I currently run 36x13.5x15 Irok bias ply tires(that are worn out). I was shopping around for replacements and really liked the IROKs so was looking for the same tire.

Now they have 2 tire sizes that are almost identical. A 36x13.5x15 and a 37x14x15. the exact dimension and weight numbers are slightly off and I couldn't understand why they would come out with two tires almost identical.

So I called Interco Tire and asked them. The answer? The molds that are used to make the tires are slightly off due to expansion/contraction of the mold during it's manufacture. That's the only reason they could give me. So I'm guessing, as demand for the tires increased, they had to create a 2nd mold to make twice the # of tires. But the mold came out slightly different.

I still don't like the answer I got but they said that was the only one they could give me.

My own guess is they originally mis-stated the size of the 36" tire(since it's diameter is 36.8" it should have been stated as a 37) and may have been losing a lot of sales of folks wanting to go to 37s. So they made a slight variation to their mold and called it a 37. Just a guess.




I now have a set of 37x14x16 bias plies. Looking at the tire, it doesn't have as much of a donut(sidewall bulge) effect that the 36x15s have but that could be due to rim diameter difference. The tread on the sidewall looks thicker and the main part of the tread doesn't have the large stickouts on the outter lugs the 36s had(I liked those large stickouts). So it appears the mold might have a few minor differences besides just the explanation I got from Interco.

Let me know if you have another answer on this.

Did you measures each tire before & after mounting (while new)?

I know many tires are actually smaller than their stated size....
I've seen the measurements new 35 Pro Comp MTs, 35 BFG MTs & 36" TSLs or SX (can't remember which) that were .5-1.5" smaller in height than stated.

Because of that, I've always assumed that they just round the stated tire sizes up.

I do know that my friends with Krawlers bragged to me when they got them that they were "true" to size (35" & 37").

Just a thought, but perhaps the Guvment has a break point on DOT approved tires? Or special testing that might be required to get DOT approval? Could be the answer why they marketed a 37" tire as a 36" tire....Ya never know.

Or it could be just a corporate fawk up. Either way, if ya like the tires, run the tires.

As far as sizes go, there is a big discrepancy between what's advertised and what it really is mounted. And rim width makes some difference to. My 32x11.50x15 TSL/SX tires measure 30.5" mounted on 8" wide rims. I was less than pleased when I saw them, but I needed some rubber to get the project 'rolling' around. I'll either go 16" wheels and metric tires, or with the 34x9.50x15 TSL tires when it comes time to replace them.

Anyone who's looked at the two tires side-by-side can see that the two sizes are clearly made in different molds. The 37x14 is noticeably wider than the 36x13.50 too. The 37 seems to be rounder in profile, mainly due to its additional width which pushes the sidewalls that much further out from the rims.

Interco has been known to change the stamp on a tire for marketing purposes before. One of the first 4 sizes created for the TSL was the 37X13. 37's were never a popular size in the old days. Sometime in the mid 80's, they came out with the 36X12.50. At this time, they did not have the 38.5X16. So, they simply rebadged the 37X13 - it's now known as the 38X12.50.