B2150hst 4WD Tire Help - Lead/Lag Mechanical Ratio

[B2150hsd]

Have been looking into replacing rear tires and learning about the importance of Rolling Circumference on a tractors 4wd. To confirm that the tractors current front and rear tires have the correct RC to match the Mechanical Ratio for Lead and Lag, I marked a front and rear tire then drove in 2wd on hard pavement for one full tire rotation. The result was when the front tire turned once, the rear tire was lagging by a lot. The rear tire mark was at about the 2 o'clock position. One interesting thing is when taking the tractor out of 4wd it never feels likes it binding. The lever moves smoothly out of 4wd.

The rear tire is the original 12.4-16 Firestone R1. The front is a Carlisle 6x12 R1. The original front was a Bridgestone that is no longer available. I have spent many hours trying to find what the front tire should be and what the Mechanical Ratio is. I tried Kubota Corporate and they said to work with a dealer. I spoke with a dealer and they had no idea what I was talking about and said to call Corporate. I have also read many threads on multiple forums but can not get a clear answer on what is the correct front tire dimensions.

The front Carlisle tire is 23 inches tall with a RC of 68.9. According to Firestones current specs the rear tire 37.6 inches tall with an RC of 106. However, the tire on the tractor is 30 years old and I have no idea if the dimensions have changed. The tractor only has 650 hours and all on grass so the lugs look great with minimum loss of tire circumference.

I did find a sheet from another forum thread that posted the Mechanical Ratio for a B8200. The B8200 uses the same tires as the B2150 so one would think the mechanical ratio would be the same. When I calculate the lead/lag with my current tires using the B8200 mechanical ratio of 1.691 it calculates a lead of 9.9%.


Lead Lag Calculator

Anyone know what front tire(s) are correct? And the Mechanical Ratio?

 

[diesel85]

4wd is meant for soft surfaces that allow give. Such surfaces are: Wet grass, loose dirt/mud, snow, ice, and sand.

Never run in 4wd on pavement or concrete.

It not only eats tires but binds up the drive train.

If the machine is heavy enough, it can actually tear up fresh or hot asphalt pavement when turning as it binds. Or leave tire marks in pavement.

I only run 4wd sparingly during the summer. During the winter, because there is always snow and ice, it will stay on 90% of the time, UNLESS I'm on dry pavement, such as a cleared road.

 

[B2150hsd]

Yes, thank you. I have owned many 4wd vehicles and am aware hence this post about incorrect tire sizes creating mismatched front and rear ratios. Used to belong to the Lake Tahoe Hi Lo Jeep Club and spent weekends in the Rubicon Jeep Trail. Took a 1951 Willys M38 and put a chevy v6, a school bus 4 speed trans with compound low, added an over drive, power steering... good times.


Let me add that the difference in tractor Lead should be 0-3% or 0-5% depending on what you read. The tractor front should never Lag.

 

[gator]

According to the Workshop manual (WSM) available at this link: HERE. The following pdf from the WSM for tires shows you have the correct sizes (yellow highlight):View attachment Untitled.pdf
EDIT: The 2150 HST 4WD tire size on pdf page 9 is missing the front and rear label but is the same size as the attached pdf.

 

[Dave M7040]

You are being prudent in selecting tires.

You will learn that many brands of tires from outside North America fail to follow the tire "Bible," the Tire and Rim Association Hand Book.

I have seen a MITAS tire on a new M7040 be 3" smaller in diameter than the TRA handbook spec. That creates a circumference that is over 9" too small.

Look over the attached material and note that the diameter of tires changes as the tires age or "Grow."
Also, the diameter changes for the same size, say 16.9 x 28, depending upon R1, R2 and R3 &4

Radials have their own set of diameters.

Rely on the published literature by companies like Firestone and do your best to create the front to rear ratio which has been working well for you over years.

Dave M7040

 

[rScotty]

I've written on this subject before and so have others. Here are some tricks:

1. It is not too difficult to determine your tractor's internal gear ratio, but it is usually available in the specs in the shop manual....
2. You can mark the front & rear tire with a paint blob and drive on a flat straight road in 2wd. Then measure the average distance between paint spots and that will give the real front to rear tire ratio.
3. When using tire mfg specs to mathematically calculate ratios you cannot use diameter or circumference; you should use "loaded rolling circumference, sometimes just called "rolling circumference".
4. Most internal ratios are designed around a specific tire recommendation so that front tires travel from 3 to 5% farther than the rears. The front tires are therefore always pulling the tractor; that maintains steering control.
5. Surprisingly, many tractors do not have a positive latch on the 2wd/4wd selection lever. Sometimes it's just a loose lever that slides a splined collar back and forth. Those depend on a bit of driveshaft windup to keep it in 4wd, and the 5% ratio inbalance to keep it in 2WD.
6. Even more surprisingly, #5 method works pretty well as long as the internal vs tire ratio is far enough away from 1:1. But if it yours is self-shifting, just put some sort of hold down on the 2wd/4wd selector lever.
7. Most tractors are 4wd assist; they are not designed to be full time 4WD. So don't use 4wd unless the surface allows for some tire slippage. Especially not in 4wd on pavement with a full FEL bucket or when turning.
good ratios to you,
rScotty

 

[B2150hsd]

I have the WSM and no mention of Mechanical Ratio, Lead Lag.

Has anyone actually tried rScotty #2 suggestion? The accuracy of a paint blob and the amount of paint left on the driveway will be interesting. And the paint blob will need to be placed on the bottom of each tire at the same spot relative to each other? The B8200 Mechanical Ratio Kubota provided, attached in first post, is 1.691.

Their must be at least one B2150 4wd owner with AG tires that knows what tire actually works.

 

[rScotty]

I have the WSM and no mention of Mechanical Ratio, Lead Lag.

Has anyone actually tried rScotty #2 suggestion? The accuracy of a paint blob and the amount of paint left on the driveway will be interesting. And the paint blob will need to be placed on the bottom of each tire at the same spot relative to each other? The B8200 Mechanical Ratio Kubota provided, attached in first post, is 1.691.

Their must be at least one B2150 4wd owner with AG tires that knows what tire actually works.

Let me help here. I've done this many times. In fact, I could post pages from my notebooks.

The paint blob test is handy because It is much easier to get the internal mechanical ratio of the tractor than it is to determine a similar ratio for the tires. The paint blob test gives you the tire ratio

No, the paint blobs will not need to be placed at the bottom of each tire relative to each other in any way. In fact, just do it one tire at a time, and do the arithmetic later.

What you are measuring is the distance between paint blobs ....and what you are determining is the "loaded circumference" of the tire.
BTW, a driveway may not be long enough..... and anyway who wants paint on a driveway? I use a convenient paved road. You want a flat straight surface about 30 to 50 yards long.....enough for maybe 10 rotations of the tire. I do one front tire first. Put a blob of thick white paint the size of a quarter on the top of the tire and drive for maybe 20 yeards. Then measure the average distance between paint marks.

Next, do the same with the same side rear tire. Drive the same course, but you will have to drive farther. Measure and average.

For both tires, the average is necessary because you are going to be surprised at how much the distance varies from one blob to the next. I think this is due to slight differences in how straight you go.

The paint blob test won't give you the mechanical ratio; it gives you measurements for the real rolling circumference of the tires....from which you can form a ratio showing how for one tire travels relative to the other. That gives you a ratio we can call the 2wd ratio.

Once you have that front to rear tire ratio, you then compare it to the internal mechanical ratio (which I call the 4wd ratio) of the tractor gearing to see how the tire ratio compares to the internal gear ratio. The ratios should be close, and should show that in 4wd the front tires are trying to travel farther than the rears when 4wd is engaged.
good luck,
rScotty

 

[art]

Stick with the same size tires you have. We often have to balance with tire pressures to balance out the drive train. Run the fronts high but not over the maximum for loader use and then adjust the rears which typically is about ten to 12 lbs.

 

[rScotty]

You are being prudent in selecting tires.

You will learn that many brands of tires from outside North America fail to follow the tire "Bible," the Tire and Rim Association Hand Book.

I have seen a MITAS tire on a new M7040 be 3" smaller in diameter than the TRA handbook spec. That creates a circumference that is over 9" too small.

Look over the attached material and note that the diameter of tires changes as the tires age or "Grow."
Also, the diameter changes for the same size, say 16.9 x 28, depending upon R1, R2 and R3 &4

Radials have their own set of diameters.

Rely on the published literature by companies like Firestone and do your best to create the front to rear ratio which has been working well for you over years.

Dave M7040

Dave, that's where I started with charts like that years ago. And what I found out is that none of those measurements are what you are looking for to calculate lead vs lag or front to rear ratio.
Those are arithmatic diameters for a theoretically round tire. That works for circular things, but not for tires because they aren't round when they are on the tractor.
What you want is a spec that is called the "loaded circumference". That is the spec used for the gearing calculations, and all tire companies have it available although sometimes you will have to go to the engineering specs to find it. As you might suspect, it is dependent on load, flexibility, and psi.

The difference between calculated circular circumference and actual loaded circumference will typically be large enough of a difference to completely mask what you are trying to accomplish - which is to make the front tires turn about 5% faster than the rears when in 4wd.
rScotty