Turf to R4

[tom39]

I recently purchased a 1987 B7200 with turf tires that I would like to swap out for R4's. The current tire size is 31-13.5 15 rear and 20.5-8 10 front. The issue I am having is that the rims on the rear are too wide to accommodate an R4. So I need to get a narrower rear rim to accommodate the R4. What I am thinking about doing is to just buy a complete set of rims and tires from a current Kubota model but I really don't know what model would have what I am looking for.

Does anyone know if there is a current model tractor on the market today whose tires and rims have the same bold pattern and would work with my tractors gear ratio?

Thanks
Tom

 

[tiredguy]

Tom,
your best bet is to try and get the information from a Kubota dealer
when it comes to wheels, they usually don't interchange as most
American tractors have always been with limited numbers of bolt circle
patterns. Kubota's are slightly different from model to model and they
may have different offsets too.

I'd ask them about the cost of ordering a set through the Kubota "whole
goods" program and see what the cost is new...sometimes not to bad at
all. Once you find out what they come up with the sizing still must be
confirmed by doing the math to make sure the ratio is the same. Just
because the "book" says there's different options DOES NOT mean that the
tractor doesn't require a gear change to make them work. I've figured a
few when then the outcome was that changing to the other tire options
would not work out without changing gears.
Al

 

[tom39]

Looks like the 2015 B2601 tire and rim set may work with a bit of modification. I have calculated the rolling ratio for both sets and the ratio calculates within 0.06 of each other. (The turf tires are 1.49/1 and the R4 tires are 1.55/1.) What do you all think?

If the ratio is acceptable, then the next issue I have is bolting up the front rims. The bolt pattern for the rear matches but the front does not. To solve this problem, my thoughts are to have a machine shop machine/punch/drill the correct pattern in the rims. Then I would have the old holes welded shut. What do you all think? Anyone else ever try to do something like this?

Thanks,
Tom

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[MadMax31]

Modifying the wheel sounds like a bad idea, but it could also be fine... Redneck engineering, right?

Sounds like a lot of BS just to have R4s on your machine. You on the pavement alot? Around here, R4 machines are pavement pounders...

 

[tom39]

Thank you for your response.

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[tiredguy]

Tom,
don't know how you came up with the numbers on what you found
so please post the sizes so we can see what they are.
The 0.06 will NOT work the difference has to be within 0.02 in order
to work without creating a problem with the ratio wrong. All about
the rolling circumference of the tires so that's what we need to know.

Personally I'd have to see the rims themselves to see if there was enough
"meat" in the centers to drill the bolt pattern needed between the existing
holes in them. Or the possibility of make a new set of centers for the rims
with the correct pattern and replace them cutting the existing one out welding the right one back in.
Al

 

[tom39]

Tom,
don't know how you came up with the numbers on what you found
so please post the sizes so we can see what they are.
The 0.06 will NOT work the difference has to be within 0.02 in order
to work without creating a problem with the ratio wrong. All about
the rolling circumference of the tires so that's what we need to know.

Personally I'd have to see the rims themselves to see if there was enough
"meat" in the centers to drill the bolt pattern needed between the existing
holes in them. Or the possibility of make a new set of centers for the rims
with the correct pattern and replace them cutting the existing one out welding the right one back in.
Al

So it has been quite some time since my last inquire but life seems to put things on hold sometimes. But here is where things are today.

I have the opportunity to purchase a used set of tires off of a 2007 Kubota. The tire size is 27x8.5-15 (front) and 15x19.5 (rear). Tire rolling circumference is 79" front and 122" rear.

The tires currently on my tractor are 20.5x8-10 (front) and 31x13.5-15 (rear). Tire rolling circumference is 58" (front) and 93" (rear)

Please correct me if my math is wrong on the ratio of the tires.
The used set would be:
122/79 which makes the ratio 1.6 to 1

My current set would be:
93/58 which makes the ratio 1.54 to 1

My hope is that a .06 difference in the ratio is not going to be to much of an issue. My other thought is that the tractor will not be operated on the road or asphalt unless I am crossing a road or clearing snow so stress on the drivetrain should be minimal.
But let me know your thoughts

Thanks
Tom

 

[tiredguy]

Tom,
assuming that the 79 & 122 RC is correct that ratio works out to .65.
Now looking back I double checked the 20.5-8x10 and I have the RC
on both at 61 inches NOT the 58 you got from your book. The common
OE tire was either the 20.5-8x10 Bridgestone PD or the 21-800x10
Firestone Turf & Field both having an RC of 61 inches.

So using the RC of 61 divided by the RC of 93 inches on the Firestone
31-1350x15 Turf & Field the ratio is .66 (rounded up). The difference
between the 65 and 66 ratios is 1.5% so it's within the 2% allowance.
66-65=1 divided by 66=1.5%. I don't have the specs nor do I know the
brand of the tires you're looking at buying but make sure you use those
mfg RC numbers to figure it out.

The size you found is WAY bigger than the original sizes it will look like a
monster in comparison and I seriously doubt that they would work for you
especially up front where room to turn sharp enough without rubbing has
to be taken into account plus the extra strain the bigger tires will put on
the front end. Jumping up roughly 6 inches in diameter is huge and the
rear tires are equally that much larger too. The change in the final ratio may result in not having enough power you need to work and the ground speed
would increase big time too. It's not like you're building a mud truck that
you can change from a small block engine to a big block to gain the power
needed to overcome the larger tires.
Al
PS: Rims would be a challenge to get too and those 19.5 diameter rears are
very expensive too.

 

[tom39]

Thanks for the help tiredguy. What I had been considering was a tire and rims set. The price was right at only a few hundred dollars. But it sounds like I may want to let this deal pass to someone else.

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[Yogihorseman]

HI I am new here and have a question I want to go from R4 to turf tires because the R4 just tear my yard up when I mow. The problem is my tires are 22X8.50-12 and all I can find in turf tires are 22X9.50-12, will this wider tire work?

 

[85Hokie]

HI I am new here and have a question I want to go from R4 to turf tires because the R4 just tear my yard up when I mow. The problem is my tires are 22X8.50-12 and all I can find in turf tires are 22X9.50-12, will this wider tire work?

Wider will not affect the rolling circumference, but when changing tire "styles" the rolling circumference can and will change due to how the tire is made. If wider on front, it could cause a rub when turning, if wider on back it could rub mmm or inner fender.

Best thing to do is measure YOUR tires RC - and that is easy....one way or the other. And then find out the RC of the other tire you wish to place on.

 

[Yogihorseman]

Anyone have R4 on the back and turf tires on the front ?
I called a dealer and he said you have to have the turf tires front and
back because of the four wheel drive any thoughts on this

 

[Burtonbr]

Anyone have R4 on the back and turf tires on the front ?
I called a dealer and he said you have to have the turf tires front and
back because of the four wheel drive any thoughts on this

Are you mowing in 4wd ? The fronts don't dig in as bad turning in 2wd, can you mow in 2wd in the area your talking about?

 

[Yogihorseman]

Yes I mow in 2wd and they dig in but not as bad as the would do in 4wd
the only way I can avoid digging in is to make long sweeping turns and that takes a lot of time

 

[tiredguy]

Yogihorseman,
As written above:
Best thing to do is measure YOUR tires RC - and that is easy....one way or the other. And then find out the RC of the other tire you wish to place on.

Yes you can put turf tires on the front IF you can find one that has the compatible Rolling Circumference needed. RC is the key to keep the front to rear gear ratio where it needs to be to avoid damage.
Al

 

[MadMax31]

Tractor data lists turfs for your machine, front 23x8.5x12 rear 33x12.5x15

Same as mine. I was looking into a set of AGs to have for field work, but I was looking around 1000 for correct wheels and tires. I have 3 sets of turf fronts but replacement rears are 350 a pop....