[AT] weighted tires or not???

Jim Becker mr.jebecker at gmail.com
Wed Sep 4 08:19:59 PDT 2019


Adding weight on the rear wheels (wheel weights or loading with fluid) will shift the CG back but have no effect on the actual weight on the front axle.  However, adding weight at the back of the tractor (weight box, mounted implement, etc.) will reduce the absolute weight on the front axle, shifting the same amount to the rear axle.  For example, if the tractor has a 6 foot wheelbase and you hang 100 pounds 3 feet behind the rear axle, you will take 50 pounds off the front axle and add 150 to the rear.

Jim Becker

From: Dean Vinson 
Sent: Wednesday, September 04, 2019 5:51 AM
To: 'Antique Tractor Email Discussion Group' 
Subject: Re: [AT] weighted tires or not???

Dean VP, completely agree—the loader moves the COG forward as you said, and rear weights move it back rearward and downward as Steve had said.  Only quibble I’d add is that you may have meant to say adding ballast in the rear reduces “the relative proportion of” weight on the front axle, not the absolute weight on the front axle.

 

I’ve never rolled a tractor but have a little sub-compact utility tractor with a mower deck and loader.  I should get a rear counterweight for the 3-point hitch (or an implement, as you’ve done) for use with the loader, but just having the mower deck on helps a lot.  (Although it can be in the way sometimes, limiting the usefulness of the loader).   But without at least the mower deck on, the loader is all but useless… little tractor is just too tippy.

 

Dean Vinson

Saint Paris, Ohio

 

 

From: AT [mailto:at-bounces at lists.antique-tractor.com] On Behalf Of deanvp at att.net
Sent: Wednesday, September 4, 2019 2:04 AM
To: 'Antique Tractor Email Discussion Group' <at at lists.antique-tractor.com>
Subject: Re: [AT] weighted tires or not???

 

Steven

 

Here is why I think adding rear counter weight to a tractor with a loader helps stability against roll-over.

 

When a loader is added to a tractor  the COG moves forward. With a load in the bucket it moves further forward almost over the front axle causing less traction or weight on the rear axle/tires.  Note: adding ballast in the rear reduces weight on the front axle with more on the rear.  Most of the roll over stability comes from the rear tires.  One does not want the tractor stability coming from a rotating WFE or a NFE.  The rear wheels need to have a dominate role. This may be an intuitive response but I think the physics will verify it. 

 

Dean VP

Snohomish, WA 98290

 

From: AT <at-bounces at lists.antique-tractor.com> On Behalf Of Stephen Offiler
Sent: Tuesday, September 3, 2019 5:19 AM
To: Antique Tractor Email Discussion Group <at at lists.antique-tractor.com>
Subject: Re: [AT] weighted tires or not???

 

In 3-dimensional space, the CG of a tractor is likely to be very close to the center in terms of left-right; closer to the rear in terms of front-back; and some height from the ground.  When you add ballast to the tires it does not change that left-right CG location (assuming you add ballast equally to both rears), and moves CG even farther to the rear and closer to the ground.  It is intuitively clear that a tractor on the verge of a side rollover will be aided by weight added to the uphill side.  But from a free body diagram perspective, the difference comes from the changes in CG rearward and downward.

 

SO

 

 

On Tue, Sep 3, 2019 at 7:56 AM Jim Becker <mr.jebecker at gmail.com> wrote:

  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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