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[Video] MTB rear suspension fundamentals

AndreXTRAndreXTR Posts: 64
edited March 2016 in MTB workshop & tech
Hello!

Just wanna to share my video about the basic theory behind rear suspension / linkage.

Topics covered in the video: Leverage ratios (LR), LR variation & progressivity, suspension forces and shock (air & coil) forces.

v806ki.jpg
https://www.youtube.com/watch?v=A1dUV6pYztg

Sorry for my portuguese accent :D
Hope you enjoy it.

Posts

  • Good effort, expect some stupid comments from brianbee though!

    eheheh its ok :lol:

    Thank you!
  • RockmonkeySCRockmonkeySC Posts: 15,247
    Nothing about the damping in air springs?
  • Nothing about the damping in air springs?

    Maybe in the next video. I want to keep it simple in this first video... which is already quite long :)
  • RockmonkeySCRockmonkeySC Posts: 15,247
    Joking dude. There's a moron in another thread who insists air springs and dampers are the same thing.
  • Dirtydog11Dirtydog11 Posts: 1,621
    Sorry for my portuguese accent :D
    Hope you enjoy it.

    Yeah enjoyed that, well explained.

    Anti Squat next.
  • Second video of "MTB rear suspension" series :)

    https://www.youtube.com/watch?v=ViSyAOKYnqw
  • Hi guys! My third video!

    The reason why you shouldn't use Preload in your coil shock or fork.

    2a0l5ci.jpg
    https://www.youtube.com/watch?v=ViSyAOKYnqw
  • 4th video of this serie!!

    Today I will talk about suspension systems. Which is the best system? VPP, FSR, Singlepivot? Check this out :)

    https://www.youtube.com/watch?v=78DD82fx4M8

    Bye
  • AndreXTRAndreXTR Posts: 64
    Hi!

    8th Episode of the serie :)

    In this video I will show you what is the breakaway force, how to measure it, and how it affects the suspension performance.

    0.jpg
    https://www.youtube.com/watch?v=I68FNkffbhI

    Enjoy!
  • Angus YoungAngus Young Posts: 3,063
    Great stuff. Keep 'em coming.
    All the gear, no idea and loving the smell of jealousy in the morning.
    Kona Process 134 viewtopic.php?f=10017&t=12994607
  • supersonicsupersonic Posts: 82,708 Lives Here
    Some good stuff, though I have not watched them all yet.

    Regarding the preload, if when ridden the shock is in a loaded and sagged state, when a bump is encountered it makes no difference to how far the shock moves for that hit (assuming linear suspension characteristics), all that has changed is ride height - your weight has already provided the initial force, and overcome the preload, hence why has sagged(if not wound on too far so as to not sag at all). But of course in the real world the wheel leaves the ground often, this is where it can be felt, and when it is very lightly loaded and not sagged. Which is what the drop test is demonstrating - the shock is initially at full extension and unsagged.

    Ep 4: I thought was going to be about anti squat and braking characteristics, is this covered elsewhere?
  • You explain the forces required for the fork/shock to break stiction well.

    But from what I can see from your videos is that you are carrying out the tests without a real load. This changes the whole suspension characteristics.

    The forks and shocks were designed with a load in mind, before they start to operate.

    From your videos you are suggesting the shocks/forks operate in a micro gravity environment.

    I don't agree with your findings.
  • AndreXTRAndreXTR Posts: 64
    The forks and shocks were designed with a load in mind, before they start to operate.

    From your videos you are suggesting the shocks/forks operate in a micro gravity environment.

    I don't agree with your findings.

    Shocks are not designed with a load in mind. The breakaway force is a undesired side effect of the IFP pressure. Indeed brands are trying to produce shocks with zero breakaway force. Ohlins TTX and DVO Jade use a bladder instead of IFP to achieve this. EXT ARMA uses a very low IFP pressure also to reduce breakaway force. And RS Vivid uses a negative coil spring inside the damper also to reduce the IFP-derived breakaway to zero.

    Here's some quoting:

    EXT: "The damper run with very low Reservoir pressure 30 Psi this
    dramatically improve first movement sensitivity, comfort hence
    traction and safety."

    RS VIVID: "Counter-measure: Engineered For The Elite, the new Vivid conquers several once-thought-impossible engineering feats. Technologies like Counter Measure, which reduces the breakaway force of the shock to virtually zero pounds, transforming small bumps in to traction-generating performance."

    DVO JADE: "BLADDER: AMAZING SMALL BUMP COMPLIANCY, NO STICTION OFF THE TOP." "Instead of using an Internal Floating Piston (IFP), DVO chose to use a bladder in the coil-sprung Jade rear shock, a design intended to reduce any potential initial stiction, which helps improve small bump sensitivity."



    Indeed, zero breakaway is what manufacturers aim to have. We can discuss this issue better if you want, but there is no advantage to have a breakaway force higher than zero. Just to add more info, the breakaway force measured is the net result of the preload (static force) + stiction. Where static force is produced by the preload on the air/coil spring and by IFP (IFP preload force = IFP pressure in PSI x shaft area in square inches). The stiction cames from the linkage, shock bushings and shaft/sealings. The sum of all this things is what you get on the weight scale test.

    So yes, your bike should have a tiny amount of SAG by itself (static SAG), as motos and cars also have. The reason that in most cases bikes don't have SAG is because they are very too light for the breakaway forces present in the suspension.

    And yes, when you are running on a bumpy trail you have that "micro-gravity", indeed, if you look to slow motion videos you will see that the wheel is not always touching the ground in a rocky terrain. Indeed the weigth load on the wheels changes drastically and very rapidly between 0 and ~80 kg on a bumpy trail.

    Bye :)
  • AndreXTRAndreXTR Posts: 64
    Hello guys! Just to share another episode!

    Hope you like it! Bye.

    Episode 9
    0.jpg
    https://www.youtube.com/watch?v=IyH8hNLr1m0
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