Tire size ratio for L3430

[Fiddlin Farmer]

I need to replace the front tires on my L3430. The previous owner had 355/80D20 R3 turf tires on the back, and 27x8.50-15NHS R4's on the front. Is it enough to match the 27x8.5-15 when replacing the fronts, or should I be concerned about diameter variance between different brands of that size?

What is the proper front/back tire size ratio for an L3430?

How much variance (inches please) in the front tires would throw the ratio out of spec?

When I measured my existing tires, I came up with 42" diameter in back and 25" diameter in front. If I understand the calculations correctly, that means the ratio is 0.595. From what I have seen online, tolerance is generally accepted to be 0% to 3%, so making the diameter 26.25 would put my ratio at 0.625 which is a difference of 0.02976 which is practically 3%. Does this sound like the right math?

Is there a way to determine what the diameter of a tire is supposed to be based on the 255/80D20 or 27x8.5-15 numbers?

Thank you,
Fiddlin' Farmer

 

[kreuss]

Your math looks right to me. It's probably better to use the rolling circumference specification from the tire manufacturer than measured diameter. I think tire pressure will affect the measurements so there will be some variability.

I couldn't find my tractors front/rear ratio so I measured it myself. Jacked up wheels on one side, 4wd enabled and transmission in neutral, then rotated rear wheel a bunch of times and divided by number of times front wheel rotated.

 

[North Idaho Wolfman]

Yea measuring static diameter measurements especially on an R3 tire will not give you accurate numbers.

Here is the real issue, the original size for the tractor is a 27 x 8.5-15 R3 not a 27 x 8.5 -15 R4
those 2 tires do not have the same RC values.

Will it wear parts yes, will it wear tires yes, But will it work yes.

The only way your going to get it right is to replace both the front and rears at the same time, with the right tire combination.

The right R4 combination is:
10-16.5 R4
420/70/24 R4

 

[Fiddlin Farmer]

Your math looks right to me. It's probably better to use the rolling circumference specification from the tire manufacturer than measured diameter. I think tire pressure will affect the measurements so there will be some variability.

I couldn't find my tractors front/rear ratio so I measured it myself. Jacked up wheels on one side, 4wd enabled and transmission in neutral, then rotated rear wheel a bunch of times and divided by number of times front wheel rotated.

Thank you for the suggestion of looking for RCI in manufacturing specs. That helped a lot.

 

[Fiddlin Farmer]

Yea measuring static diameter measurements especially on an R3 tire will not give you accurate numbers.

Here is the real issue, the original size for the tractor is a 27 x 8.5-15 R3 not a 27 x 8.5 -15 R4
those 2 tires do not have the same RC values.

Will it wear parts yes, will it wear tires yes, But will it work yes.

The only way your going to get it right is to replace both the front and rears at the same time, with the right tire combination.

The right R4 combination is:
10-16.5 R4
420/70/24 R4

I'll start by saying I am on the other end of the spectrum from being an expert on tires - I know very little, but am working to learn.

So I found a couple of R4 sets and worked out the following:
firestone 10-16.5 R4 - RCI listing: 91"
firestone 420/70/24 R4 -RCI listing: 136"
ratio: 0.669

titan 10-16.5 R4 - RCI listing: 89.42"
titan 420/70/24 R4 - RCI listing 137"
ratio: 0.653

I called my local dealer and they said the factory turf option is:
bridgestone 27-8.5x15 R3 - RCI listing: 76.06299
bridgestone 355/80D20 R3 - RCI listing: 125.1181
ratio: 0.608

Given the bridgestone 355/80D20 R3's on the back that I don't want to replace, my front options (in R4, anyway) are:
titan 27-8.50x15nhs R4 - RCI listing: 80.11
ratio: 0.640

galaxy 27-8.50x15nhs R4 - RCI listing: 79.6
ratio: 0.636

The factory turf option looks like it has a much lower ratio - by 4.5% to 6% - compared with the R4 specs I found. The R4 replacement ratios are only 1% to 3% lower than the full R4 specs I found.

Questions:
* Seeing the descrepancy between ratios of the full R4 to the full R3, have I found some wrong RCI listings? Or is are the ratios supposed to be that different betweeen R3/R4?

* I have no idea why the previous owner put R4's on the front. Do you think I would notice any difference if I put R3's on the front?

Thank you,
Fiddlin' Farmer

 

[North Idaho Wolfman]

No I don't think you'll notice any difference.

What I have found is that the RC numbers for R3's tend to always be a little different then even r1's.
I think this might be that they are pulling back on the front lead to keep it from tearing up the grass.

If you've been happy with the performance keep what you have.
If your using a loader stay with the R4'S, as they will hold up much better.

 

[Fiddlin Farmer]

No I don't think you'll notice any difference.

What I have found is that the RC numbers for R3's tend to always be a little different then even r1's.
I think this might be that they are pulling back on the front lead to keep it from tearing up the grass.

If you've been happy with the performance keep what you have.
If your using a loader stay with the R4'S, as they will hold up much better.

Yes, between moving manure out of the dry lot, working on my driveway and trails, and moving dropped trees, I get a lot of use out of my loader. I mow a 4 acre pasture two or three times a year, but the R4 fronts have never been a problem out there.

Thank you for your help sorting this out - I really appreciate having this forum to learn from.