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  1. #11
    Super Member N80's Avatar
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    Aug 2005
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    5,244
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    SC
    Tractor
    Kubota L4400 4wd w/LA 703 FEL

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    At least my general experience mirrors the math, whether it is ugly or not. My rear tires were factory filled but with a full bucket things felt just a little squirrely when I hit a bump or travelled at speed. Then I got a box blade. I think it weighs 600+ pounds and it made a _huge_ difference as a counterweight when using the loader. Box blades are pretty unobtrusive as far as implements go, so it stays on when I'm using the loader.
    George
    South Carolina

    The size of government is inversely proprotional to the degree of freedom it affords.

    "What is truth?" Pontius Pilate

  2. #12
    Silver Member
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    May 2006
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    236
    Location
    Purcellville, Va
    Tractor
    B7200D, B8200D

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    Quote Originally Posted by JoeL4330
    Does the loader CG stay constant (fore-aft) as it moves?

    And, w.r.t. the "sprung/unsprung weight" comment ...whose tractor has springs?
    Mine sure doesn't but that's still the best term to describe the physics. Your tires sit on the ground. The tractor hangs from the axle between them. Adding weight to the tires doesn't add direct stress to the tractor; i.e. it doesn't place additional weight on the axles. Adding weight to your 3pt hitch adds weight and stress on the axles which is then transferred through the tires to the ground.

  3. #13
    Elite Member schmism's Avatar
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    Jul 2006
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    4,945
    Location
    Peoria IL
    Tractor
    New holland TC(33)

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    AH im always a sucker for a good FBD

    but way to much sketchy stuff in there... should just be distances, weights and arrows.


    and to be picky....

    if you note the CG for the loader above the CG for the tractor...
    the combined CG is between the 2 (ie higher off the ground)

    by adding liquid ballast to the bottom half of the tires you can lower the CG back down. Same goes for the height of your counter weight off the rear.
    Steve - TC33D 4x4 FEL, dual rear remotes with toys

  4. #14
    Super Member California's Avatar
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    Jan 2004
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    5,744
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    Sonoma County
    Tractor
    Yanmar YM240, YM186D, and another YM186D

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    ... if the tractor tips forward slightly the CG moves AHEAD of the front wheels and you do a nose dive. ... going over the transom caused the pallet fork truck to tip right onto its nose.
    And since a tractor doesn't have front springs there is nothing to control it to tip straight forward. An off-center CG might put the tractor on its side.

  5. #15
    Elite Member dfkrug's Avatar
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    Feb 2004
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    4,662
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    NorCal
    Tractor
    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    Quote Originally Posted by California
    An off-center CG might put the tractor on its side.
    This is also a big issue with fluid-filled tires. The CG of the tires
    moves as the tractor tips sideways, increasing the rollover potential.

    WHODAT90 beat me to it, but it is also true that adding fluid or
    wheel weights adds NO static rear axle load. Even if the CG of
    the whole tractor is affected.

  6. #16
    Silver Member
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    May 2006
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    236
    Location
    Purcellville, Va
    Tractor
    B7200D, B8200D

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    Another thing pointed out (obliquely) in the 4x4 thread is that filling your tires makes the rear of the tractor heavier. Adding weight to the 3pt makes the rear of your tractor heavier and the front lighter. Big difference when you don't have a load in the bucket.

  7. #17
    Veteran Member daTeacha's Avatar
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    Oct 2005
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    2,352
    Location
    Funk, Ohio

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    And any weight added ahead of or behind the axles increases the polar moment of inertia more than the same weight added to or between the axles, making the tractor less prone to rotating on the vertical axis -- yaw or pitch. Adding weight outside the longitudinal centerline makes it less prone to roll, or rotation along the longitudinal axis (Front to Rear). Call it the dumbell effect -- a weight lifting bar with the weights in the center is much easier to rotate than the same bar and weight combination with the weights on the ends of the bar.

    Both these statements are from a stationary POV. Once the tractor starts rotating in any of the aforementioned manners, the same weight that made it resistant to start rotating will also act to make it continue. Hence the rationale for doing things slowly when you have the slightest doubt about stability.

    As has been said many times here, what you really want is a good balance between power, traction and weight. Too much weight steals power and also makes the tractor handle sluggishly. Not enough weight keeps you worried about falling over or results in too little traction.
    Rich
    300 hours on the DX29, 850 on the JD 240 and too many to count on the Cadet
    Funk, Ohio

  8. #18
    Super Star Member Egon's Avatar
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    Aug 2001
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    Nova Scotia, Canada

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    From what I read we should be looking at Dynamic Statics.
    Egon
    50 years behind the times
    Livin in a
    Worn out skin bag filled with rattlin bones

  9. #19
    Veteran Member jimmysisson's Avatar
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    Jul 2005
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    W.Mass
    Tractor
    1993 NH 2120 (the best), 1974 MF 135 (sold, but solid), 1947 Farmall A (bought, sold, bought back, sold again), 1956 MH50 lbt (sold, in 1980, darn it)

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    Quote Originally Posted by whodat90
    Excellent post which brings up an interesting point about counterweighting to keep weight (traction, braking) on the rear tires. What about putting, say, an 800lb load in that loader and running the numbers again? Also, an important point about why to add weight to the rear tires: Counterweights on the 3pt hitch hang from the tractor. The tractor hangs from filled tires. You get all the weight at almost no stress to the tractor. Sprung weight vs. unsprung weight.
    whodat
    ************
    Unsprung weight is a term used in auto sports, refers to the wheels, tires, and part of the suspension: the parts not supported/controlled by the springs and shocks. Less unsprung = more control by the car/driver, and is desirable. More unsprung = bad. Tractors = all unsprung = bad [as far as racing is concerned]. Springs on a tractor = bad for every other reason + use. Tractor racing, now I don't know....
    Jim
    "Anything worth doing is worth doing slowly" Mae West

  10. #20
    Silver Member
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    Jul 2006
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    Location
    Northeast South Dakota
    Tractor
    AGCO ST30X

    Default Re: Tractor ballasting, weight distribution & free body diagrams

    i am a a mere Industrial Engineer but am thoughly impressed with your knowledge of freebody diagrams and statics and dynamics.

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