Tires A physics question of leverage

[lennyzx11]

Yes. I know that using both is the best. The thought was only a provoking one over multiple beers last night. I was looking for something like N2DFire posted.

Only for fun(and learning).

I plan on using both methods at same time.

Never thought about that with Turf tires being better on side slope. But I understand it now.

This was just idle musing. Thanks for the answers! Out on the road working and having tractor withdrawals.

 

[JRobyn]

Trying (with not much success) to think back on my Mechanics courses at GaTech. So with the outer edge of the rims at 65" width either way, the difference will be where the wheel center disks are. Thus, I think that the main difference will be in the amount of bending (beam) stress that is on the axle. And different stresses in the wheel center disk as they are transferred from ground to tractor.

 

[flusher]

Set the wheel track was wide as possible and get the center of gravity as low as possible for maximum stability on slopes.

Here's a few photos of my 1964 MF135 diesel that's been modified to squat real low for mowing and discing work in the orchard. The rears are 18.6 x 16 tires mounted on 16 inch diameter rims and are filled about 2/3 with fluid (water since there's no freezing hazard in the North Sacramento Valley). The front axle spindles have been shortened to keep the tractor level. The track width measures 84 inches to the outside walls of the tires and the rear axle centerline is about 18" above ground.



It helps if your tractor is a straddle type (seat bottom is on top of the transmission with your lower legs straddling the transmission case). Helps keep the CG low.

 

[AxleHub]

Yes. I know that using both is the best. The thought was only a provoking one over multiple beers last night. I was looking for something like N2DFire posted.

Only for fun(and learning).

I plan on using both methods at same time.

Never thought about that with Turf tires being better on side slope. But I understand it now.

This was just idle musing. Thanks for the answers! Out on the road working and having tractor withdrawals.

Actually, you may want to get an adfitional opinion before using both methods at the samevtime.

1. Adjustable rims are engineered to offer axle strength and lug support at the minor or major settings. Both the lugs and axle are calculatedvwith stress loads at maximum settings and weights.

Similsrly spacers are designed to extend support based axle and lug extension.

However neither is engineered to alter the geometry by the amount you are describing . . Yes either one . . But not both. Compound that with the desire for side hill use and the geometry creates much larger leveragedangular tensile stresses. You're putting lug extensions on to extended lugs and then stresding them at their maximum extension besides . . That creates considerable angular stresses that are unlike veryical stresses. And then you also have axle and bearing stresses at extended angular presdures as well.

My point is . . your axle may be overbuilt enough to acvomodate both spacer and extension . . but are the lugs and bearings capable with both those conditions and sidehill stresses included?

 

[SPYDERLK]

ok - let me see if I have this

Thinking of the Wheel / Rim as a Dish (or cereal bowl) shape and assuming that no matter which way to turn the "dish" both setup's result in the same 65" edge to edge wheel track, you're asking which way would be more stable Dish "Out" (big end to outside) or Dish "In" (big end toward Tractor).

With Dish Out - all (or nearly all) of the longitudinal mass will be between the vertical center-lines of the tires.
With Dish In - a small portion of the longitudinal mass will be on the outside of the vertical center-lines of the tires.

So - in theory - the outside mass of the Dish In position on the low side wheel would act as a counter weight to the (much larger) remaining mass inside the wheel (when you think of the center line of the wheel as the pivot point / fulcrum). In simple terms - any weight placed on the outside of the center line of the down hill wheel will act in opposition to the mass on the inside of the center line.

This would not necessarily move the CG any higher but would move it slightly closer to the down hill wheel.

So - to answer your question - Dish Out would be more stable but the difference would be insignificant in real world application.

If you are really bored and want to have some fun with physics - take a ruler and hang (equal) weights at the very ends, then move your fingers about 2" inside on each end and see how much effort it takes to lift one end (tip the tractor) - this is Dish In

Next swap the weights to the 2" inboard position and your fingers to the outside edges and try to tip it again - this is Dish Out.

Incorrect. The conditions on the tractor are equivalent to one another. They are not equivalent to the entirely different setup of your ruler comparison.

 

[N2DFire]

Incorrect. The conditions on the tractor are equivalent to one another. They are not equivalent to the entirely different setup of your ruler comparison.

Please elaborate on how these two conditions on the tractor are equivalent.

 

[ovrszd]

You guys are way over my head. I'm still struggling with turf versus industrial or AG. Around here anyone mowing steep banks run R4 or R1. Even on Zero Turn mowers.

 

[brown40]

Technically speaking, the spacer adds mass at the hub, and weight to the equation, so you have negligibly more psi using extra gear. The extra 6" dished out with the spacers should make for a stable and more aggressive looking machine. You'll have to do some before & after pics for those considering spacers, or on the fence about dishing out their tires.

 

[ovrszd]

On my 3 tractors, 2 have adjustable wheels, 1 has reversible wheels. I run them as wide as I can with the attachments that I use. If I had wider attachments, I'd run my wheels wider. I never thought much about the configuration of the centers/rims of the adjustable ones. I'm not sure that measurement is negligible in real life. Mathematically, probly. :confused3:

 

[lennyzx11]

Actually, you may want to get an adfitional opinion before using both methods at the samevtime.

1. Adjustable rims are engineered to offer axle strength and lug support at the minor or major settings. Both the lugs and axle are calculatedvwith stress loads at maximum settings and weights.

Similsrly spacers are designed to extend support based axle and lug extension.

However neither is engineered to alter the geometry by the amount you are describing . . Yes either one . . But not both. Compound that with the desire for side hill use and the geometry creates much larger leveragedangular tensile stresses. You're putting lug extensions on to extended lugs and then stresding them at their maximum extension besides . . That creates considerable angular stresses that are unlike veryical stresses. And then you also have axle and bearing stresses at extended angular presdures as well.

My point is . . your axle may be overbuilt enough to acvomodate both spacer and extension . . but are the lugs and bearings capable with both those conditions and sidehill stresses included?

I don't think I am putting lug extensions onto extended lugs as you say here. I AM putting the spacer in as normal. I've "read it on the Internet" that Kubota themselves sells a 2" spacer for this tractor. There is more stress I absolutely agree. But not quite as much leverage as you describe. (I think)
Here's a pic of how my wheels adjust. They are filled BTW.


With the lighter weight of a smaller tractor like this and it's capabilities of picking up most of its own weight with the FEL or 3pt, I feel that the bearings are engineered to handle that weight and would be more than capable of handling any force that a person could put on a downhill wheel during side slope operations.

Kinda like even taking a D9 Dozer or winch and pushing/pulling the tractor sideways would not snap that axle or bearing. The tractor would slip away or flip over if an obstruction was encountered.

To me, it seems like the tractor would slip or tip before that much destructive force could ever be placed on that bearing.
I have been following and researching on wheel bearing failures also and have yet to find a case of a tractor wheel bearing failing because of running spacers. Some even at 6-10 inches right here on this board. Big tractors, carrying a lot of weight and working hard.

Or do you guys think that axle and bearing is weaker than I'm giving it credit for?