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  1. #1
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    Pedal feedback: Coming full circle

    Pedal feedback: Coming full circle

    A disturbing trend seems to have reappeared on my rides lately: right knee pain (the knee I injured in a OTB crash back in '05).

    My first full susser in '06 was a blur xc. You know the story by now; backward crank tugs on granny climbs followed
    by aching knee for the next couple days. Couldn't wait to get rid of that.

    So I played it safe on my next couple bike purchases, sticking to the tried and true horst link flavors of suspension design.
    Fast forward to 2011, and I realize that I'm avoiding long climbs on my Knolly Delirium due to how winded you get when things get steep.

    But while Knolly's 4X4 may be the most efficient HL design on its face, I'm realizing that for AM riding it's just not the ticket.
    (Unless you're one of the guys featured in one of gthose North Shore videos on the Knolly site.) Still a great bike , though.
    Just not my cup of tea as an all rounder.

    While I was still leery of dual link designs due to the potential for pedal feedback (and how hard that is on your knees),
    a couple of Firebird demos that featured technical climbs without a hint of noticeable pedal feedback convinced me to give the
    Firebird a try. So I sold the delirium frame and picked up the Firebird frame a few months later.
    Everything went well at first as far as the pedal feedback goes. (Although I did have to ditch the rp23 that the bike came with
    for a DHX air to get some plushness out of it.) The DHX air started drooling oil a few months back, so I sent it back on warranty,
    and while it was there at Fox they retuned it for the Firebird spring rates and my weight- I was told - in addition to the warranty work.

    I thought, WOW, splendid and dandy, but I still wanted a bit more plushness out of it, so I've decided to go for a fox DHX RC4 coil.

    Now (finally) we get to my question: While I really want to make this mod, will going coil possibly have a negative impact on the
    overall pedal feedback issue ? The suspension was apparently designed around an air shock, which are inherently progressive.
    So would going coil help flatten out the spring rate curve a bit in the middle, perhaps lessening the overall amount of
    pedal feedback that goes into my knee ?

    I should add that while I'm not feeling the classical symptoms of pedal feedback, i.e., backward tug on the cranks, herky-jerky pedaling
    in the granny/tech, etc., I'm pretty sure my knee pain is due to the chain growth that goes along with dual link designs.

    Thanks for reading.

  2. #2
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    Sorry not quite getting the connection between pedal bob and knee pain. I can't comment on the coil, but, I'm curious about the knee pain and maybe there is a better solution. Personally I have patellar chondromalacia and have never noted any connection between sagging and knee pain, but, that means nothing because different injuries cause different mechanical limitations.

    - What exactly is your knee injury? (ACL/MCL/LCL/PCL/Patellar Chondro... )

    - Are there pending muscle/strength/stability issues from the injury? Does your physical therapist agree you're 'done'?

    - What is it about pedal bob that aggravates the knee? Is it that the bob results in sagging to a lower position? I've never had a bike sag that far under hard pedaling (that it changes the knee motion significantly). Is your sag set correctly? Have you tried going a little stiffer than the recommended sag?

    - If its not the sag/position change that bothers the knee, what is it? Are your RPMs too low on your climbing? Just the fact there is a little 'squish' during pedaling shouldn't really cause pain. Its just extra resistance at the pedal - its taking some of the force on the pedal and putting into heating shock oil instead of delivering it to the wheel. The knee doesn't 'care' whether the resistance is coming from the tire or the piston trying to move through shock oil, right? I don't see how chain growth would do it either - its just taking resistance at the pedal.

    Have you experimented with the spin-bike at the gym and seen if you can draw any relationship between resistance, RPM, position (matching your fore-aft position, and full leg extension position exactl), and knee pain? This serves as your 'control' for the experiment :P.

    - Is your seat set correctly when climbing? At the bottom of your stroke you should have only a minor ~3-5degree bend in your knee. Too low (too much bend) and knee pain is a sure result. People hate riding with their seat this high because you have to keep stopping to drop it on downhills, but its worth it. The magic of the dropper obviates this. How about fore-aft seat adjustment - have you done the plumb-bob test to make sure your knee is directly over the spindle?

    (see here: Bike Fit: Set Your Bicycle Saddle Height | Bicycling Magazine)

    - Do you use clipless? What kind? Do they have enough float? Adjustable tension?

    Regardless, to your question: I have not tried a coil on my firebird, I would think an RP23 with pro-pedal would be better for pedal feedback than a coil, because pro-pedal basically kicks up the low-speed compression with the flick of the switch, limiting pedal bob on climbs. Even then though, on my Firebird with RP23, propedal engaged, I still get some very minor pedal bob on steep seated climbs where I'm grinding at max torque.

    Some other things you might look into:
    - Shock with full lockout
    - Go 2x10 or 1x10 so that you're forcing yourself to use a higher gear, which will have less pedal bob than the granny. You can experiment with this by forcing yourself to stay in the middle ring next ride. However, careful because it could have the opposite affect, if you find yourself bogging down and hammering up those hills at low RPM in middle ring, you can really aggravate your knee.

    Hope that helps!

  3. #3
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    Quote Originally Posted by le_buzz View Post
    Pedal feedback: Coming full circle

    I'm pretty sure my knee pain is due to the chain growth that goes along with dual link designs.

    Thanks for reading.
    Part of the compromise. Just back pedal each time you hit a bump, it'll go away.
    Nice KOM, sorry about your penis.

  4. #4
    official eMpTyBRain
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    Perhaps you are trying to climb hills that are too tough on your knees? Or hills that are too steep for the Firebird? Perhaps you should reinvest on a middle grounds platform that will climb well AND descend well? Or perhaps you should just shuttle to the top?
    ...and proud member of the anti-sock puppet desolation

  5. #5
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    Thanks for the reply. I also have chrondomalatia. I already dome physucal theraspy,
    and getting all the fitting issues right. I went on a ride *shoort( today and it was fine;
    but when I walk or stand on that knee it hurts.

  6. #6
    ZEN RIDER!
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    There are some older posts on different shock options for the bird and if i remember correctly the rc4 coil.
    Personally i would have went with this
    Took my Firebird out today with the Double Barrel Air
    Life in every breath

  7. #7
    jddist
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    I had similar problems and ended up selling my bird, but a few people told me to try a different gearing up front (larger granny chain ring) and that would reduce the kickback some. Might be worth a try.

  8. #8
    Appalachian Singletrack'n
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    Though Ive never noticed pedal kickback on my bird, according to the suspension graphs on bike cad the bike has significant pedal kickback in the granny.

    my browser translates for me:

    Linkage Design: Pivot Firebird 2010

    Chain elongation is like 30mm or so near full travel. I would say my firebird climbs tech rock allot better in the middle ring if ive got the motor to keep it going. That about the only time I ever notice anything but spectacular climbing.

  9. #9
    ZEN RIDER!
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    Granny gear?! That's your problem-dont use it!
    I don't use my granny gear much at all, so I;ve never experienced any sort of feedback.
    Most of the time even after almost 2 yrs I still marvel on how well the bird pedals.
    I would also concentrate on your pedal stroke. Make sure its not herky jerky due to compensation for knee pan. just a thought.
    Life in every breath

  10. #10
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    Quote Originally Posted by Mt.Biker E View Post
    Granny gear?! That's your problem-dont use it!
    I don't use my granny gear much at all, so I;ve never experienced any sort of feedback.
    Most of the time even after almost 2 yrs I still marvel on how well the bird pedals.
    I would also concentrate on your pedal stroke. Make sure its not herky jerky due to compensation for knee pan. just a thought.
    Honestly, this sounds a little crazy but is 100% spot on. I went from a Titus ML to a Turner 5-spot and it took me a while to figure this out. On the old ML, you needed to spin, as being in too big of a gear would cause you to bob up and down like crazy. Sitting and spinning was the key. On the 5-spot, the granny does feel weird but you can stay in the middle ring and lose nothing. There will be no bob and you can even stand and hammer up the hill. Both designs work well but require different ridding techniques.

    My solution, ditch the granny.
    On MTBR, the reputation is infamous.

  11. #11
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    Quote Originally Posted by le_buzz View Post
    snip...
    I run a RC4 on my bird and I understand the exact feeling you are getting through the pedals. The RC4 in my opinion is well worth the money, weight and 'perhaps' an increase in pedal feedback (not spent enough time on air to compare).

    For me it's only a concern on more technical climbs when choosing a line and putting some power down at specific points is important. When the pedal feedback occurs the entire bike feels ungainly, for lack of a better word. It's not the same type of feedback I've experienced on other bikes.

    Strangely enough, the pedal feedback has increased dramatically after I installed a RWC upper bushing kit - the kit is awesome if you like small bump compliance and I highly recommend it, but pedal feedback has increased a lot. Perhaps a little stiction in the bushing was helping?
    Not sure If i should just run more LSC for technical climbs? would this adversely effect traction?

    For me, not using the granny is not an option, the hills are steep around here, while I could muscle up them on a 32t+ on the front, I think traction would be compromised and I'll be not having a whole lot of fun... I got old and unfit .

    I have a PhD in knee rehabilitation and I have been pondering your problem for a few days. I can't see that pedal feedback would have a significant or measurable impact on you knees. ddprocter has nicely outlined some other potential areas that may be worth investigating - particularly strength training in increase joint stability around the knee.

  12. #12
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    Wow, I just had the RWC kit installedseveral weeks ago. Incidentally, Im already running a 26
    up front, thinking of goinjg single rind=g and rc4

  13. #13
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    By the way, would the mojo hd have significantly less pedal feedbacxj

  14. #14
    ZEN RIDER!
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    If feedback is your number one priority i'd go something with less travel and not dw link(or similar small link). Ellsworth ICT perhaps and if you want travel the Moment is a capable bike that climbs wells.
    On today's ride i'm going to try granny gear, before i remove it soon, and see if i notice anything. You have me curious as to the effect your talking about.

    I was just about to order the RWC kit because i figured it will be more durable and last longer than the bushing.
    Life in every breath

  15. #15
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    A couple of questions from a semi-layman to full sussers:

    - If a larger chainring makes climbs too difficult, can you swap the cassette for something that has larger sprockets to compensate?
    - Is locking out the rear suspension for climbs an option at all?

  16. #16
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    That question depends on many variables. Type of bike and intended use.
    XC bikes typically have 3 chain rings which give you lots of gearing options and lock out.
    Enduro/Freeride/AM typically have 1 or 2 ring set ups and depends heavily upon rider input/fitness level and how you build up your ride.
    And yes you can change cassettes for different gear ratios, but changing sprockets is cheaper.
    Not sure why you would want to lock out the suspension on the bird it climbs anything you have the power & skill to climb
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  17. #17
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    I have a PhD in knee rehabilitation and I have been pondering your problem for a few days. I can't see that pedal feedback would have a significant or measurable impact on you knees. ddprocter has nicely outlined some other potential areas that may be worth investigating - particularly strength training in increase joint stability around the knee.
    Trust me it does. When I went from my old blur to a HL bike,
    the difference wwas spectacu;lar

  18. #18
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    Quote Originally Posted by Mt.Biker E View Post
    Not sure why you would want to lock out the suspension on the bird it climbs anything you have the power & skill to climb
    Because apparently the pedal feedback is causing knee injury to the OP, and locking out the rear sus would eliminate it. If this is something the OP doesn't want to do, then other solutions are necessary. (Such as increasing chainring size to reduce pedal feedback and change the cassette to keep the overall ratio closer to what he had earlier.)

  19. #19
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    Quote Originally Posted by Saul Lumikko View Post
    Because apparently the pedal feedback is causing knee injury to the OP, and locking out the rear sus would eliminate it. If this is something the OP doesn't want to do, then other solutions are necessary. (Such as increasing chainring size to reduce pedal feedback and change the cassette to keep the overall ratio closer to what he had earlier.)
    Its not causing his knee injury, he has bad knees due to a crash. The best thing for knee injuries is strength training and loss of body mass.
    Life in every breath

  20. #20
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    If you say it's causing knee pain, I'll accept that.

    It's a shame you probably live thousands of kilometers away, would be interesting to somehow attach a dynamometer to the pedal / shoe interface (a few different ways this could be done). Even some EMG to measure muscle activity and co-contraction. It would be interesting to see what sort of forces may be spiking during the pedal feedback.

  21. #21
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    Re: Pedal feedback: Coming full circle

    On my last ride, i tried to recreate this very carefully, rolling over mid sized bumps while pedaling under power, and I'm starting to come around on this. Exactly as Le_Buzz said in his original post, on a dw link bike, bumps force the rear wheel further rearward, adding extra tension to the chain mid stroke. It doesn't bother my knee too much, but i could see how it could. It feels like the knee is especially vulnerable to this at around the 2 oclock-3 oclock position, when the knee is both at a high angle of flexion, at at the same time somewhat forward, close to the over-forward position where the knee is almost vertically over the ball of the foot, or even over the front of the toe if your saddle is too far forward. This position (often called out as the dreaded no-no way to do lunges in the gym), combined with some some DW-link induced tension from a bump, could cause knee pain for sure.

    Uphill=Sad, as a PhD, does this seem plausible?

    Anyways, if true, Saul, i gotta respectfully disagree here:

    Quote Originally Posted by Saul Lumikko View Post
    Because apparently the pedal feedback is causing knee injury to the OP, and locking out the rear sus would eliminate it. If this is something the OP doesn't want to do, then other solutions are necessary. (Such as increasing chainring size to reduce pedal feedback and change the cassette to keep the overall ratio closer to what he had earlier.)

    Changing both the chainring and the cogs, yielding the same ratio, will have no effect on the op's problem:

    If the rider has the same leverage on the trail, then, at the same time, the bumps on the trail have the same leverage on the rider, and the pedal feedback will be exactly the same. Its just simple physics.

    Now, keeping this line of reasoning, spinning a higher gear, or, changing to bigger chairing only, will decrease the leverage that the rider has on the trail, and increase the leverage that the bumps have on the rider, exacerbating the pedal feedback. So, I think op might want to try spinning higher cadence, lower gears for a while and see if that helps.

    And, Le Buzz, most importantly, since your injury is Chondromalacia, I REALLY, REALLY recommend you try McConnel Taping a.k.a. Patelarfemoral taping. Its just a technique to tape the kneecap either inboard or outboard, depending on your injury, where it should be if you had perfect mechanics. Have your physical therapist show you how to do it, and try it in a few physical therapy sessions to get it right (you can tape it too far if you don't get it dialed). Then, you can get a McConnel tape combo pack off Ebay and tape yourself. There are 2 tapes: an cover-role stretch underlayment and a leukotape, which is an ultra-sticky, stretchy wide athletic tape. You'll need a combo pack like this one:

    Leukotape P Cover Roll Stretch Tape Combo Pack | eBay

    A friend of mine is the professional trainer for a D2 college program and highly recommends it. You can do it temporarily until you get better, or permanently - it only takes a couple mins before each ride and makes a big difference. But as always 'your results may vary'.
    Last edited by Procter; 02-12-2013 at 12:22 AM.

  22. #22
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    Quote Originally Posted by ddprocter View Post
    On my last ride, i tried to recreate this very carefully, rolling over mid sized bumps while pedaling under power, and I'm starting to come around on this. Exactly as Le_Buzz said in his original post, on a dw link bike, bumps force the rear wheel further rearward, adding extra tension to the chain mid stroke. It doesn't bother my knee too much, but i could see how it could. It feels like the knee is especially vulnerable to this at around the 2 oclock-3 oclock position, when the knee is both at a high angle of flexion, at at the same time somewhat forward, close to the over-forward position where the knee is almost vertically over the ball of the foot, or even over the front of the toe if your saddle is too far forward. This position (often called out as the dreaded no-no way to do lunges in the gym), combined with some some DW-link induced tension from a bump, could cause knee pain for sure.
    Sounds plausible to me, a combination of these factors is the likely cause.

    While I don't think there is any specific flexion angle the knee should not be at, (in a gym setting) the no more than 90 degree thing more than anything probably helps overall posture and limiting maximal ROM in a knee with patella tracking issues is a good thing.

    The problem with le_buzz's knee is that the if there is any patella tracking issues (almost always is) the knee is at it's most symptomatic ROM - due to decreasing moment arms of the quads and quite a large movement of the patella. At this point, some pedal feedback - even though I don't think it would be applying much in the way of force into the knee, it's occurring in the worst possible time.

    The patellofemoral taping is a solid recommendation, le_buzz, if not sure get your therapist to show you. Not sure if your using flats or clipless, if clipless have you tried pusing the cleats as far gack as possible - with will limit (slightly) maximum flexion, might help just a little.

    I played around yesterday, a few more clicks of LSC helped my pedal feedback - but a small amount of traction / plushness was lost.

    Does your knee get worse on a longer ride - towards the end? is fatigue related to your symptoms? would shortening the length/time on the ride help?

  23. #23
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    Quote Originally Posted by ddprocter View Post
    On my last ride, i tried to recreate this very carefully, rolling over mid sized bumps while pedaling under power, and I'm starting to come around on this. Exactly as Le_Buzz said in his original post, on a dw link bike, bumps force the rear wheel further rearward, adding extra tension to the chain mid stroke. It doesn't bother my knee too much, but i could see how it could.

    Anyways, if true, Saul, i gotta respectfully disagree here:

    Quote Originally Posted by Saul Lumikko View Post
    Because apparently the pedal feedback is causing knee injury to the OP, and locking out the rear sus would eliminate it. If this is something the OP doesn't want to do, then other solutions are necessary. (Such as increasing chainring size to reduce pedal feedback and change the cassette to keep the overall ratio closer to what he had earlier.)
    Changing both the chainring and the cogs, yielding the same ratio, will have no effect on the op's problem:

    If the rider has the same leverage on the trail, then, at the same time, the bumps on the trail have the same leverage on the rider, and the pedal feedback will be exactly the same. Its just simple physics.
    I might be wrong about pedal feedback causing knee pain, but I'm quite sure about chainring and sprocket size having an effect on pedal feedback and pedal bob - even when the overall gear ratio is the same.

    When comparing a big-big combo (44/22 for example) to a small-small (22/11 for example) the chain is moving twice as fast but pulled by the chainring at half the tension. However, the rearward movement of the rear tire during compression is fixed - doesn't matter what gear you're in.

    Let's say the rear wheel moves 2 cm further from the BB during compression. Select a granny chainring and pull the chain 2 cm. Note how much the cranks turn. Then select a larger chainring and pull the chain 2 cm. You will see that the cranks rotated much less this time.

    For this reason the small-small combo will reduce pedal bob but increase pedal feedback, while the big-big combo increases pedal bob, but reduces pedal feedback. Basically it's just the size of the chainring that matters. If someone has too much pedal feedback but don't want to sacrifice their low gears, they can switch to a larger chainring and increase sprocket size to compensate.

  24. #24
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    Thamnks for all the helpful replies Saul and ddproctor.
    Some rear susp.designs are more prone than others
    to pedal feedback. The designers try to reduce the amount
    of antisquat toward the end of travel to alleviate this as much
    as they can, but some always seems to sneak through.
    My Santa Cruz blur had the worst pedal feedback of all the
    bikes Ive ridden,; I would have knee pain after rides and
    it drove me crazy until I sold it. My next bike was a
    Chumba XCL. It wasw a relief to be able to pedal up rocky
    climbs without knee pain.

    Some knee pain has come back on the Firebird. Right now
    Im trying to monkey with the rebound and such. I think
    there's things I can do with the setup to mitigate it more.

    The best thing I think, would be to go the route that Saul mentioned:
    Go to a 1X9 setupl, with a single 30 tooth abd a 38 or 40 large
    cog in back. I also want to go coil for some extra plushness.
    Do you think that would have a beneficial effect ?

  25. #25
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    Quote Originally Posted by Saul Lumikko View Post
    I'm quite sure about chainring and sprocket size having an effect on pedal feedback and pedal bob - even when the overall gear ratio is the same.

    When comparing a big-big combo (44/22 for example) to a small-small (22/11 for example) the chain is moving twice as fast but pulled by the chainring at half the tension. However, the rearward movement of the rear tire during compression is fixed - doesn't matter what gear you're in.
    Ahhhhhh, you're riiiiight. To put this a different way, pedal bob and pedal feedback aren't related to the overall gear ratio pedal-to-wheel, only the gear ratio 'that the front of the bike has against the back of the bike' in a way. This is because they both have nothing to do with net torque at the wheel being transferred back to the pedal, but rather torque at the pedal relative to suspension compression (in the bob case) and the pedal relative to momentary chain tension caused by rearward travel during a bump (in the feedback case).

    But, I think the conclusion is the opposite of this:

    For this reason the small-small combo will reduce pedal bob but increase pedal feedback, while the big-big combo increases pedal bob, but reduces pedal feedback.
    In pedal bob, rider's input at the pedal adds tension at the chain, which pulls on the rear linkage in such a way that it compresses the suspension. More leverage at the pedal (smaller chainring) gives the rider more leverage against the resisting force (the shock), which yields more bob.

    In pedal feedback, a bump compresses the suspension, moving the wheel rearward on DW link bikes, tensioning the chain more, which adds momentary counter-force @ the pedal, possibly causing knee pain for a knee already in mid-flexion and moving in a forward circle at a good velocity. In this case, more leverage at the pedal (smaller chain ring) reduces the leverage that the chain has on the pedal, reducing the momentary counter force applied at the rider's knee.

    So I think smaller chainrings to fight feedback, bigger chainrings to fight pedal bob.

    Do you agree or am I wrong?

    Talk about coming full circle, I just completely changed my thinking on this from my first post to my last :P

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