Tire sizing question

[ktpnw]

Question about tire sizing. My new-to-me 4WD Satoh Buck has 8-18 rear tires and 5-12 front tires, and those seem to be incredibly rare sizes, especially the rear. There is very little information about them and there seems to be not a lot of options in that size - even Rimguard's ballast fill calculator which claims to have over 2200 sizes in the database does not have 8-18.

I understand that due to the 4wd system I need to keep the ratio of front to rear size the same. But I am just wondering if there is another size that is equivalent (with a modern naming scheme or something), or if there is something else I'm missing, or if these are just truly a very rare and weird size.

The reason I ask is that I would ideally like to upgrade to either an R4 or R14 style. I need more traction than turf tires provide, but would like to be able to gently drive around on my flat lawn without tearing it up. If anyone is able to point me in the right direction, it would be much appreciated, and thanks in advance.

 

[Rockbadchild]

try 9.5-18, same size just wider

 

[sandman2234]

My thoughts are, find a chart or measure the rolling circumference of your tires and only upgrade using the same .
Figuring the ratio of the front to rear and what the change does if you want to increase or decrease both front and rears is more math than I want right now.
David from jax

 

[repete]

My thoughts are, find a chart or measure the rolling circumference of your tires and only upgrade using the same .
Figuring the ratio of the front to rear and what the change does if you want to increase or decrease both front and rears is more math than I want right now.
David from jax

A few years ago I gave up on finding a universally recognized "standard" for tire sizes. I had two tires on the rear of my L2550DT and they were both stamped with the same size. One was 3" taller than the other. I too was concerned for the drivetrain being not having the correct true ratio where the rubber meets the road.
If anyone finds an exact universal dimension chart I would love to see it. I would sure like my bucket to sit level...

 

[RayIN]

This might help: 8-18 BKT TR-171 Deep Tread Farm Tractor Tire (4 Ply) (TT)
It has a rolling circumference of 99", while a 9.5-18 has a rolling cir, of 104.2" and requires a wider rim.

 

[rScotty]

Sometimes it helps to know the actual rolling circumference on your tractor. To measure, put a blob of wet paint on the tire, and drive straight down a dry road in 2wd. Measure between paint marks.
rScotty

 

[470d]

Question about tire sizing. My new-to-me 4WD Satoh Buck has 8-18 rear tires and 5-12 front tires, and those seem to be incredibly rare sizes, especially the rear. There is very little information about them and there seems to be not a lot of options in that size - even Rimguard's ballast fill calculator which claims to have over 2200 sizes in the database does not have 8-18.

I understand that due to the 4wd system I need to keep the ratio of front to rear size the same. But I am just wondering if there is another size that is equivalent (with a modern naming scheme or something), or if there is something else I'm missing, or if these are just truly a very rare and weird size.

The reason I ask is that I would ideally like to upgrade to either an R4 or R14 style. I need more traction than turf tires provide, but would like to be able to gently drive around on my flat lawn without tearing it up. If anyone is able to point me in the right direction, it would be much appreciated, and thanks in advance.

Hey, I went through this brain twister a couple years ago and I think I figured it out.

When I got my 470 it came with the rice paddy tires on the rear and 5-12 on the front. 5-12 are pretty much impossible to find, I went into the manual trying to find out what the ratios are. Anyway, I ended up figuring out the ration between rear to front and got a 8-18 rear and 5.00-12 front tire, measured them and the ratio was perfect to what the book described.

So what happened, I installed the tires and took it for a spin on concrete in 4x4 and works absolutely perfect, I even realized that prior to this I had a little suttle stubble which I did not notice beforehand and must have been from slightly improper tire ratios, since you have to maintain the correct ratio in a 4x4 system due to different gear sizes or rotations per minute required by the rear transmission and front diff.

To summerize:

On a Satoh 470d front 5.00-12 and rear 8-18 seem to be the perfect ratios per manual.