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Why is unsprung weight bad?

Discussion in 'The Garage' started by Paxx, Jan 15, 2004.

  1. Paxx

    Paxx 1/2 ton status

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    I can understand how a heavier tire/wheel combo can increase breakage, but say if your axle itself weighed an extra 50lbs wouldn't it just help keep your tires on the ground and your center of gravity lower?
     
  2. tomseviltwin

    tomseviltwin 1/2 ton status

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    Many the "professional" rockcrawlers are running water in their tires to lower the center of gravity, so it must not be all bad /forums/images/graemlins/thumb.gif
     
  3. Paxx

    Paxx 1/2 ton status

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    I just keep on hearing about all these people saying "ya thats a nice part but your gonna increase your unsprung weight" etc. so I was wondering why its supposed to be such a bad thing
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    At very low speeds, I'm not sure I can think of a reason to worry about unsprung weight.

    The problem is at anything resembling street/highway speeds. Any weight that exists under the spring has to follow the profile of the road, and the more mass it has, the less likely it is to follow the surface variations. More likely, it will collide with the first big bump, then leave the ground entirely for a brief period of time. The damper (shocks) can only do so much to slow that mass down. Even the best shocks in the world won't be able to accurately control a heavily sprung mass, and the vehicle will sort of "skip" from bump to bump down the road.

    This is most disconcerting around a bumpy corner, because each time you are in the air, the truck will be trying to go off the outside edge of the turn!



    Anyway, that's my overly simplified example to help explain it. If we were designing racecars, this would be a LOT more important. In the context of our low-speed sport, it just doesn't seem to have the same importance.
     
  5. Paxx

    Paxx 1/2 ton status

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    hmm I see well that I can understand /forums/images/graemlins/thumb.gif
     
  6. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Anyway, that's my overly simplified example to help explain it. If we were designing racecars, this would be a LOT more important. In the context of our low-speed sport, it just doesn't seem to have the same importance.

    [/ QUOTE ]
    I agree with Greg... it's important if your building a fast handling car but not as much with lifted trucks that are already heavy.
     
  7. BowtieRed

    BowtieRed 1/2 ton status Author

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    in mud it's obviously a problem- when stuck and jamming gears, the force applied to the axle is greater with the increased weight. basically the force generated can only be equal to the resistance, more resistance more force more breakage. water wont hurt this as it doesn't follow the path of the tire so it does not have to reverse directions with the tire. it's basically like dropping the clutch while on an axle lift as opposed to while on the ground chained to a wall. more resistance.
     
  8. jeffro

    jeffro 1/2 ton status

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    It also matters what the truck weighs. On a lighter rig more unsprung weight is worse than a heavier rig. The sprung weight is pushing the unsprung weight down. If the difference is too great the axles will throw the truck around like a bobble head doll. This is Isaak Newtons fault for causing objects in motion to tend to stay in motion.
     
  9. Paxx

    Paxx 1/2 ton status

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    thnx for all the replies guys /forums/images/graemlins/thumb.gif
     
  10. tomseviltwin

    tomseviltwin 1/2 ton status

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    Yes, good info.
     

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