JD750 4WD Tire Size question

[ctandc]

Original Bridgestone R3 6-14 tires, one of them at least finally bit the dust. Holes in the sidewall, tube blew - thought someone was shooting at me. LOL.
They are really proud of those Bridgestones, when you can find them.

Diameter is right at 25". Wondering if throwing on some 25x8.5x14s would work? Would they mount on the 6" rim?

Tire ratio for 4WD appears to be okay, just adding a bit of width.

If not - any issues going to the

6-14 REGENCY AG COMPACT TRACTOR TIRE 4 PLY​

They are R1, not turf, and eventually I'll go to R1 in the rear anyway.

 

[LouNY]

If the diameter or loaded radius is similar should be fine, when I looked up the 6-14 it listed a 24 inch diameter.

 

[rScotty]

If the diameter or loaded radius is similar should be fine, when I looked up the 6-14 it listed a 24 inch diameter.

I think Lou means loaded diameter, not radius.
But I'm curious why not replace them with the same tire again? Tire price is nothing compared to the expense that can happen with a 4wd and mismatched tires.

 

[pmsmechanic]

I installed 26x12x12's on my 4410 in place of the factory 25x8.5 x14 tires. In 3000 hours the only issues I've had is wrecked tires from to low a ply rating. Going to 6 ply tires solved that. The tires are slightly larger but the only issue is that the front doesn't lead as much, which results in the front tires skidding on sharp corners. If it bothers me I just disengage the front wheels for corners. All in all the benefits outweigh the disadvantages.

 

[LouNY]

I think Lou means loaded diameter, not radius.
But I'm curious why not replace them with the same tire again? Tire price is nothing compared to the expense that can happen with a 4wd and mismatched tires.

Often the manufactures will list a loaded radius measurement, then they also list an overall diameter. The loaded radius is what would be used to calculate a loaded circumference. Which would be the critical dimension .

I installed 26x12x12's on my 4410 in place of the factory 25x8.5 x14 tires. In 3000 hours the only issues I've had is wrecked tires from to low a ply rating. Going to 6 ply tires solved that. The tires are slightly larger but the only issue is that the front doesn't lead as much, which results in the front tires skidding on sharp corners. If it bothers me I just disengage the front wheels for corners. All in all the benefits outweigh the disadvantages.

I'm a bit confused you went with a taller?? front tire.
And your front tires are leading as much as the smaller tire did. They should be leading more if they are taller.

 

[rScotty]

Often the manufactures will list a loaded radius measurement, then they also list an overall diameter. The loaded radius is what would be used to calculate a loaded circumference. Which would be the critical dimension .

You're right. Neither one us should have used loaded radius OR loaded diameter - I'm not even sure that either of those have a physical meaning when we are talking about the loaded shape of a tire.

Loaded Circumference is the correct dimension to compare tires for 4wd lead/lag calculations.

rScotty

 

[pmsmechanic]

I'm a bit confused you went with a taller?? front tire.
And your front tires are leading as much as the smaller tire did. They should be leading more if they are taller.

Many years ago I had the same confusion, but a taller tire actually goes slower. Most front wheel assists have a certain amount of lead built in. A taller tire takes out part of that lead and I noticed that when I turned corners. I still have a bit of lead but not as much as I did before I installed taller tires.

I had it explained to me once and it made sense but I've forgotten the explanation. It has something to do with the circumference of the tire and the lead built into the drive train.

What I call lead is the difference between the front and rear tires. The fronts are geared so that they always pulling the rears slightly when engaged.

 

[rScotty]

Many years ago I had the same confusion, but a taller tire actually goes slower. Most front wheel assists have a certain amount of lead built in. A taller tire takes out part of that lead and I noticed that when I turned corners. I still have a bit of lead but not as much as I did before I installed taller tires.

I had it explained to me once and it made sense but I've forgotten the explanation. It has something to do with the circumference of the tire and the lead built into the drive train.

What I call lead is the difference between the front and rear tires. The fronts are geared so that they always pulling the rears slightly when engaged.

A taller tire does go slower. But lead/lag on 4wd assist is not about the relative tire speed between the front and rear tires. Lead/lag depends on how far the outer surface of the tire travels during one rotation of the axle, not how fast it spins.

Think of it this way: If the difference in internal gearing exactly matched the difference in tire (loaded) circumference, the lead/lag ratio would be zero. We can change lead/lag by changing internal gearing or by changing tire circumference. Tires are easier.

Increasing the height of the front tires increases the circumference of those front tires. And increasing the circumference of the fronts also increases the amount of ground that they cover in one axle revolution...so the taller tire has more lead, not less.

We spend a lot of time on lead/lag here on TBN because it matters for our 4wd assist tractors with their heavy front end loads and vastly different tire sizes. It sure isn't an easy concept to "see". If we had AWD and same size tires front and rear like an SUV or a Toolcat we wouldn't even have to think about it.

rScotty

 

[LouNY]

Many years ago I had the same confusion, but a taller tire actually goes slower. Most front wheel assists have a certain amount of lead built in. A taller tire takes out part of that lead and I noticed that when I turned corners. I still have a bit of lead but not as much as I did before I installed taller tires.

I had it explained to me once and it made sense but I've forgotten the explanation. It has something to do with the circumference of the tire and the lead built into the drive train.

What I call lead is the difference between the front and rear tires. The fronts are geared so that they always pulling the rears slightly when engaged.

Yes, but a taller tire is going to cover more ground for the same number of revolutions.
Because it is covering more ground for the same number of revolutions it is going to MORE lead then a shorter tire.
The tire with the greater loaded circumference is going to travel further for each revolution creating more lead not less.
A taller tire can turn slower to cover the same length of ground but if mechanically tied to a nother tire that will create a difference in either lead or lag.

 

[LouNY]

A taller tire does go slower. But lead/lag on 4wd assist is not about the relative tire speed between the front and rear tires. Lead/lag depends on how far the outer surface of the tire travels during one rotation of the axle, not how fast it spins.

Think of it this way: If the difference in internal gearing exactly matched the difference in tire (loaded) circumference, the lead/lag ratio would be zero. We can change lead/lag by changing internal gearing or by changing tire circumference. Tires are easier.

Increasing the height of the front tires increases the circumference of those front tires. And increasing the circumference of the fronts also increases the amount of ground that they cover in one axle revolution...so the taller tire has more lead, not less.

We spend a lot of time on lead/lag here on TBN because it matters for our 4wd assist tractors with their heavy front end loads and vastly different tire sizes. It sure isn't an easy concept to "see". If we had AWD and same size tires front and rear like an SUV or a Toolcat we wouldn't even have to think about it.

rScotty

Yep,

 

[pmsmechanic]

Like I say I don't remember the explanation that made sense to me. Both of you made an argument that makes sense on the surface but is wrong. A taller tire is slower, not faster. Again I don't know why but that's the way it works. My 25x8.5x14 tires have considerably more slippage in 4x4 then the 26x12x12 tires.

 

[rScotty]

With respect, I think you should go back and read what Lou and I wrote and then think about it.

It's polite of you to say that we "made an argument that makes sense on the surface", but that's doesn't help with mechanical things. Gearing and gear ratios isn't like sports or beer tasting where there can be different opinions on what works best. Gearng is mechanical; it doesn't have the luxury of opinions. It either works how it works, or not at all.

Mostly I find when all is said and done that the difference in mechanical explanations is in how things are defined rather than in how they work. That may be the case here. The "slippage" that Lou and I are talking about is a loss of traction between the tire and the ground when a tire skids due to torsional stress or "windup" in the gear train driving the front axle. The windup is caused by a front/rear drive ratio mismatch, and it will happen equally when driving straight ahead or when turning.

Side slipping on turns is different & can be due to several other things. That happens for lots of reasons. But adding the peculiar slippage due to a ratio mismatch will make the slipping while turning more noticible.

Bottom line is I don't care what you believe. I was just trying to get you to minimize the chances of a repair bill.

rScotty

 

[pmsmechanic]

Bottom line is I don't care what you believe. I was just trying to get you to minimize the chances of a repair bill.

rScotty

It's not what I believe that counts in this case, it's what I've observed. And since the tires now have less slippage in 4x4 that would be less strain on the drive train. It's been 19 years and 3000 hours.

 

[LouNY]

If it has worked that long the replacement tires where very close to the same loaded height regardless of the labeled size. Different brands and even different series of the same brand can have very different loaded radius.
Regardless of what you think you have "observed" a taller tire will have more lead then a shorter one. Possibly your original tire was lagging a bit and the taller if taller tire corrected that. It can be difficult to tell if a tire is leading or lagging and it often is not correct from the factory. Tire brands or series are changed during production as price and availability change. One of the tractors on the farm 18-20 years ago required 3 sets of tire swaps before they got the lead lag corrected on a brand new tractor. Engaging the 4wd would make the tractor slow down, disengaging and she would jump ahead. Took them 3 swaps before it was corrected.