Front tires caused axle failure...?

[rScotty]

No I meant the loaded radius, the loaded circumference can be calculated from the loaded radius. The loaded radius is easier to measure with a stationary tractor.
The loaded radius is affected by load and tire pressure which in turn affects the loaded rolling circumference.
The taller the sidewall of a tire the more loading and pressure can effect those values.
When you get into taller tires it can easily be seen how inflation affects loaded radius or loaded rolling circumference,
You can reduce or increase the lead lag ratio by varying tire pressure, with a radial 30" or larger tire the loaded radius can change by a half an inch.

How would you go about calculating the rolling circumference from a loaded radius? I'm willing to believe that it can be done, and the more I think about it the more I would like to learn more about it.

First things first.... I am using the term "loaded radius" to be the vertical distance from the center point of the axle to the surface of the ground. That distance is basically ground clearance. It will vary with load as the tire squats, but will remain constant as long as the load doesn't change. And part of the tire is flat against the ground.

So a bug crawling around the circumference of that tire would be traveling in an ellipse with one flat area. The distance he crawls around that ellipse plus the length of the flat area against the ground is the "rolling circumference".

I'm naturally lazy, and have never really got down and worked out a formula complex enough to solve the relationship between a changing radius and the resulting circumference. You see that sort of thing in orbital math where the distance an object moves in a path can be calculated in spite of the fact that the path is elliptical. So the path of an ellipse is a solvable relationship, especially if we ignore the flat spot where it meets the ground and the fact that the ellipse changes with load and pressure.... although it's getting ugly....

To keep things simple, I'd probably do what the manufacturers do and say that the formula only works for one specific tire at one pressure. That's how they give both static loaded radius and dynamic rolling circumference in their specs. So there's a relationship, but it sure isn't pi. My bet is it is just an average relationship that only works for their tires over a small range of loads and pressures.

Of course there is a simpler way. You can always measure to create specs. It may be that manufacturers measure both rolling circumference and loaded radius instead of trying to calculate one from the other. That's what I do. Then there's no need for some exotic formula. Measuring is easy to do and always right.
rScotty

 

[Oldpath05]

Loaded or unloaded radius makes very little difference, the only way that become an issue is if one put 100pis in rears and 10psi in front. Right tire size is what to go by, the OP didn't put right tire size on front of the tractor, you cant change front without changing rear to factory specs. That's why when the dealer told me I could go with R4 or turf tires I'd have to change front and rear at the same time, width is also is a none issue unless you double up the fronts, it is and always be radius in on tires. that's my point and I'm sticking to it, everything else is fake news...........

 

[LouNY]

It is the same basic formula as for any circle;
C=2*PI*r or C=2r(pi) with Pi being roughly 3.14
So if the exact centerline of a tire and rim combination can be found and measured to the ground or floor.
A 20.8R-42 can have a static rolling radius of 34.5" and a stated Rolling Circumference of 228 Inches.
You can vary that considerably with just a 5-10# air pressure change.
But ; 2*{pi}3.14 * 34.5" = 216.66"
the same as 2*34.5"*3.14= 216.66"
And yes you certainly can just measure to get the rolling circumference, mark the tire and ground and roll it exactly one revolution and mark and measure the distance on the ground.

 

[LouNY]

Loaded or unloaded radius makes very little difference, the only way that become an issue is if one put 100pis in rears and 10psi in front. Right tire size is what to go by, the OP didn't put right tire size on front of the tractor, you cant change front without changing rear to factory specs. That's why when the dealer told me I could go with R4 or turf tires I'd have to change front and rear at the same time, width is also is a none issue unless you double up the fronts, it is and always be radius in on tires. that's my point and I'm sticking to it, everything else is fake news...........

Well it's a good thing that we can agree to disagree.
It is amazing the difference in radius or circumference between different tires of the same size and type but different manufacture and models.
One of the tractors on the farm had such a mismatch of tires from the factory that it would lurch tremendously engaging or disengaging 4wd,
They went through several sets and brands of tires to get an acceptable set all of the same sizes per the sidewalls.

 

[Oldpath05]

:thumbsup:I love agreeing to disagree, makes a great discussion that most cant appreciate, but yeah same brand sometimes make a difference to......

 

[the old grind]

I suspect the PO likely drove those gears to near death in FWA mode (>3khrs is plenty) and suggest that s__ falling apart was as coincidental to the tire replacement as causal.

 

[thoner7]

Does anyone know the bolt pattern for the front wheels? I just measured 6 1/8 6 lug with a 4 5/8 center hole. .maybe I was a tad off but that's quite close to a typical 6 lug 4 1/2 center hole which is quite common.

I assume they are a metric size being a Japanese tractor?

 

[Oldpath05]

Gee wiz that to me is a strange question, the bolt pattern is already there on the wheel and hub.

 

[thoner7]

Gee wiz that to me is a strange question, the bolt pattern is already there on the wheel and hub.

Thanks for your well thought out advice.

 

[Smokeydog]

Wonder how many times the front axle oil was changed? FEL and 4wd work requires maintenance.