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

[RickB]

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

It is commonly known as pucker factor analysis.

 

[mtsman2]

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.

yep, agree that speed dependent related inertia creates sudden moment arm changes which can affect the VCG. I did not mention momentum nor related inertia because I was not looking for that information. Also, the last time I checked if you removed related inertia you can STILL discuss static VCG. I am trying hard to be nice and keep on topic.

 

[mtsman2]

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.

So now you do use fluid filled tires and now it DOES lower the VCG (even if minimally). Thank you.

Your leverage and counterweight example is great. You have given a great example that is more of Horizontal center of gravity...weight over the axles as described in the very first post. Thank you.

I was looking for more input on VCG. This was not presented for loader ballast via tire loading. As you shared, we can all easily install any of our #250-#600 attachments to counteract the weight of a full loader.

This is for discussing/potentially decreasing tipover on a slope while being static via 2 tire loading options. Please read the first post again. Hosspuller is correct that the change would be minimal. But it was something I wished to explore via others feedback who may have solved the same dilemma.

 

[ruffdog]

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

We have to remember that, with COVID around, many people have to stay home and pass the time somehow. For some people, solving simple problems mathematically may be a good pastime for them.

 

[CobyRupert]

IMHO, it’s pretty simple.
Weight added below the natural COG lowers the COG.
Weight added above the COG raises the COG.

So ballast filled above the axle gives a higher COG than if tire was less filled.
.....but as other mention it has the advantages of covering rim from air and of more rear weight for rear traction when using loader or in general.

 

[mtsman2]

IMHO, it’s pretty simple.
Weight added below the natural COG lowers the COG.
Weight added above the COG raises the COG.

So ballast filled above the axle gives a higher COG than if tire was less filled.
.....but as other mention it has the advantages of covering rim from air and of more rear weight for rear traction when using loader or in general.

TY CR. These were my generalized assumptions too. I am sure it occurs but I have never met someone who only fills the rears to 50%. They all fill it right to the valve stem at 12noon. So it may be a mixed bag of positive and potentially negative effects. Many thanks for understanding the question.

 

[Hay Dude]

As a farmer, for decades everyone used ww fluid and filled about to top of rim. Every used tractor I bought had rims loaded this way. I removed all fluids and replaced with cast center rims or wheel weights.
I always had a crude vision of a 途otating wheel weight? So roughly speaking, you壇 bolt a circular 途acetrack to the center of your rim not unlike a traditional wheel weight. Inside the circular race track, you would have a 1/2-circle weight which would always be at the bottom half of the wheel to keep it below COG.
Probably wouldnt work-something about wheel balancing at high speeds or how to keep it lubricated, but would always keep weight below wheel hub instead of surrounding it like a wheel weight and have none of the drawbacks of fluids.

 

[ruffdog]

Why has the max angle of the slope not been mentioned? Wouldn't that be part of the equation?

 

[BrokenTrack]

Why has the max angle of the slope not been mentioned? Wouldn't that be part of the equation?

My understanding was, maximum slope with a wheel tractor is around 18 degrees. With boom mowers and stuff you can radically change that, or with articulated tractors you can negotiate steeper slopes obviously, but as a general rule of thumb, 18 degrees start engaging the "pucker factor".

But even here, loaded rear tires is not a huge part of the equation. Again it is physics...

The limiting factor of a tractor tipping over is the amount of angle the FRONT AXLE oscillates. Sure, we have al side loaded the bucket, stopped quick, the tractor came up on three wheels, but never went over.

Why?

It rolled easily to that point because the front axle pivoted until it hit the frame. Again, physics: three points in space make a plane.

The second that happened though, now the tractor has four points to overcome to keep going over, and unless excess speed, or a loader bucket is up to high, or a down hill tire hits a gopher-hole, the tractor has to do A LOT to flip over.

Loading tires does not really help with the center of gravity because those fluid-filled tires are tilted at 18 degrees or more too. Remember: if your front axle is hitting the frame, then your front axle has stayed level with the terrain (18 degrees), but if your high, rear tire is off the ground, your rear-end is going to be several degrees steeper than the hill you are on. That means the fluid at the top, on both tires, is located DOWNHILL by 18 degrees or more. So some of that fluid filled weight is working against you, not for you, in trying to force the tractor to roll over.

But it takes an awful lot to roll a tractor once that front axle hits the frame. A whole new set of physics takes over.

 

[BrokenTrack]

As a farmer, for decades everyone used ww fluid and filled about to top of rim. Every used tractor I bought had rims loaded this way. I removed all fluids and replaced with cast center rims or wheel weights.
I always had a crude vision of a 途otating wheel weight? So roughly speaking, you壇 bolt a circular 途acetrack to the center of your rim not unlike a traditional wheel weight. Inside the circular race track, you would have a 1/2-circle weight which would always be at the bottom half of the wheel to keep it below COG.
Probably wouldnt work-something about wheel balancing at high speeds or how to keep it lubricated, but would always keep weight below wheel hub instead of surrounding it like a wheel weight and have none of the drawbacks of fluids.

That is a nice idea.