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How does 3 inch lift kit work?

Discussion in 'Suspension' started by drifter, Apr 22, 2012.

  1. Apr 22, 2012 at 7:01 PM
    #1
    drifter

    drifter [OP] moderately modded

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    Hello,
    How does the 3 inch lift kits for our trucks work exactly? A 3 inch spacer lift seems to consist of an approximately 1.5 inch thick spacer. I am assuming that this is due to the position of the strut on the LCA. If this is the case, and I believe that it is, then if the bottom end of the strut was closer to the wheel then the spacer would need to be thicker. And, if the bottom end of the strut was further away from the wheel then the spacer would need to be thinner. It is all relative to the angle of the strut on the LCA, correct? If you guys could verify this for me I'd appreciate it.

    Does anyone have any good sources that explain how this works? I am trying to write a paper on this for school; a legitimate source to back up my explanations would be awesome.

    Thanks,
    Sam S
     
  2. Apr 22, 2012 at 7:07 PM
    #2
    bjmoose

    bjmoose Bullwinkle J. Moose

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    Steve
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    Google double wishbone suspension geometry.
     
  3. Apr 22, 2012 at 7:07 PM
    #3
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Staff Member

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    FlimFlubberJAM
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    You got it right. Being as the coilover assembly is half way between the control arm mounts on the frame, and the spindle, it lifts at a 2 to 1 ratio. every 1" of lift at the coilover, equals to 2" lift at the wheel.
     
  4. Apr 22, 2012 at 7:08 PM
    #4
    Rich91710

    Rich91710 Well-Known Member

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    You are correct.

    3" at the spindle = 1.5" roughly (not exactly) halfway out on the LCA.
     
  5. Apr 22, 2012 at 7:12 PM
    #5
    drifter

    drifter [OP] moderately modded

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    This is great. Thanks guys!
     
  6. Apr 22, 2012 at 7:41 PM
    #6
    Large

    Large Red

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    I think this should be stickied. I've never seen this info, and it's pretty useful. My $0.02
     
  7. Apr 22, 2012 at 8:36 PM
    #7
    Rich91710

    Rich91710 Well-Known Member

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    Don't they teach basic geometry in school anymore?

    Seriously... this is 5th grade level stuff.
    You can figure it out by watching two friends on a see-saw.
     
  8. Apr 26, 2012 at 5:00 PM
    #8
    drifter

    drifter [OP] moderately modded

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    Ok, stupid question: is there a technical/mathematical term for this? I'm having trouble putting this concept into words...
     
  9. Apr 26, 2012 at 5:03 PM
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    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Staff Member

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    Yes. Its called "double wishbone suspension geometry. " Depending on where the shock is mounted between the Control arm mounts on the frame, and spindle, determins what leverage ratio the shock/spring will have.
     
  10. Apr 26, 2012 at 5:07 PM
    #10
    Pugga

    Pugga Pasti-Dip Free 1983 - 2015... It was a good run

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    It's geometry, simple lever. Ever wheel a wheelbarrel? The tire is the fixed point, just like where the LCA bolts to the frame. Then, you lift from the end of the handles, say you lift up 2', the feet only lift up 1' off the ground. Same idea with the front suspension. Like BJ Moose said, good Double Wishbone Suspension.
     
  11. Apr 26, 2012 at 5:25 PM
    #11
    Rich91710

    Rich91710 Well-Known Member

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    Yup...

    In it's most basic form, it's a simple lever.

    In reality, the geometry results in a number of variables. If the strut is not perpendicular to the arm, then 1.5" won't = 3" at the end.. it'll be less.
    Of course, the strut is only perpendicular to the arm at one point in the travel... and some suspensions are designed with the top of the struts canted inward so they are only parallel with the arm when fully compressed.


    So yes, there is math that can give exact results. Suspension tuners use this math... but it is pretty complex... which is why everyone just says "1.5 = 3"...

    It falls under "close enough" engineering for 90% of those looking for the answer.
    For those where "close enough" isn't close enough, they already know the theory and have access to the math to get the exact results.
     
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