tire diameter

caterpillar guy · Oct 10, 2022

I'm looking for a rear tractor tire diameter chart for comparison of tire diameters. Found some 18.4R-42 would like to match them up to 18.4-38's thought since the duals are taller then the inside tires maybe I could put a set of 42's on the inside and the taller duals might not be to much difference in the field and turn easier on road and hard ground. They already have the step lugs for a 38to 42 change on the wheels.

Bob Bancroft · Oct 11, 2022

If you go to tire manufacturers websites, you can usually find tire spec's if you dig long enough. Static loaded radius, or the distance from the center of the axle to the ground is the important figure for height comparison.

Flat plate area, or footprint is another interesting figure. While researching tires for a sprayer, I found a 12x28 had a larger footprint than 11x38.

caterpillar guy · Oct 11, 2022

I was just trying to compare the height difference between an 18.4-38 and an 18.4R-42 what I came up with was only about 4 inches overall. I thought when they changed the 42 on my brothers 7140 they looked taller than just that 4 inches. Might have been just me.

cjunrau · Oct 11, 2022

https://commercial.firestone.com/content/dam/bcs-sites/firestone/PDF/RCI.pdf

According to this it has a difference of 219 inches to 207 inches per revaluation
That is 12 inches and seems to me that is way to much.

cjunrau · Oct 11, 2022

4 inches taller would be 12 diameter.

caterpillar guy · Oct 11, 2022

cjunrau So are you saying that one would scuff while the larger one would roll? I looked at your chart and it looked to me like with only and 1-1/2 to the side from center it would work in the field just roading might scuff the tread off from the smaller one with the RCI . I know on my semi trailers if I put a new tire against a half tread tire it would scuff the half tread bald rather quickly. There is a lot of difference in tire diameter from a 38 inch rim to a 22.5 rim though and speed is a lot different on a tractor versus a truck.

BarnyardEngineering · Oct 11, 2022

18.4x42's dualed up with 18.4x38's, the 38's won't touch the ground until things get soft. A 20.8x38 is a much better match to 18.4x42's, and in fact that is a common combination.

There is the circumference difference, but it's not like you're hooking up on hard pavement here. The ground will be loose and soft where the 38's will make contact, so they'll just slip a little more than the 42's.

Tire sizes are not "standard." Physical dimensions of tires of the same "size" will vary greatly from brand to brand, and style to style. You have to look up the loaded radius of the specific brand style and size of tire to get accurate information.

tire diameter

caterpillar guy

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Bob Bancroft

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caterpillar guy

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cjunrau

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