[AT] weighted tires or not???

[Jim Becker]

The added 500# on the high side has more effect than the 500# on the low side.  It is farther away horizontally from the bottom of the low side rear tire (or the magic triangle/trapezoid) and thus has more leverage.  As far as it “having a greater effect than any change in CG”, it is the same thing.  Looking at the 500# by itself is just selecting one component of the CG to look at (a valid way to look at it).

Adding fluid to the tires definitely lowers the CG.  How much depends on a bunch of factors, including how tall the tires are, how high the CG is to begin with and the relative weight of the fluid vs. the weight of the tractor.  The taller the tractor, the more effect it has.  When we first started using mechanical grape pickers (1960s), many of them were built on a very high clearance tractor (6 feet+ under the axles).  The things were plenty heavy enough as delivered, but everyone loaded the tires to help the stability.

Jim Becker

From: Dennis Johnson 
Sent: Monday, September 02, 2019 5:46 PM
To: Antique Tractor Email Discussion Group 
Subject: Re: [AT] weighted tires or not???

Static rollover happens when the CG moves outside of the pivot point which is the bottom of the downside tire (or tires of pivot is against stop). As long as the CG is “inside” of the down side rear tire the vehicle will not roll. As soon as the CG moves outside of the pilot point the unit will rollover. 
Dynamic rollover when turning at speed changes things because it adds centrifugal force to help shove the CG sideways and make the unit roll sooner.

With weighted tires, the downside tire has an extra 500# outside of the pivot point trying to tip it, in addition to the 500# or the upside tire holding it back. 

Dennis



Sent from my iPad

On Sep 2, 2019, at 5:22 PM, Howard Pletcher <hrpletch at gmail.com> wrote:


  Wouldn't the extra 500# or so holding the high side down have a greater effect than any change in CG?  It seems it would be more stable.

  Howard

  On Mon, Sep 2, 2019 at 5:54 PM Dennis Johnson <moscowengnr at outlook.com> wrote:

    The weighted tires would lower the center of gravity slightly. Assuming the tires were 100% full the CG of the added fluid would be on the axle CG. If less than 100%, then the CG would be slightly lower. The CG of most tractors will be slightly above the axle center. Tractors with offset final drives would have CG a little higher than those with the final drive in line with the engine crankshaft. Combining the CG of the tires and tractor would lower the overall CG a little bit, making the tractor more stable.
    Adding low mounted implements or weights would change this.

    Dennis

    Sent from my iPad

    > On Sep 2, 2019, at 2:37 PM, John Hall <jtchall at nc.rr.com> wrote:
    > 
    > All this talk about wide front vs. narrow front got me wondering about something else. Are tractors with fluid filled rears more stable on hills or in quick maneuvering on uneven ground? The reason I ask is that I replaced the tires on a IH utility tractor we have had since new (1972 454). It has over 8,000 hrs and we have always had weighted tires on it. Well I didn't have time to fill the tires with fluid before I began using it this spring. So far I am liking the less weight for treading on wet spots in fields. I recently reduced the air pressure (it was at 25, I dropped it to 20) because it was shaking me to death while spraying a field. The only time the loss of weight has been an issue is moving one load of hay--it was digging pretty bad. We do all of our bushogging with this tractor so there are quite a few banks and hillsides to get into. Wonder if it would be more stable with the fluid in?
    > 
    > John Hall
    > 
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