4wd tire size matching

bcny · Mar 4, 2021

I have a general question about the tire size matching front to back, to maintain the
front to rear axle ratios, on 4wd tractors.
Question is do the manufactures make the tractor with a single set of gears, or do they
change them to accommodate R1 vs R4's vs turf?
I highly doubt that they swap ring and pinion gears in the tractors just for the different tire options.
But what do I know, plus I am too lazy to look through parts books and see if different sets are called out
for the tire options. It could also be a set of gears in the "transfer case" or equivalent.
What is the industry practice?

FWY-my specific interest is a Kubota 4wd HST MX4700 with turf tires/wheels. Wanting to go to R1 ag tires/wheels.
This is a tractor I want to buy. I should have noted the current tire and wheels sizes but didn't, just that "it has turfs".
Inch sizes or metric, I don't know. 2013 model year.
Thank you.

BarnyardEngineering · Mar 4, 2021

It's all about maintaining the ratio of loaded radius front to back, within a certain tolerance, to prevent driveline bind-up and excessive wear.

If you put size X on the rear, you have to have size Y on the front. Going turf to ag, as long as you use the same nominal size, the ratio is maintained and things will work.

The tractor manufacturer should list the tire size options.

paul · Mar 4, 2021

It gets complicated when you have different tire manufacturers as well, folk just kinda try to get close then.

I believe it is needed to have the fronts slightly more aggressive than the fears, the drive lines can slip the fronts a tad. But it doesnt work well to have the rears pushing
the fronts around that binds up the drive lines with stress.

Paul

Dean · Mar 4, 2021

Any Kubota dealer will be able to answer your question (if they choose to take the time to do so).

They can also supply you with wheel tire sets to accomplish your objective.

Since the MX4700 is a current model, you can probably figure this one out yourself using the build it yourself option on the Kubota website.

Dean

mhb@ufe · Mar 4, 2021

As long as you use the ag tires that are recommended for that tractor you don't need to change anything else. The tire sizes in each category of tires has already been calculated by Kubota. The ones with computerized displays need to be programed for the tires that are installed for accurate speed readings.

Mark

495man · Mar 4, 2021

They aren't going to turn the same anyways, the front tires have to be oversped slightly so you can turn. The front tires have to be able to slip a bit, so don't run front axle of a hard dry surface like pavement.

If they turn the exact same speed, it's like a 4wd drive pickup trying to turn on a hard surface in 4wd.

showcrop · Mar 4, 2021

Unless you are roading a lot you would have to get pretty far off to notice any difference.

Traditional Farmer · Mar 4, 2021

The way to check out the 4WD and tires on older 4WD never done a never one is to park it on a concrete floor put it in 4WD,the transmission in neutral and roll it.If it rolls free the tires are right if it binds up they are off.

DoubleO7 · Mar 4, 2021

(quoted from post at 19:51:21 03/04/21)
They aren't going to turn the same anyways, the front tires have to be oversped slightly so you can turn. The front tires have to be able to slip a bit, so don't run front axle of a hard dry surface like pavement.

If they turn the exact same speed, it's like a 4wd drive pickup trying to turn on a hard surface in 4wd.

4WD pickups also "over speed" the front axle so that the rear end does not want to come around when going straight or turning.
typically you will have 4.11 gears in the rear and 4.10 in the front.

504 · Mar 4, 2021

One set of gears. As long as the over/under size is equal front to rear the tractor doesn't care. The local dealer up the street from me in town carried a complete set of turf,R-4s and tractor lug tires rims and all for the Kubotas they sold. THey said no matter what the tractor had on it, the buyer wanted a different set.

jimmyjoe · Mar 5, 2021

Kubota MX4700 Tires:
Standard tires (ag): Front: 7.5L-15. Rear: 14.9-26 (2WD)
Front: 9.5-16. Rear: 14.9-26 (4WD)
Optional tires (ag): Front: 7.5L-15. Rear: 13.6-28 (2WD)
Front: 9.5L-15. Rear: 13.6-28 (2WD)
Front: 9.5L-14.9-26 (2WD). Rear:
Front: 9.5-16. Rear: 13.6-28 (4WD)
Lawn/turf front: 29x12.50-15
305R343
Lawn/turf rear: 44x18-20
610R470
Industrial front: 12-16.5 (4WD)
Industrial rear: 17.5L-24 (4WD)

From tractordata.com

495man · Mar 5, 2021

(quoted from post at 18:22:51 03/04/21)

(quoted from post at 19:51:21 03/04/21)
They aren't going to turn the same anyways, the front tires have to be oversped slightly so you can turn. The front tires have to be able to slip a bit, so don't run front axle of a hard dry surface like pavement.

If they turn the exact same speed, it's like a 4wd drive pickup trying to turn on a hard surface in 4wd.

Click to expand...

4WD pickups also "over speed" the front axle so that the rear end does not want to come around when going straight or turning.
typically you will have 4.11 gears in the rear and 4.10 in the front.

May have been the case on some old trucks, but I believe anything new is identical.

I looked up my old F250 SuperDuty, Dana 50 front and Sterling 10.5, 3.73 ratio front and rear. You'll find replacement parts only come in the exact ratio the rear came in.

DoubleO7 · Mar 5, 2021

That is interesting as I looked to confirm that 3.73 is in front and rear on yours and you are correct.

But if you had 4.11 in rear, the only choice in front is 4.10 per torqueking.com

That was ratios of either new aftermarket or used oem.

Maybe it is a math rounding thing?

IaLeo · Mar 5, 2021

Did manufacturers get rid of "hop" under loaded field conditions. I have seen that problem some years back. Leo

timcasbolt · Mar 5, 2021

(quoted from post at 16:52:45 03/05/21)

(quoted from post at 18:22:51 03/04/21)

(quoted from post at 19:51:21 03/04/21)
They aren't going to turn the same anyways, the front tires have to be oversped slightly so you can turn. The front tires have to be able to slip a bit, so don't run front axle of a hard dry surface like pavement.

If they turn the exact same speed, it's like a 4wd drive pickup trying to turn on a hard surface in 4wd.

Click to expand...

4WD pickups also "over speed" the front axle so that the rear end does not want to come around when going straight or turning.
typically you will have 4.11 gears in the rear and 4.10 in the front.

Click to expand...

May have been the case on some old trucks, but I believe anything new is identical.

I looked up my old F250 SuperDuty, Dana 50 front and Sterling 10.5, 3.73 ratio front and rear. You'll find replacement parts only come in the exact ratio the rear came in.

Agreed. If a Chevy K series came with 3.42's in the front, it also had 3.42's in the rear. Same with 3.73's. The whole 4.10-4.11 thing is a new one on me. 4.10's are 41 ring, 10 pinion. 4.11's are 37-9. That usually means two different brands.

4wd tire size matching

bcny

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BarnyardEngineering

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paul

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Dean

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mhb@ufe

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495man

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showcrop

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Traditional Farmer

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DoubleO7

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504

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jimmyjoe

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495man

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DoubleO7

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IaLeo

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timcasbolt

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