[AT] weighted tires or not???

[Stephen Offiler]

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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