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Thread: loss of travel

  1. #1
    Senior Member bigjsp's Avatar
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    loss of travel

    Made this drawing for a statement I had made about loss of travel for bag behind the axle versus bag over axle.


    In the configuration I show a 24 inch link with 8" bag mounted 4" behind vs on top.


    The bag behind has 1.19" less axle movement
    Last edited by bigjsp; 02-16-2007 at 11:08 AM.

  2. #2
    Senior Member bigjsp's Avatar
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    can't add pics

    and can 't delete a first post

    so +1

  3. #3
    Registered User AIR SIC's Avatar
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    Nice diagram Big, I've pictured it in my head but never drawn it out.

    Also, by your diagram most bags would have to be even farther behind the axle than that. Most minitruck axles are 2.75" dia/1.375" radius,a Firestone 255c has a 3.2" max radius, a Slam RE-7 has a 3.5" max radius, and a Firestone 224c has a 4" max radius. That totals out to 4.575", 4.875", and 5.375" respectively, all losing even more effective lift by having to move them back farther than 4" from the center of the axle. :bigthumb:

  4. #4
    Senior Member bigjsp's Avatar
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    understood and agreed.

    the effects of pressure are another item that this small difference make as the same reduction in lift is accompanied by a proportional reduction in pressure

  5. #5
    Registered User AIR SIC's Avatar
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    Originally posted by bigjsp
    understood and agreed.

    the effects of pressure are another item that this small difference make as the same reduction in lift is accompanied by a proportional reduction in pressure
    true true

  6. #6
    Ruling Member zombie's Avatar
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    it makes complete sense. so by doing a mount in front of the axle you would gain a bit of lift correct?

  7. #7
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    yeah but the way i see it you will need more psi.

  8. #8
    Senior Member bigjsp's Avatar
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    Originally posted by lowestyet1
    yeah but the way i see it you will need more psi.
    correct

    with forward links, bags in front, configured to get 10% more lift than over axle you would need 10% more pressure to achieve the same axle travel.

  9. #9
    School Of Air Ride
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    You are partially correct, and partially incorrect.

    I was/am following your debate S10Forum with PhatBoy and you guys are both correct, but it is situation dependent. I wish I could post over there, but being banned makes that hard to do.

    You would be correct if the axle rotated the same amount as the 4 link/3 link/ 2 link bars. With a 2 link, this is 100% true, the further back you mount the bag, the less lift you have. However, with a 4 link or 3 link, in which there is little to no pinion angle change (actually, if the pinion were to dip downwards on lift, you would get more lift with a behind the axle setup, but I digress), the vertical height between the axle mount and frame remains the same over or behind the axle, making PhatBoy correct.

  10. #10
    Senior Member bigjsp's Avatar
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    any links showing this?


    I'll model it up at work next week as I don't have CAD at home.

    any preferences for link lngths and initial angles?



    I guess I should make allowances for people running suspensions that would not be compatible with V8 power.

    like instant centers behind the rear axle, etc. LOL

  11. #11
    www.guiltybydesign.net guiltybydesign's Avatar
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    Ive also done some thinking on this. Having the bag in front of the axle usually means its on the link bars, so of course your going to get more lift. If you were to run your 4 link bars past your axle and then mount the bags on them then yes you would def loose lift. But if you were to take a behind and under axle bracket and weld it on the front of the rearend would you really get anymore lift? Realisticly its still lifting from the axle.

  12. #12
    Senior Member bigjsp's Avatar
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    I have every bit of confidence in calculations for the 2 link.


    I will examine what happens to lift when we move the mounting point as a function of link / pinion induced angle changes for the 3 and 4 links


    I'm not expection alot of change due to this but time will tell.

  13. #13
    School Of Air Ride
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    Originally posted by bigjsp
    I have every bit of confidence in calculations for the 2 link.


    I will examine what happens to lift when we move the mounting point as a function of link / pinion induced angle changes for the 3 and 4 links


    I'm not expection alot of change due to this but time will tell.
    I think you'll be surprised. I know you're trying to think of things in the arc of a circle, but when the axle's angle doesn't change with the angle of the bars (as in the case of a proper 4 link or 3 link), that line of thinking doesn't apply.

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