JD wheele on a Mahindra

[Fallon]

If I recall Kubotas front tires run about 5% faster than the rears. So the ratio doesn't need to be perfect. They do that intentionally for improved steering performance. The slightly faster fronts will pull the tractor where they are pointed mitigating the better traction of the rears trying to keep things straight, more or less. Of course with some sacrifice for tire life.

 

[Spentit]

That is a good sign. Makes sense as well. Thanks

 

[Villengineer]

I've put Kubota rims on a JD before and you might find this thread helpful:
http://www.tractorbynet.com/forums/build-yourself/120848-redoing-wheels-wrong-bolt-pattern.html
As mentioned before, both the bolt pattern and center hole are important. I had to alter both to get the Kubota rims to fit. You need to get the tire ratios as close as possible. It's been a while, but I seem to remember that you need the rolling circumference for the specific tire. I don't think you can rely on the size designation.

 

[rScotty]

Here are the numbers... Donor tires circumference : front 91", rear 153". Tires being replaced: front 109", rear 160". The question would be are the ratios's per revolution close. I can't do the math.....Anyone?

OK, I've done that very thing a number of times.
The really good way to compare ratios is not the manufacturer's specified circumference, but instead using a number called "loaded rolling circumference". It's an easy number to get and no math involved.
We know that the front to rear tire ratio on the Mahindra is correct to match the internal tractor's Front to Rear transmission ratio right because those tires you have on it now are the factory originals and they are working for you. (I hope)

There are two ways to get the loaded rolling circumference. If you know the tractor's weight and pressure in the tire you can call the manufacturer of that tire and get to their technical department. They know the rolling circumference of their own tires, and they know why you need to know it.

Or there's an easier way that you KNOW is right. Here's how:

Pick a nice day, take a can of thick house paint of some color, a long tape measure, pencil and notebook, and find yourself a stretch of straight dry concrete or asphalt roadway a few hundred feet long.
Put a blob of sticky wet paint on one of the rear tire treads on one side and do the same for one front tire on the other side.
Hop on and just drive slowly in a dead straight line down the road.
Get down and measure the average distance between the blobs of paint left by each tire. You may have to do this several times to get good paint splotchs left on the road.

The distance traveled between any two blobs of paint is the loaded rolling circumference of that tire. The measurement will probably vary, so measure half a dozen to get an average. Don't be too surprised to find that your average loaded rolling circumference is a little different from the manufacturer's listed circumference for that tire. That's ok because what you have now is the real number for your tractor. Save those notes.

You can find the tire ratio by dividing the average distance between front wheel blobs by the average distance between rear wheel blobs. That gives you a decimal that is less than one - which is handy because if you multiply that number by 100 it becomes the front to rear percentage ratio.

Now all you need to do is to find replacement tires with the same ratio or close. Try to stay within 5% or your original measured ratio.
good luck,
rScotty

 

[rScotty]

Here are the numbers... Donor tires circumference : front 91", rear 153". Tires being replaced: front 109", rear 160". The question would be are the ratios's per revolution close. I can't do the math.....Anyone?

I just wrote on how to find the circumference number that you really want - the Loaded Rolling Circumference. I urge you to get that number. It can save expensive repairs and makes it easier to compare donor tires.

But if for some reason you can't do that, you can at least find out if the tires you are considering are anywhere close. We can do that as an example with the numbers you have posted:

Your tractor's tires now are 109" front and 160" rear. We divide the two numbers to get a front to rear ratio of 109/160 = .68 . Or you can divide Rear/Front and get 1.46.
The way I did it first, allows you to multiply by 100 by shifting the decimal place two places to the right and calling it a F/R percentage ratio of 68%.

The Donor tires are front 91 and rear 153. F/R is 91/153 = .59 or 59%. ( or you could divide Rear/Front and get 1.68.)

You are off by 10%, and that's a bit too much for the drivetrain. It is also going to be a ***** to shift out of 4wd on any high traction surface. Also I can see by those numbers that we are going in the wrong direction...with those donors it is going to end up being hard to steer and will plow the front end when turning. Darn.... but read on....

Because that's not the end of the story. When you do the paint blob measurement to get the real loaded rolling circumference it may come out closer. And that will tell us the real story.
rScotty

 

[Dave M7040]

Take this issue of correctly replicating the front to rear ratios very seriously. The mechanical damage that is possible will be very expensive.
It will happen that you forget to come out of 4WD before moving unto a hard surface.
If you are concerned with lawn damage, the mis-match from factory ratios will be tearing up your lawn.

A number of years ago companies like John Deere put a label on the seat back of their 4 WD tractors as it was such an important number.
The WSM manuals had this info

Dave M7040

 

[electrycmonk]

D-a-n-g...... 4+ hrs later; many threads read; several threads saved; a few replied in; and finally - just after midnight I find the equation and the real world data in one thread & clearly explained too. Okay. Now I'm done for the night.
/Subscribed

 

[rScotty]

D-a-n-g...... 4+ hrs later; many threads read; several threads saved; a few replied in; and finally - just after midnight I find the equation and the real world data in one thread & clearly explained too. Okay. Now I'm done for the night.
/Subscribed

Concrats on being so determined, and thanks for posting that JD sticker. That's handy to have.

Reading through the sticker, I was glad they pointed out the importance of using "rolling circumference".
When looking up that info on a tire manufacturer's tech site, it may be called: "Loaded Rolling Circumference... same thing. They just put the "Loaded" into the dimension because tire shape & circumference changes significantly with tractor weight.

You may not be able to find rolling circumference on the tire manufacturer's site. Not all of them list it. And RC is one really tough value to calculate, but the good news is that anyone can measure it. In fact, anyone can measure it very accurately for their own specific tractor weight and used tire circumference. One way to do so is in message #14 above. I should add that RC measurement method in post #14 should be done in 2wd, NOT in 4wd.

JD's sticker points out that the other piece of information needed is the the front and rear internal axle ring/pinion gear ratios. Apparently JD posts those values on the tractor itself, but that's rarely true for other makes. Luckily, gear ratios are also something that can be measured on your own tractor.

Enjoy!
rScotty