and standing on the pedals, the movement of the cranks has to move your body mass. Either way the feedback makes your body act like a kind of damper and you feel more of the effect of the bumps the higher the feedback level.

    Now riders of the DW-link bikes say they feel no pedal feedback. I suspect it's because the falling rate means the maximum backward force occurs right at the beginning when you first hit the bump. Then it feels like you pedal easily through it. You feel more shock in your feet and legs than you would with a lower feedback level, but you don't recognize it as being due to feedback. That's my guess anyway.

    I haven't had a chance to demo the Mojo or any other DW link because nobody around here sells them. The guy who promised me last fall that I could thoroughly demo both the Mojo and the Felt when he reopened his shop in the spring moved to Bozeman over the winter. Another shop picked up Felt and I did get a chance to demo a Virtue III for two days.

    The short version of how the Felt feels is that if feels like a hardtail when you're riding along a rough trail with small and medium bumps. But if feels like a hardtail on a smooth trail. As Bikemagic put it, it doesn't have that "hovercraft" feel that full suspensions usually have. You don't feel like you have full suspension, but you don't feel like there are much in the way of bumps either.

    When it came to serious downhill and big hits, the absence of a Gravity Dropper, to which I am addicted, made me feel so unstable that I wasn't really able to judge the bike properly.
    "Don't criticize what you can't understand."

  4. #4
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    Quote Originally Posted by Steve from JH
    First, I'll give you some figures.on pedal feedback from the Linkage program. I've used the Hollowpoint MKIII and the Motolite instead of the Mojo and your Chumba because I don't have the latter two in the program. The first figure for degrees is backward rotation of the crank during 30mm of travel from sag, calculated relative to the frame. The second figure is calculated relative to the ground. The first is important for seated pedaling, The second is important for standing pedaling or for just coasting while standing on the pedals. The anti-squat percentage is figured from sag. Everything is based on 25% sag, front and back, 30mm of travel from sag, and a gear combo of 32/20.

    MKIII
    1.9 degrees 3.6 degrees 100% anti-squat

    Ellsworth Id Cali style (my bike)
    .5 degrees 2.5 degrees 50% anti-squat

    Motolite
    -.3 degrees 1.6 degrees 0% anti-squat

    Blur
    3 degrees 4.6 degrees 100% anti-squat

    On the Motolite the feedback relative to the frame is actually negative, meaning the chain slackens during compression. The low level of feedback of the Motolite stays at a constant rate throughout travel. The MKIII and Id both diminish in feedback rate with travel. And the Blur increases.

    Where would the Felt be in all this? I can't run it through Linkage, but I suspect that it would start off about like the Motolite, but because the straight path makes the feedback increase, the overall feedback after 30mm would be somewhat higher--but still quite low. Probably only in the granny and large cog combinations and deep into travel would the feedback become significant. And how often does that happen? When climbing in those gears you're not going fast enough to get real deep into travel very often because you don't hit things hard enough. When coasting downhill you should shift out of those gears. That's a good idea on any bike.

    This all shows the pattern of pedal feedback. Now the perception by the rider of pedal feedback is something else. The feedback is there and affects you and the suspension whether you're aware of it or not. Your feet have to slow down, fighting your muscular effort, if you're pedaling, and your muscular effort slows down and reduces the action of the suspension. If you're coasting and standing on the pedals, the movement of the cranks has to move your body mass. Either way the feedback makes your body act like a kind of damper and you feel more of the effect of the bumps the higher the feedback level.

    Now riders of the DW-link bikes say they feel no pedal feedback. I suspect it's because the falling rate means the maximum backward force occurs right at the beginning when you first hit the bump. Then it feels like you pedal easily through it. You feel more shock in your feet and legs than you would with a lower feedback level, but you don't recognize it as being due to feedback. That's my guess anyway.

    I haven't had a chance to demo the Mojo or any other DW link because nobody around here sells them. The guy who promised me last fall that I could thoroughly demo both the Mojo and the Felt when he reopened his shop in the spring moved to Bozeman over the winter. Another shop picked up Felt and I did get a chance to demo a Virtue III for two days.

    The short version of how the Felt feels is that if feels like a hardtail when you're riding along a rough trail with small and medium bumps. But if feels like a hardtail on a smooth trail. As Bikemagic put it, it doesn't have that "hovercraft" feel that full suspensions usually have. You don't feel like you have full suspension, but you don't feel like there are much in the way of bumps either.

    When it came to serious downhill and big hits, the absence of a Gravity Dropper, to which I am addicted, made me feel so unstable that I wasn't really able to judge the bike properly.
    Those figures for the Motolite are a little surprising, as far as the 0% anti-squat.
    When did the version of Linkage that youre using come out ?
    The reason I ask is that there was an earlier version of the Motolite that had
    an FSR like rear end configuration before they changed it to the current strut
    based configuration. The strut based configuration is supposed to have a mild
    degree of anti-squat. Also, if youre Linkage sofrware is older than '05, chances
    are its using the second generation dw-link for the Hollowpoint mkiii stats,
    although this probably not make a big difference in so far as the pedal feedback
    numbers.

    Another thing is I think you would get figures that more reflect the amount of
    feedback that a rider feels if you used a 22/20 gear combo instead.
    On my blurXC this combo produced the most pedal feedback. In the 32/20
    combo it was still there, but much less perceptable, probably more link the
    dw-link.
    I would be curious how they rate the Turner and FSR Horst link bikes as
    far as the anti-squat.
    I think you may have hit onto something as to your explanation of why
    dw-link riders claim they feel no pedal feedback. I suspect the spike occurs
    at a different spot during the pedal stroke than on the vpp's, thus masking it
    better. With my blur the spike appeared to occur at the top of my pedal stroke,
    where you would notice it more. In the middle ring it was much less
    noticeable, only slightly noticeable, but still there.

  5. #5
    The Ancient One
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    Quote Originally Posted by le_buzz
    Those figures for the Motolite are a little surprising, as far as the 0% anti-squat.
    When did the version of Linkage that youre using come out ?
    The reason I ask is that there was an earlier version of the Motolite that had
    an FSR like rear end configuration before they changed it to the current strut
    based configuration. The strut based configuration is supposed to have a mild
    degree of anti-squat. Also, if youre Linkage sofrware is older than '05, chances
    are its using the second generation dw-link for the Hollowpoint mkiii stats,
    although this probably not make a big difference in so far as the pedal feedback
    numbers.

    Another thing is I think you would get figures that more reflect the amount of
    feedback that a rider feels if you used a 22/20 gear combo instead.
    On my blurXC this combo produced the most pedal feedback. In the 32/20
    combo it was still there, but much less perceptable, probably more link the
    dw-link.
    I would be curious how they rate the Turner and FSR Horst link bikes as
    far as the anti-squat.
    I think you may have hit onto something as to your explanation of why
    dw-link riders claim they feel no pedal feedback. I suspect the spike occurs
    at a different spot during the pedal stroke than on the vpp's, thus masking it
    better. With my blur the spike appeared to occur at the top of my pedal stroke,
    where you would notice it more. In the middle ring it was much less
    noticeable, only slightly noticeable, but still there.
    Sorry I didn't get back to you sooner.

    This time I'll give you the same set of figures from the Linkage program, but with a 22/34 gear combo. This lowest gear will have both the most feedback and anti-squat. I'll be using the Mojo, as put into the program by Derby, and the Motolite (in its more recent configuration, which is what I used before) put into the program by Antonio Osuma, one of the original Linkage guys. The Id was put in by me. And the Blur is from 2006, put in by Gwyn Taverne Smith, who I don't know.

    Once again the order of the numbers is: feedback relative to frame (seated pedaling), feedback relative to ground (seated pedaling or standing on pedals), anti-squat percentage (based on a center of mass height of one meter).

    Mojo
    6.8 degrees 7.4 degrees 121%

    Id
    3.6 degrees 6 degrees 100%

    Motolite
    1.7 degrees 3.2 degrees 55%

    Blur
    8.2 degrees 9.9 degrees 126%

    Without looking them up, because I'm tired, I'd say that the Specialized FSR's will be similar to the Motolite. And I know the Turner Horst 5-Spot is very close to the Id.
    Last edited by Steve from JH; 11-02-2007 at 11:09 AM.
    "Don't criticize what you can't understand."

  6. #6
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    Those squat numbers seem a bit high to me. Are you sure the way youre measuring it, or the parameters youre putting into Linkage, are accurately
    reflecting a real world situation ? The one Im most suspicious of is the Id.
    You may be aware of this already, but one of the developers of Linkage
    exposes the fallacy of Tony Ellsworth's arguments about ICT, insofar as
    his claims of 100% antisquat, anyway.
    I can tell you for sure that the 5-spot is not going to have anything close
    to 100% antisquat, whether its HL or TnT version. My portly Chumba XCL
    should have more antisquat than the spot, which has a fair amount of bob
    from what I've read.

  7. #7
    The Ancient One
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    Quote Originally Posted by le_buzz
    Those squat numbers seem a bit high to me. Are you sure the way youre measuring it, or the parameters youre putting into Linkage, are accurately
    reflecting a real world situation ? The one Im most suspicious of is the Id.
    You may be aware of this already, but one of the developers of Linkage
    exposes the fallacy of Tony Ellsworth's arguments about ICT, insofar as
    his claims of 100% antisquat, anyway.
    I can tell you for sure that the 5-spot is not going to have anything close
    to 100% antisquat, whether its HL or TnT version. My portly Chumba XCL
    should have more antisquat than the spot, which has a fair amount of bob
    from what I've read.
    The measurements I'm most sure of are for the Id, since it's my bike. I can compare the measurements shown in the program to the actual measurements taken on the bike and correct them and that's what I've done.

    Like a lot of people, Ken Sasaki has a thing against Ellsworth. Ellsworth's claims are not fraudulent or bogus or marketing BS, they're just mistaken. They're based on an old-fashioned way of looking at suspension, without reference to more recent engineering texts on motorcycle chain drive dynamics.

    By the way, Ellsworth does not claim 100% anti-squat (measured in the middle ring, middle cog--where ICT is literally true). He claims something like 25% or 30%. That's wrong for the Id, because of the old fashioned way he measures it. It's 50% in that gear combo, as I said in my earlier post. It goes up to 100% or close to it in the low 22/34 combo. Just as the Motolite goes from 0% to 55%.

    The 5-Spot is very close to the Id.

    I'll stand behind the at least approximate accuracy of these figures.

    Below I've attached a diagam and derivation for percentage of anti-squat that I prepared some time ago. It's highly technical, but if you understand the basic concept of torques or moments and if you know the trigonometric functions, you should be able to puzzle through with time.
    Attached Images Attached Images
    "Don't criticize what you can't understand."

  8. #8
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    Do mind if get derby to chime in on this ? I think I remember the basic trig fcns.
    but putting that whole thing together without my college math books for
    reference is a bit daunting for me. Plus, as obfuscating as his posts can sometimes seem, I think two opinions are always better than one.
    (of course, we're risking having this thread moved back to the shocks forum, but
    thats an issue for the moderators)

  9. #9
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    Let me tell you this, I own a Moto Lite and have had the oppurtunity to demo a 07 Vrtue Two and have found (IMO) the Felt to be a MUCH better pedaller. And that was with a Float R without Pro-pedal and other fancy settings at the back. The ML is more plush, but if you're looking for somthing with travel that can pedal like hell...ssad to say but the Felt is it.

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