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How to tune Single Pivot Falling rate bikes?

Discussion in 'Downhill & Freeride' started by nickfr2000, Feb 7, 2008.

  1. nickfr2000

    nickfr2000 Chimp

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    I have a MC Sin with a Progressive 5th element. I know it is a falling rate design. For owners with single pivot bikes with 5th element or similar platform shocks with high / low speed compression adjusters; what are your rear suspension settings?

    Thanks in advance.
     
    #1 -   Feb 7, 2008

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  2. NEstinkyrider

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    how do you know it's a falling rate design? i'm just curious, it seems like some people can just look at a frame and state wether it's a falling, linear or rising rate design.

    also, what is the i2i on the shock? i'm interested in getting a sin.. good deals online right now..

    just concerned about the 14.8" bb height.. i like my bikes a bit lower..
     
  3. nickfr2000

    nickfr2000 Chimp

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    It felt like a falling rate design as it is stiff at first / while pedalling / when launching the bike from a lip; but then again blows through the travel after the initial compression. Since no one has responded to this crazy question, I was able to tune it to my liking with my 7.875 x 2.25 Progressive 5th element 5way. Basically with 30% sag achieved with a 550lbs spring for a 220 lb rider, I set the rebound 30% from full slow, 20% high speed compression from fully open, low 65% low speed compression from fully open, 100psi CVT pressure, & 50% CVT volume.

    I got my brand newMC Sin w/5th element shock directly from MC HQ for $375 as a no warranty frame. Eric told me to try to ride it conservatively to prolong the service life but for the price I couldn't care much. I got the relaxed shock cleat which lowered the BB from 14.83 to 14.25 as well as slackening the HA by around 1 degree achieving a guestimated 67 deg. Unfortunately it also decreased the travel from 7.5 to 6.7 as well as changing the leverage ratio from 3.3:1 to 3:1.

    BTW my bike was set up with a '06 66 RC2x and high volume 2.5 tires.
    Here is a pic.
     
  4. engineerjoe

    engineerjoe Chimp

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    I believe a "falling rate" design corresponds to the lever ratio of the wheel movement to the compression of the shock.
    I can tell you that that bike is not a falling rate design based on the positioning of the front pivot of the swingarm relative to the shock pivot at full copression.
    Your shock must have been set up improperly or set up for better pedaling - turn your low speed comp down
     
  5. nickfr2000

    nickfr2000 Chimp

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    I'll keep it in mind but my current setting suites my style. The bike has a very short cockpit that is why most of the time I am riding behind the seat. In these situations the LSC is keeping the bike from blowing through the travel.
     
  6. davep

    davep Turbo Monkey

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    For a simple single pivot (no shock activation linkage) the angle defined by the line along the shock and the line defined by the pivot and the seingarm shock mount can give good insite if the frame is 'falling' or 'rising' rate.
    In general if the angle goes toward 90* as the suspension compresses (as this frame does) the the design is a rising rate. If however, the angle goes away from 90*, the design will be a falling rate.
    rising rate/progressive

    falling rate/regressive

    keep in mind, that this is only a first order approx....but if the change in angle is obvious..like the pics above, you should be able to determine what is going on.
     
  7. buildyourown

    buildyourown Turbo Monkey

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    The symptoms you describe sound like you have to much air pressure. Remember, the "platform" is set by the pressure. More pressure, and the bike will ride firmer, but only at the beginning of it's stroke. After it, blows through the platform, it will cycle like a normal shock. This blow through could feel like a falling rate.
    When I first got my 5th, I had a horrible time tuning it. I eventually realized that I was running a too light spring. Don't always trust the spring calculators.
    Personally, for pure DH, 100psi is too much. If you can't get it to run without bottoming out with 50psi in it, and no excessive compression, your spring rate is too soft.
     
  8. dhkid

    dhkid Turbo Monkey

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    BYO, i dont think thats a good way of explaining how the 5th works. i find that gives more and more damping deeper into the travel. maybe you feel it 'blows though its travel' because of its initial stiction, which on stock 5ths are pretty high. on drops to hard landing and everywhere else my 5th uses much less travel then my dhx and feel more controlled. makes the dhx feel like its blowing though the travel, which it is.

    nickfr - i would start by lowering your pressures like buildyourown said, just to get a starting point to work with. but looking from your weight you dont want to lower it that much. maybe start around 70 or 80.

    the main adjustment you should be looking at is the chamber size, that will control the progression. and it would make a much bigger difference then the beginning and ending stroke compression adjusters. after you are happy with what you have for jumping, make sure you test it on a rock garden or a root section and make sure you are not getting too much damping. then back off slightly.
     
  9. joelsman

    joelsman Turbo Monkey

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    you should try a heavier spring and less low speed compression. with a 3:1 ratio and you at 220, 3x220= 660. you should try a 650lb spring.
     
  10. bElliott

    bElliott Chimp

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    i,ve got a gemini(whichibelieve is actual falling rate), and have the same problem. 7.75x2.25, 3:1 ratio, and 550 spring

    i weigh 170-180 w/gear.

    i can bottom it out sooo easily "parking lot". but i cant tell if i have too much compression on the trail or its just bottoming off of everything.

    any tips or anything is appreciated.
     
  11. MorewoodKid

    MorewoodKid Monkey

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    but remember:
    falling spring rate = a rising compression rate
    rising spring rate = a falling compression rate
     
  12. P.T.W

    P.T.W Monkey

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    explain???????????????:crazy:
     
  13. NEstinkyrider

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    davep: thanks for that response.. that was quality :rockout:
     
  14. nickfr2000

    nickfr2000 Chimp

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    Thanks for the insight Davep! If my suspension design is indeed progressive / rising rate; does this mean that I could use less progressive shocks like the Roco WC, Romic, or Vanilla RC?

    I'll try to follow your advices guys and back off my compression a little bit as well as reduce my CVT pressure.