Tires: replacement tire for H 78 15 LT, maximum inflation, oasis travel

Question
QUESTION: I have an old Oasis travel trailer with H 78 15 LT tires
Universal Remington which need to be replaced.  Having trouble finding idenfication for replacement tires.  Please help.  Thank you.

ANSWER: Sherrie,

I'm going to bet the letters after the tire size are "ST" and not "LT".  So please check to see if that is true, because if it is not, then I'll need to do some digging.

And while you are at it:  Please get from the sidewall the "Load Range" or "Ply Rating". If the tire doesn't have that get the maximum load and the maximum inflation pressure.

---------- FOLLOW-UP ----------

QUESTION: FYI  LT is exactly what it is, but I have been assured that 225/75 15 6 ply will replace the H 78 15 LT tire.

Answer
Sherrie,

The reason I asked you to look for the letters "LT" is because this entry doesn't appear in any manual I have, but the "ST"'s do.  So if the tire is definitely an "LT" I have to pull some very old books out from the archive - which is probably going to take a week.

But if I can determine that the tires are indeed "ST"'s then I already have that info and can quickly answer your question.

But the issue about the Load Range / Ply Rating remains.  Unless someone actually saw that info on the sidewall, they can not tell you the a whatever 6 ply works.

So, please check the tire for both of these bits of info.


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Followup:

I have some not so old books on tire standards (circa 1990) and I wondered these might have something that would help me - and indeed they did - in the "Obsolete Standards" section.

An H78-15LT was in there and it says the tire has a diameter of 29.6", a width of 8.75" on a 6" rim, and a load carrying capacity for a Load Range C of 1830# at 45 psi (single, bias) and for a Load Range D of 2170# at 60 psi (single, bias).

Most trailer tires carry the designation "ST" in the size, so looking over the current standard for ST tires, I find that an ST225/75R15 has a diameter of 28.3", a width of 8.8" on a 6" rim, and for a Load Range C has a load carrying capacity of 2150# at 50 psi and for a Load Range D, 2540# at 65 psi.

I won't bother you with the math involved in converting an "LT" tire to an "ST" type tire, but the ST255/75R15 in the same Load Range as your current tire is a good fit!  Inflate it to the maximum (which is the way trailer tires work, but not the way car tires work!)