arthr31
Platinum Member
Hey, no problem, it was missed on me, but I'm an overly serious kinda guy... Gee, I should relax a bit! :-D
YM 2000 - Roll Over
- Thread starter sls
- Start date
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Gizmo is bang on, think about it, if you fill your tyres above the axle you are adding wieght above the COG, therefore it will be more tippy on steeper hills. Simple as that.
BUT
Filling your tyres all the way up will provide more weight so on lesser hills it will be more stable.
Think about it this way, you add lead low down below the axle (filling tyres below axle) - more stable right, weight below the COG. Then you add weight above the axle (filling tyres all the way up) - the tractor is more stable as long as the weight is acting almost vertically downwards. If you drive the tractor up onto a steeper hill the weight up high will try to pull the tractor over, making it less stable.
So in effect all of you are right, but in different circumstances. If you want to try this out, get a toy tractor and use plastercine in place of the lead weights I described above (add some the either side by the wheel to make it more realistic like filled tyres.
So to conclude - Im NOT saying anyone is wrong, so dont eat me, but it depends on the circumstances as to how you should do it.
PS, My tyres are filled 3/4 up so I'm sitting on the fence /forums/images/graemlins/wink.gif
BUT
Filling your tyres all the way up will provide more weight so on lesser hills it will be more stable.
Think about it this way, you add lead low down below the axle (filling tyres below axle) - more stable right, weight below the COG. Then you add weight above the axle (filling tyres all the way up) - the tractor is more stable as long as the weight is acting almost vertically downwards. If you drive the tractor up onto a steeper hill the weight up high will try to pull the tractor over, making it less stable.
So in effect all of you are right, but in different circumstances. If you want to try this out, get a toy tractor and use plastercine in place of the lead weights I described above (add some the either side by the wheel to make it more realistic like filled tyres.
So to conclude - Im NOT saying anyone is wrong, so dont eat me, but it depends on the circumstances as to how you should do it.
PS, My tyres are filled 3/4 up so I'm sitting on the fence /forums/images/graemlins/wink.gif
Paddy
Veteran Member
Mith,
I find fault in your math. This is simple moment problem
mass Up hill wheel=U
mass Lower wheel=L
(Assume mass of U and L are =)
distance to pivot of up hill wheel= du
distance to pivot of down hill wheel= dl
As the tractor begins to raise the wheel......
UxdU>LxdL
500lbx 48"> 500lbx 3"
This is because the down hill tire is the pivot. The up hill mass is the same but has the entire axel length as a lever. Again at first point uphill tire is raised, the down hill tire mass is just a few inches from the pivot. The Up hill mass is 48"+ off the pivot. You can draw a diagram as well. Draw a wide H. The wheel mass can be centered at the hub. The engine/tranny CG needs to be above axel.
Once all the engine/tranny mass cross the plumb line it's all over. The trick here is the distance the masses are from the pivot. hence wide front ends and wide rear stance
Also with the valve stem located where it is, I'll guess 75% is about max in terms of volume
Patrick
I find fault in your math. This is simple moment problem
mass Up hill wheel=U
mass Lower wheel=L
(Assume mass of U and L are =)
distance to pivot of up hill wheel= du
distance to pivot of down hill wheel= dl
As the tractor begins to raise the wheel......
UxdU>LxdL
500lbx 48"> 500lbx 3"
This is because the down hill tire is the pivot. The up hill mass is the same but has the entire axel length as a lever. Again at first point uphill tire is raised, the down hill tire mass is just a few inches from the pivot. The Up hill mass is 48"+ off the pivot. You can draw a diagram as well. Draw a wide H. The wheel mass can be centered at the hub. The engine/tranny CG needs to be above axel.
Once all the engine/tranny mass cross the plumb line it's all over. The trick here is the distance the masses are from the pivot. hence wide front ends and wide rear stance
Also with the valve stem located where it is, I'll guess 75% is about max in terms of volume
Patrick
But if there is more mass higher, therefore the CofG is higher, then the point of no return, a roll over, is on less of an angle. The lower the weight the steeper angle the you go on, that is a fact.
Diagram, shows that with less fluid in your tyres the CofG of the tyre is further uphill, so tractor is more balanced.
You are right in what you say, but, if the tyres were less full the moment would be even further away from the CofG, therfore less likely to tip.
It isnt a simple moments thing, the weight of the upper wheel does offset the weight of the lower wheel, but the point is it will offset it just as well, and FURTHER into the roll before it crosses that piviot than if there was more weight up higher. All you are saying is bang on, its just that the basic fact, with less fill the CofG is lower so the tractor can tip further before it crosses the plumb and rolls.
On 2 tractors exactly the same the CofG will be higher on the one with tyres filled all the way up, therfore it will go on less of a slope before it rolls.
Yes, you are right about only being able to fill it to 75%, unless you put it in under pressure
Diagram, shows that with less fluid in your tyres the CofG of the tyre is further uphill, so tractor is more balanced.
You are right in what you say, but, if the tyres were less full the moment would be even further away from the CofG, therfore less likely to tip.
It isnt a simple moments thing, the weight of the upper wheel does offset the weight of the lower wheel, but the point is it will offset it just as well, and FURTHER into the roll before it crosses that piviot than if there was more weight up higher. All you are saying is bang on, its just that the basic fact, with less fill the CofG is lower so the tractor can tip further before it crosses the plumb and rolls.
On 2 tractors exactly the same the CofG will be higher on the one with tyres filled all the way up, therfore it will go on less of a slope before it rolls.
Yes, you are right about only being able to fill it to 75%, unless you put it in under pressure
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Paddy
Veteran Member
On my tractor, the main tractor CG will cross the plumb line before the weight of the up hill tire will. Thus, all ballst in tires will help because mass x distance to pivot. You can see this by drawing two diagrames, one very wide and one narrow. On the wide diagrame you see the tire never gets close to hurting the balance.
You can prove this by just working with the axel and tires with out a tractor. I'll flip your empty set far sooner than you will be able to flip my full set. This is based on Cosine of the angle. Even at 45 deg, 0.707 of the weight is pushing down.
This is a case of ratios, CG to width. The CG of the axel is centered...on the axel. The axel wheel assembly is far beter than the tractor alone, because we all know the CG of the tractor is above the axel.
My tractor has wheel spacing at 56" and CG is approx 36".
What is your wheel spacing and CG height?
physics it's not just fun..it's the Law
You can prove this by just working with the axel and tires with out a tractor. I'll flip your empty set far sooner than you will be able to flip my full set. This is based on Cosine of the angle. Even at 45 deg, 0.707 of the weight is pushing down.
This is a case of ratios, CG to width. The CG of the axel is centered...on the axel. The axel wheel assembly is far beter than the tractor alone, because we all know the CG of the tractor is above the axel.
My tractor has wheel spacing at 56" and CG is approx 36".
What is your wheel spacing and CG height?
physics it's not just fun..it's the Law
bruce1966us
Platinum Member
Well it is not the LAW when you fiqure in rocks, holes, stumps, etc. I'm by no means argueing, just throwing a curve ball /forums/images/graemlins/grin.gif
Everyone who is saying 50% fill is correct is making a huge INCORRECT assumption.
You are assuming that the center of gravity of the tractor AS A WHOLE is at rear axle height.
The math is simple but will differ with each tractor and ALSO with the angle of tractor. When sitting flat, weight that is below the center of gravity point is beneficial in stability.
When on an angle, then weight on one side acts as a lever around the COG point, so fluid higher than 50% in the tire will still be beneficial. True.. it may be higher than the center of gravity when on an angle, but acts as a lever around the pivot point to add stability.
You are assuming that the center of gravity of the tractor AS A WHOLE is at rear axle height.
The math is simple but will differ with each tractor and ALSO with the angle of tractor. When sitting flat, weight that is below the center of gravity point is beneficial in stability.
When on an angle, then weight on one side acts as a lever around the COG point, so fluid higher than 50% in the tire will still be beneficial. True.. it may be higher than the center of gravity when on an angle, but acts as a lever around the pivot point to add stability.
Paddy
Veteran Member
Mith,
I didn't see your diagram before the reply. The diagram has an error. vectors
Let's break the mass in to 3 locations; 1 tractor, 2 up hill wheel an 3 lower wheel. CG of those masses; The wheels are easy if we say at the hub and the tractor at say 60% the height of the wheel or just below the seat.
Now let's establish the pivot, the lower set of tires.
Using your diagram, draw vertical vectors pointing down at each of the 3 mass locations. assign weight to each vector. Now the most important part...measure the horizontal distance the vector(s) are from the pivot. Multiply them by the masses and assign them pos numbers for rotating CW and neg for CCW with regards to the pivot.
now create a simple table where you decrease the mass in those tires and lower the efective vector. As you remove weight, you lose stability.
At 45 or any degree the up hill tire is further away from the pivot. The tractor CG has long passed the vertical line above the pivot befor the up hill mass will cross.
I didn't see your diagram before the reply. The diagram has an error. vectors
Let's break the mass in to 3 locations; 1 tractor, 2 up hill wheel an 3 lower wheel. CG of those masses; The wheels are easy if we say at the hub and the tractor at say 60% the height of the wheel or just below the seat.
Now let's establish the pivot, the lower set of tires.
Using your diagram, draw vertical vectors pointing down at each of the 3 mass locations. assign weight to each vector. Now the most important part...measure the horizontal distance the vector(s) are from the pivot. Multiply them by the masses and assign them pos numbers for rotating CW and neg for CCW with regards to the pivot.
now create a simple table where you decrease the mass in those tires and lower the efective vector. As you remove weight, you lose stability.
At 45 or any degree the up hill tire is further away from the pivot. The tractor CG has long passed the vertical line above the pivot befor the up hill mass will cross.
EFC
Veteran Member
The reason the tires are filled is to limit sloshing. The sloshing of large tires can actually turn the tractors over on its own. We had a Farmall that if you used the highway gear going down long grades (I was a bit dumber when I was a teenager) if you hit a dip in the road the fluid would start to come over the top of the axel and actually lift the rear tires off the ground. The bouncing action would get worse and worse till it was out of control.
I was baleing hay with that same tractor on a gradual side hill, nothing special, and the down hill tire fell into a dip and bounced right out. The fluid was sloshing so bad I didn’t know if it would roll over or not. It was a coin toss for a few seconds. After that we filled the rears all the way up.
The difference was immediately noticeable. Sorry I couldn’t help with the math
Buck
I was baleing hay with that same tractor on a gradual side hill, nothing special, and the down hill tire fell into a dip and bounced right out. The fluid was sloshing so bad I didn’t know if it would roll over or not. It was a coin toss for a few seconds. After that we filled the rears all the way up.
The difference was immediately noticeable. Sorry I couldn’t help with the math
Buck
Paddy
Veteran Member
You are correct there, the movement of the mass can cause big problems. We see it often in trucking.
