fill ag tires @ 50% or 75% for lowest Vertical Center of Gravity (VCG)?

[mtsman2]

Lets talk center of gravity. Lets start with background info. from someone better trained than me:

"Every three dimensional object has three centers of gravity one for each dimensional plane. There is a horizontal center of gravity (HCG), a vertical center of gravity (VCG), and a lateral center of gravity (LCG). When applying this to a truck chassis, whether you realize it or not, we already deal quite extensively with the horizontal center of gravity. We do this by the wheelbases we choose, the body lengths we use and the placement of those bodies and added equipment on the chassis in question. A shift in the HCG manifests itself as a change in the percentage of the vehicles total weight carried on each axle.

Lateral centers of gravity are something that we rarely have to deal with. That is due to the fairly symmetrical layout of most truck chassis and the attendant bodies and equipment attached to them. Think of a LCG as a side-to-side weight distribution.

That leaves only one more plane the vertical one. The vertical center of gravity is normally expressed as being 度 number of inches above level ground. This is the midpoint of the vertical distribution of the weight of the unit. The vertical center of gravity has a direct correlation to vehicle rollover stability. The higher the VCG, the higher the rollover propensity."

How does loading of tires effect on VCG?
Standard loading of rear Ag tires fills to max amount while valve stem is at 12noon. This is about 75% fill according to the published literature. What if we only filled the rear Ag tires to about 50% by placing the valve stem at 3pm/9pm? (this is also filling the rear Ag tire to approximately the centerline of the rear axle).
IMO, the VCG on tractors is somewhere near or just above the centerline of the rear axle. That is an opinion and should vary but I just DONT see the VCG nearing the top of a rear ag wheel. YET, standard filling of ag tires is well above the centerline of the rear axle up to the top of the rear wheel.

In your opinion, do you think filling rear Ag tires to only 50% (valve stem @ 3pm/9pm) would be better for maintain VCG/less chance of rollover? I suspect track width at with Ag tires may play a role in the determination/calculation? Does anyone have a formula to calculate the answer?


Simplified 2 schools of thought:
1) more total weight in the tire is going to create a better ballast/weight vector on a slope to prevent a rollover...even if the fluid weight comes in above the VCG.
2). filling the tire to 50% with the valve stem positioned at 3pm/9pm (about the centerline of rear axle) will still add ballast/vector weight (but not as much) HOWEVER the fluid weight will never POTENTIALLY be above the VCG and overall will actually create a greater lower VCG.


i looked back about a year and did not see a post in this area. If it missed it, my apologies, could someone reply with a link to it.

 

[BrokenTrack]

Lets talk center of gravity. Lets start with background info. from someone better trained than me:

"Every three dimensional object has three centers of gravity one for each dimensional plane. There is a horizontal center of gravity (HCG), a vertical center of gravity (VCG), and a lateral center of gravity (LCG). When applying this to a truck chassis, whether you realize it or not, we already deal quite extensively with the horizontal center of gravity. We do this by the wheelbases we choose, the body lengths we use and the placement of those bodies and added equipment on the chassis in question. A shift in the HCG manifests itself as a change in the percentage of the vehicles total weight carried on each axle.

Lateral centers of gravity are something that we rarely have to deal with. That is due to the fairly symmetrical layout of most truck chassis and the attendant bodies and equipment attached to them. Think of a LCG as a side-to-side weight distribution.

That leaves only one more plane the vertical one. The vertical center of gravity is normally expressed as being 度 number of inches above level ground. This is the midpoint of the vertical distribution of the weight of the unit. The vertical center of gravity has a direct correlation to vehicle rollover stability. The higher the VCG, the higher the rollover propensity."

How does loading of tires effect on VCG?
Standard loading of rear Ag tires fills to max amount while valve stem is at 12noon. This is about 75% fill according to the published literature. What if we only filled the rear Ag tires to about 50% by placing the valve stem at 3pm/9pm? (this is also filling the rear Ag tire to approximately the centerline of the rear axle).
IMO, the VCG on tractors is somewhere near or just above the centerline of the rear axle. That is an opinion and should vary but I just DONT see the VCG nearing the top of a rear ag wheel. YET, standard filling of ag tires is well above the centerline of the rear axle up to the top of the rear wheel.

In your opinion, do you think filling rear Ag tires to only 50% (valve stem @ 3pm/9pm) would be better for maintain VCG/less chance of rollover? I suspect track width at with Ag tires may play a role in the determination/calculation? Does anyone have a formula to calculate the answer?


Simplified 2 schools of thought:
1) more total weight in the tire is going to create a better ballast/weight vector on a slope to prevent a rollover...even if the fluid weight comes in above the VCG.
2). filling the tire to 50% with the valve stem positioned at 3pm/9pm (about the centerline of rear axle) will still add ballast/vector weight (but not as much) HOWEVER the fluid weight will never POTENTIALLY be above the VCG and overall will actually create a greater lower VCG.


i looked back about a year and did not see a post in this area. If it missed it, my apologies, could someone reply with a link to it.

I dug 700 cubic yards out of my gravel pit last year with my little Kubota tractor with no fluid filled tires and managed just fine.

If a person can dig, dump, haul, load, fill and move that much gravel, 2200 times in severe service in rapid succession, I think it has more to do with operator skill in preventing an upset tractor, failing to get weight transfer, ineffective tractive effort, and poor break out forces, than having fluid filled tires.

But, get a tractor stuck in the mud with fluid filled tires, and a person will readily understand the kinetic energy involved when "rocking a tractor out of the mud", induces kinetic forces that far exceed the shear strength of high strength gears in the rear end. In other words, they will find out what is involved in changing the rear end out of their tractor.

In Grandpa's day, yeah we used fluid-filled tires, but none of our tractors have that any more. It just does not make any sense too; the bad outweighs the good by about ten to one.

 

[hosspuller]

50% or 75 % fill is small potatoes. If you're going to fluid fill, use enough to cover the rim. Even with antifreeze, exposing the wet metal rim to air in the tire is asking for corrosion. I just bought a tractor with fluid fill. Increasing the width did more for stability than the extra weight. (I have an almost identical tractor with the same unfilled tires.)

 

[s219]

The question can be answered with statics analysis and diagrams of all the forces and moments. It will be highly dependent on exact specs and measurements though. Not something with a "general" answer.

 

[RickB]

The speed at which the tilt angle changes while the tractor is moving and the related inertia is never mentioned or accounted for. Dropping the downhill rear wheel in a hole at 6 mph can end very differently than the same tractor and the same hole at .5 mph. This omission, so far as I am concerned, renders all the theoretical discussions somewhat moot.

 

[s219]

The other problem is that the fluid can move as the tractor tips, potentially making things worse.

 

[BrokenTrack]

The question can be answered with statics analysis and diagrams of all the forces and moments. It will be highly dependent on exact specs and measurements though. Not something with a "general" answer.

It is called Paralysis by Analysis and it permeates all of society unfortunately.

But if you want to get technical, to me; you are going about it all wrong. Fluid filled tires might lower the center of gravity somewhat, but that is about all it does.

If you want to get into physics, it is waste of time to discuss fluid-filled tires because the net gain is so low. A tractor owner has a very limited space in which to add weight (fluid), the ability to make that area more dense with liquid is very limited, and it is in a very non-effective area...which is right over the rear axle.

If a person wants to be effective, they want to get weight out PAST the rear axle, this is called leverage, and the weight transfer shifted past the rear axle is going to counteract the weight in the bucket in proportion cubed to the distance moved from the rear axle. It is as simple as, 250 pounds of weight six feet past the rear axle is going to be more effective at counteracting the weight in the front bucket, than 500 pounds of weight in the rear tires.

Look at a tower crane. To lift heavy loads they do not fill the tower base with water, they shift weight further aft to counteract the load.

It is not rocket science, and with adding counterweight to the back, there are so many more options. A tractor owner can add more weight, change the shape of the counterweight, use denser materials for greater weight, or shift it further aft more.

We used to fluid-fill tires too, but it is a very expensive way to get minimal results.

 

[mtsman2]

In Grandpa's day, yeah we used fluid-filled tires, but none of our tractors have that any more. It just does not make any sense too; the bad outweighs the good by about ten to one.

LOL. good work with all the dirt you have moved with the kubota. Thanks for reply and staying on topic.

 

[mtsman2]

50% or 75 % fill is small potatoes. If you're going to fluid fill, use enough to cover the rim. Even with antifreeze, exposing the wet metal rim to air in the tire is asking for corrosion. I just bought a tractor with fluid fill. Increasing the width did more for stability than the extra weight. (I have an almost identical tractor with the same unfilled tires.)

I agree its small potatoes. Coming out to about #100 difference on each tire for me. But on a #3700 tractor + loader that's only about 5% so it is still small potatoes. Was curious more than anything else.
Point noted about potential corrosion. Not sure to which unit you are referring but this is for a new Kioti. But, I have widened my F22D via spacers and the difference was noticeable.

 

[mtsman2]

The question can be answered with statics analysis and diagrams of all the forces and moments. It will be highly dependent on exact specs and measurements though. Not something with a "general" answer.

TY S219! I knew someone had experience in this area. I do wish there was an easier to calculate answer.