Tires A physics question of leverage

[ovrszd]

I run spacers on my Yamaha Rhino, Kubota RTV and Jeep Offroad Buggy. I've never had a failure. My biggest concern is making sure the bolts holding the spacer to the vehicle axle are tight and never loosen.

I don't think you will see a failure with your setup.

 

[AxleHub]

Lenny,

I'm talking about the combination effect.

1. Axle bearings and lugs andvaxles are designed for a certain max weight load on a vertical support. But when you change your rim distance you change vertical to vertical leveraged. Then you add sidehill and its angle vertical leveraged and that is all factored in to engineering. But now if you add spacers there is a lug extension now involved and lets say thats 3 irb4 inches on each side of ADDED leverage impact ro consider in.

2. Think of it another way . . A floor joist is 2 x 10 rated for a 10 foot span. But if youbgo to a 12 foot span a 2 x 10 is no longer good because youve changed the engineering in a leveraged method . . Not an additive method. Adfing 3 or 4 inches of spacer on each side AFTER extending the rums too on sidehills is not additive its multiplied because bearings are verticle not angled vetticle just as lug combinations are.

I can't say what your teactor load can endure on a sidehill with weight with multiple leveraged extenstions if the width. My point is . . I'd ask someone really smart in engineering of your teactor before I'd be doing bith spacers if lobger suze AND extending the rims too.

Jmho

 

[lennyzx11]

Lenny,

I'm talking about the combination effect.

1. Axle bearings and lugs andvaxles are designed for a certain max weight load on a vertical support. But when you change your rim distance you change vertical to vertical leveraged. Then you add sidehill and its angle vertical leveraged and that is all factored in to engineering. But now if you add spacers there is a lug extension now involved and lets say thats 3 irb4 inches on each side of ADDED leverage impact ro consider in.

2. Think of it another way . . A floor joist is 2 x 10 rated for a 10 foot span. But if youbgo to a 12 foot span a 2 x 10 is no longer good because youve changed the engineering in a leveraged method . . Not an additive method. Adfing 3 or 4 inches of spacer on each side AFTER extending the rums too on sidehills is not additive its multiplied because bearings are verticle not angled vetticle just as lug combinations are.

I can't say what your teactor load can endure on a sidehill with weight with multiple leveraged extenstions if the width. My point is . . I'd ask someone really smart in engineering of your teactor before I'd be doing bith spacers if lobger suze AND extending the rims too.

Jmho

Good point taken, Axlehub!

As I said this was mostly for a round table discussion for varied opinions. I'll still do it. I'm not pulling a plow or working mine for a living like some of you guys.
The actual physics/science was what I was interested in and I have seen some very detailed smart answers come off this board regarding a multitude of subjects.

 

[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.

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

OP has posed the question on the condition of the tire contact width the same, but attached to the axle in a dished in or dished out mode. [Appropriate spacers would be used to accomplish this for the dished in mode.] The two setups posited result in cantilever forces on the axle or the spacer extended axle. The cantilever is out on the dished out "narrow axle" setup, but exactly the same amount in on the dished in setup mount on the wider [spacer extended] axle.

The axle/bearings/etc wont see any difference. Stability will be statically identical, but dynamically it will be minutely more, or less, with the dished in setup when encountering sidehill hollows on the lowside, or bumps on the highside, respectively. -- This is an inertial effect; due to the heavier part of the dished in hub being further out ... A verrry small issue. -- Also small is the mass of the spacers wrt tractor causing more stability by a minuscule lowering of the tractor center of mass.

 

[dickfoster]

Ok. Stop reading now unless you have time to waste.
I warned you.

My Kubota with AG tires had adjustable rims.
There is about 3-4" of adjustment in the rims.
I just bought wheel spacers that are 3".

Just on the science theory, which way would make the tractor more stable on a side hill?
Say the outer part of the tires touching the ground is 65" as a baseline with both settings.
With the "rim" sticking out past the end of axle or the end of the axle/spacer sticking out past the "centerline" of the tire vertically,
Causing a bit of cantilever. Which would be more stable in respect to the center of gravity overturning the tractor on a side slope.

Yes I know. Both is better.
Inquiring minds want to know. I know some of you will ponder this. **** OCD!

As long as you're talking physics and spacers, you'd do well to consider what effects that added leverage has on your axles and wheel bearings. For starters the wheel bearings simply aren't designed to be loaded cockeyed like that, they want direct compression loads. For the effect on the axle, pinch a pencil between your fingers in the middle and wiggle one end up and down, then pinch the pencil at one end and do the same. That's leverage working against you.

When I asked my dealer about spacers and the effect on warranty, spacers came out on the short end of the stick.

 

[SPYDERLK]

Ok. Stop reading now unless you have time to waste.
I warned you.

My Kubota with AG tires had adjustable rims.
There is about 3-4" of adjustment in the rims.
I just bought wheel spacers that are 3".

Just on the science theory, which way would make the tractor more stable on a side hill?
Say the outer part of the tires touching the ground is 65" as a baseline with both settings.
With the "rim" sticking out past the end of axle or the end of the axle/spacer sticking out past the "centerline" of the tire vertically,
Causing a bit of cantilever. Which would be more stable in respect to the center of gravity overturning the tractor on a side slope.

Yes I know. Both is better.
Inquiring minds want to know. I know some of you will ponder this. **** OCD!

As long as you're talking physics and spacers, you'd do well to consider what effects that added leverage has on your axles and wheel bearings. For starters the wheel bearings simply aren't designed to be loaded cockeyed like that, they want direct compression loads. For the effect on the axle, pinch a pencil between your fingers in the middle and wiggle one end up and down, then pinch the pencil at one end and do the same. That's leverage working against you.

When I asked my dealer about spacers and the effect on warranty, spacers came out on the short end of the stick.

You included the OP but did you read it? The original design provides adjustment and presumably design margin to allow for the greater stresses. Beyond the the OEM adjustment width is where one would assume responsibility to be prudent.

 

[dieselcrawler]

I made spacers to fit between the center dish, and the outter rim. The added load from the additional leverage was factored into my decision to do so, my thinking that the wear on bearing was cheaper to repair than damage to my head if I rolled on my steep hillsides. I've also built a full cage ROPS.





I realize this has gone beyond the original of one vs the other, but...

 

[N2DFire]

due to the heavier part of the dished in hub being further out ... A verrry small issue

Ok - I think the crux of our disagreement is this statement in conjunction with your previous use of the word "equivalent"

As I said before in real world application the difference would be insignificant, but mathematically (in theory - likewise where the OP stated) there IS a difference.

2.01 is not equivalent to 2 (even for very large values of 2) however the difference may be insignificant depending on the situation at hand.

In essence we are arguing semantics and accuracy instead of physics so why argue?

(And yes my example was very much an over simplification intended to demonstrate the effects in question and I realize that changing the width between your fingers was outside the parameters of the question aka "cheating").

 

[lennyzx11]

As long <CUT .

SNIP>When I asked my dealer about spacers and the effect on warranty, spacers came out on the short end of the stick.

yet they(Kubota) sell a 2" spacer to facilitate the use of tire chains. And I don't see in the manual Not to. On the front yes but nothing in ref the rear.

Ok we can wind this up. I was wanting the physics/math and I've gotten some very intelligent answers to think upon.
Thanks all,
Lenny

 

[AxleHub]

Ok - I think the crux of our disagreement is this statement in conjunction with your previous use of the word "equivalent"

As I said before in real world application the difference would be insignificant, but mathematically (in theory - likewise where the OP stated) there IS a difference.

2.01 is not equivalent to 2 (even for very large values of 2) however the difference may be insignificant depending on the situation at hand.

In essence we are arguing semantics and accuracy instead of physics so why argue?

(And yes my example was very much an over simplification intended to demonstrate the effects in question and I realize that changing the width between your fingers was outside the parameters of the question aka "cheating").

There are two different stories goin on in this thread:

Story 1. Is comparing impacts of adjusting rims to increase width of rear wheels stance VS. Using spacers. Story 1 was not contested to speak of becayse itvwas virtually the same impact.

Story 2. Is not story 1. Story 2 quickly developed because some said to do both instead of 1 or the other. That's when instarted posting more about bearings and lugs and side pressure and that doing both things was far different because a user would be leveraging (multiplying) the negative concerns and not just adding them.


When you start changing width by 3 or 4 inches on each side . . that may have been engineered into specs.. But when you change rims 3 or 4 inches on each side AND YOU ADD 3 or 4 inch spacers . . You've made a huge alteration in design . . especially on sidehill issues.

.