Wheel VS Frame weighs...what's up?

[Henro]

Wheel VS Frame weighs...what\'s up?

I am having great difficulty understanding why a tractor manufacturer would recommend NOT loading tires or using wheel weights, but WILL recommend weights hung off the frame. /forums/images/graemlins/frown.gif

Does anyone have an explanation for this? /forums/images/graemlins/confused.gif

It would seem to me that weight that was part of wheel itself, would be a plus, not a negative, as the ground would carry that weight, rather than the axles for the most part.

I realize there are forces that would be greater with heavier wheel/tire, but tractor wheels don't really rotate very fast.

If the wheel were suspended on a shaft like a fan blade, then I could understand extra wheel weight as being undesirable, but a wheel is not a fan blade. /forums/images/graemlins/smile.gif

It just seems like a heavy wheel would be no worse than the same amount of weight being put on the frame. And might be better. A specific example would be my Kubota BX2200.

I am thinking of buying a set of bar tires to use in winter and if I am doing something in the dirt/mud with that tractor. I might get them foam filled, as that adds weight and punctures will be eliminated. It is my understanding that this would be frowned upon by Kubota. /forums/images/graemlins/mad.gif

I am not good at following blind orders, but I am good at following good reasons! /forums/images/graemlins/crazy.gif

Anybody have a reason/explanation/analysis/experience that shows why I should not add weight WITHIN the tires, while I CAN hang a weight box on the back and suitcase weights on the front without problem? /forums/images/graemlins/confused.gif

Can someone help this numb mind see the light?

 

[gotrocks]

Re: Wheel VS Frame weighs...what\'s up?

Good Morning Henro,
I've read many of your posts and you have come up with many interesting questons and answers.

Now my first though on this question, is that assuming a wheel weight is "balanced" on the wheel that would not lower the CG as much as a frame weight, since half of the wheel weight would be above the axle at all times.

I agree that frame wt. would increase load on axles, so I guess my decision as to which location of weight would be determined as to wanting a lower CG or just more traction.

Happy Valentine's Day!

I got mine, hope you got yours.

 

[Bob_Skurka]

Re: Wheel VS Frame weighs...what\'s up?

Henro, I have NO CLUE as to why some of the manufacturers (especially Kubota) say not to weight the wheels or load the tires. I have been baffled by the same question. I didn't want to pay the outrageous prices for genuine Kubota weights for my B2910 so there is 350 pounds of scrap iron on the frame. In retrospect, loading the rears would have put the weight were I really wanted it. Last year I bought a little New Holland TC24 to get into some tight spots and for 3pt work, I added EZ-Weights with 100 pounds of bar stock to the front wheels (50# on each wheel) and wish I would have added a bit more (that may be the next project?).

I deduced that the wheel weights allowed the ground the carry the weight and frame weights forced the axle to carry the weight. I just did it. I am happy with it. I would do it again.

 

[Bob_Skurka]

Re: Wheel VS Frame weighs...what\'s up?

Gotrocks. . . I would disagree with your assessment about lowering the Center of Gravity.

The center line of the wheel is lower than the frame. A typical "suitcase weight" that hangs on the frame is partially above and partially below the centerline of the frame. But since the frame is above the center line of the wheel, it places the weight higher.

On the other hand, suitcase weights mouted on the front frame put the weight farther forward, which helps balance a heavy rear implement better than front wheel weights (of equal weight) would. But this also increases the overall lenght of the tractor, which can be a drawback if your garage space is limited.

Rear weights, in the form of a weight box, would allow you to adjust the height of the weight by simply adjusting the lift on your 3pt hitch, but that also adds considerable lenght to the tractor which can make it very difficult to work in trees or tight spaces.

 

[ronjhall]

Re: Wheel VS Frame weighs...what\'s up?

Henro

I believe it has to do with centrifugal force. When the tires and wheels get moving the liquid inside starts rotating at the same speed as tire after some acceleration time. This acceleration put a load on the HST. When tractor is slowed down the liquid continues to rotate, which also puts an extra load on the HST.

Someone may be able to explain it better than I can. /forums/images/graemlins/tongue.gif

 

[strez]

Re: Wheel VS Frame weighs...what\'s up?

Weight on a wheel affects the wheel's rotational moment of inertia. The moment of inertia of a system about some rotational point is the measure of an object's resistance to a change in the object's angular acceleration due to the action of a torque and is dependent on how the weight is distributed on the wheel. The common wisdom is rotational weight counts twice that of non-rotational weight. Read any cyclist magazine or book -- when these folks are trying to shave ounces from their bikes, the first place they look is on the wheels -- more "bang for the buck", if you will.

How does this relate to a tractor? Simple. More weight on the wheel requires more torque (2x is a good estimate) to get the tractor moving. Light wheels and wheels with their mass distributed close to their axles have low moments of inertia, and they will accelerate easily. In contrast, heavy wheels and wheels with their mass distributed far from their axles require a large torque value to accelerate.

Using more torque every time the tractor accelerates and more braking power every time the tractor decelerates results in more wear and tear on the drivetrain. This is why, I believe, the manufacturers recommend against wheel weights.

 

[Bob_Skurka]

Re: Wheel VS Frame weighs...what\'s up?

RonJHall & Strez . . . I absolutely buy into your arguements if we limit the discussion to high speed tire rotation. And I don't discount the physics for low speed rotation becuase the math is going to be the same, however, SOME tractor manufacturers DO recommend loading tires and SOME advocate using wheel weights OR suitcase weights.

So, while a centerfugal forces and inertia may make a gyroscope type effect on a fast spinning wheel that has weights added to it, when a tractor is typically moving between 2 and 6 miles per hour, I think the arguement falls apart.

When SOME manufacturers allow it and SOME do not, then might one conclude that the HST of one brand is inferior to the HST of the other? (yet in real life both seem to provide decades of reliable service)

So my NH allows for loading the tires, it says so in the manual, does that mean that the NH drive train is capable of handling the extra torque? And my Kubota, which recommends only static weights on the frame, is not capable of dealing with extra torque caused by loaded tires or solid weights on the wheels?

I would agree that there will be some added strain on the braking system, but that again raises the question that perhaps Kubota puts lower quality brakes on their tractors because they do NOT recommend wheel weights and NH puts higher quality brakes on their tractors because they DO allow wheel weights? And in both cases, adding ANY weight to the tractor will increase the workload of the brake system anyway.

Personally, I think it is capitalism. I think Kubota knows that people will fill the tires or put on EZ Weights and Kubota won't make a profit on that. However, Kubota will make a profit by selling you their suitcase weights.

 

[Bob_Skurka]

Re: Wheel VS Frame weighs...what\'s up?

By the way, my OLD and SMALL Cub Cadet garden tractor (which has a hydrostatic tranny) has 150 pound wheel weights on the rears. They are factory weights with the Cub Cadet logo molded into the side of them.


At 75# per wheel, I have to assume that the engine torque and the braking capabilities of that little Cub garden tractor are far stouter than the the Kubota B2910 because I am not supposed to weight its rears????



I will stick with my arguement about CAPITALISM and Kubota wanting to make money on the sale of weights. Somehow I seriously doubt that my little Cub is as sturdy as a big Kubota.

 

[Henro]

Re: Wheel VS Frame weighs...what\'s up?

Bob pretty much sums up my thought process...

Aside from the fact that we are talking VERY low RPM, if we consider wheel weights, they are quite close to the center of the mass of the tire, so they would not add as much energy to the rotating mass as weight on the outside of the tire would...like might be considered when foam filling tires...

Another thought. Liquid in the tires may not add much strain to the tractor on start, because it would not be forced to rotate like foam filling would. The surface of the tire would initially slip past the liquid filling, and the liquid would only gradually get up to rotating with the tire, if the tire moved fast enough for this to happen.

It is possible that at very low speed the liquid in the tractor tire does not even rotate at all! Well I guess that would be a function of how full the tire was...but you can see my point, probably...I hope... /forums/images/graemlins/blush.gif

Let's say the tractor is on a hill. Beside an identical tractor that has frame weights rather than filled tires. The tractor that has filled tires has them filled with liquid. Gross weight is the same for both.

When the liquid filled tire tractor starts moving, the it seems to me the engine and drive train have to work just about exactly the same as the other tractor. The friction at the interface between the wheel/tire and the liquid in the tire would add a slight amount to the equationwould be essentially just sitting in place, while the tire moved around it.

Take you coffee cut and drop a crumb from your toast in it. Then grab the handle and rotate the cup while watching the crumb...the handle will move a lot and the crumb will not move much [or at all depending how good you are]. The liquid in the tire is the coffee; the cup is the tire...

A tire filled with solid foam, would be different, but would that be enough to worry about? I would say yes it would on a quarter mile sprint car...but can't see how it would matter much on a tractor...the wheels just turn too slow, at least most of the time [maybe even all of the time, where is that old physics textbook when you need it ???] /forums/images/graemlins/smile.gif

Now take that doughnut and put in on your finger... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif Just joking... /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif

 

[zuiko]

Re: Wheel VS Frame weighs...what\'s up?

The only valid reason I can think of is if you are using weight to counteract a load on the front or back of the tractor, the further out it is the more effective it is. So if you want to carry around a FEL full of rocks or a heavy implement you would need more wheel weights to do the same job. Then you would end up with more weight on the axels.

The lower CG is a big argument in favor of wheel weights (esp loaded tires) though IMO.