Rear tire size question

Will a 11-2-38 fit on a 12-4-38? Im needing a rear tire or two for my H Farmall. Thanks

An 11.2 would normally fit on a 10" rim, and a 12.4 on an 11".
With bias rear tractor tires, you can go one size narrower or wider than what normally fits, unless you'll be near the maximum load for the tires.

11.2-38 = old 10-38; 12.4-38 = old 11-38 sizes. 10-38 "usually" found on 9" or 10" rims; 11-38 "usually" found on 10" or 11" rims.

Yes

According to the Tire and Rim Manufacturers Association, every tire has an approved rim width on the post 1954 tire sizing. Typically a rim one inch narrower than the tire cross section until you go larger than 16.9x38, which still needs a very hard to find 15 inch rim. The next larger tire, 18.4 takes a 16 inch rim and 15" is an approved alternate. 20.8's need 18" rims, 23.1's use a 20" rim, 24.5's use a 21 inch rim, and 30.5's use a 27 inch rim.
Going down in size, a 15.5" needs a 14 inch rim, a 13" would be first alternate. A 14.9 needs a 13 inch rim and 12 inch first alternate. 13.6 needs 12" rim and 11" first alternate. 12.4 needs 11 inch and 10" first alternate. 11.2 takes 10" and 9" first alternate. I think the "New size" for the old 9-38 is a 9.8x38, on a 9 inch rim, and 8" first alternate. We had a '40 JD B with 9-38 tires.

If you do a search on FIRESTONE COMMERCIAL tires you will get to a page that leads you to ag tires, may take a couple tries, I gave advice to FIRESTONE how to make their farm tractor website more user friendly, and they actually used a couple of my ideas. It's easier to navigate now than it was before. But ALL that information is available. I have tire data books for Good Year, Goodrich, Firestone, and Armstrong from my days at FARMALL buying tires. They all have static loaded radius, flat plate contact patch, etc.

I should also say that ill be plowing with it if that should make a difference

How wide is the rim ?

Interesting. Had no idea there was changeup in tire sizing. Think the 9-38 was the smallest 38 that was available for the H. Only ever seen one with those & it was on eBay almost 20 years ago. I recall thinking that there isn't a whole lot of tire there for cushion. Must have been a rough ride, but nice if you came from steel wheels.

Mike

There's another change in tire sizing going on right now. Outside of the US, the tires are listed in "P-metric" sizes like car tires. Most large radial tires for tractors are already using the "P-metric" sizing system.

Your 12.4x38 will soon be known as a 320/85R38.