Lift Shackles & Leaf Spring Flex/spring Rate

KC! Nov 26, 2019

  1. KC!

    KC! Bought an X

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    How do lift shackles make the leaf springs response softer? I’ve heard about the angle of the shackle mount in regards to the leaf spring eye but nothing definitive on specifically I guess the physics behind the softening of the springs. Thanks! If there’s another thread that already touches on this in depth, I can post it there.
     
  2. IM1RU

    IM1RU First Fill-Up (of many) Supporting Member

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    Location:
    SLC, UT
    I'm not so sure they make the response softer, but they do allow for more flex or lengthening of the spring when compressed which can eventually flatten out the springs or rather speed up their flattening.... Particularly the stock springs, which are fairly weak to start with. Thus the need for bump stops. If the bump stops don't contact the axle soon enough the spring can actually invert, and really flatten out fast, or break.
     
    scoyoc likes this.
  3. KC!

    KC! Bought an X

    Messages:
    146
    That makes sense, I found a diagram on online about the angle of the mount and the length of the shackle. It was stating that the leaf spring gets elongated with longer shackles which I agree, doesn’t make response softer now that I think about it haha, but elongates the spring by lengthening the at rest leaf spring arch. Which I think gives you more travel before you elongate the spring enough to compress back to the resting arch? This is just my theory but it’s really interesting too me! I’ll see if I can find that diagram.
     
    scoyoc likes this.
  4. KC!

    KC! Bought an X

    Messages:
    146
    I did some more research and thinking, and my final theory is that the shackle angle is used to manipulate how the weight that the leaf springs support is distributed in relation to the eye. If you have an angle where the shackle is closer to that "B" line, you have more of the weight pushing down and twisting the spring clock-wise, This would make it "softer" but would really just make the spring compress further. If the shackle is closer in relation to "A", the weight will still be down and wanting to flatten the spring, but the torque on the spring eye will be counter-clockwise which will promote the spring to arch instead to flatten or compress along with the down force.

    In terms, of how the length of the shackle affects the up travel, since all of the weight is being pushed up higher due to the length of the shackle. Your potential energy will increase with that height increase in relation to the leaf spring, which means the downward velocity all of the weight supported by the leaf spring (rear of the car) will increase. The energy is conserved therefore, the amount of displacement in the leaf spring will increase because energy from the vehicle is transferred to the spring in terms of elastic potential energy. More EPE equals more displacement in the spring, which is the additonal "flex" given. Momentum is also in play here and the vehicle will have more momentum because it has more kinetic energy, which is transferred to the spring. This work together though and it dives deeper than I desire. Feel free to chime in or point out any mistakes in my thinking!

    Also, I hope everyone has a Happy Thanksgiving!


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    Last edited: Nov 28, 2019
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  5. IM1RU

    IM1RU First Fill-Up (of many) Supporting Member

    Messages:
    354
    Location:
    SLC, UT
    Happy Thanks giving...

    You think too much.
     
  6. KC!

    KC! Bought an X

    Messages:
    146
    I know... it’s all these engineering courses I’m having to take:(
     

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