Tires: Tire size/psi on sticker

Question
Hi Barry-

Ordered my 2001 Dodge Dakota 4X4 from the factory and ordered the optional wheels. The replacement tires I have now are TOYO A/T Open Country P265/70R16 with the max psi of 35 psi. The sticker on the door jamb says the tires are P235/75R15XL with a psi of 41. I always tell the oil change people to go by the tire and not by the sticker for the psi. The last time I had the oil changed the service adviser said I was sold the wrong tires and they were not designed for a pickup due to the low psi. Also he said the service guy will go by the sticker as that is what is the recommended psi by the auto manufacturer. When I got home I lowered the psi to the "max psi" on the sidewall. As I said before, I ordered the pickup new and it had 16" rims from the factory, why does the sticker say it has 15" tires? Should I go by the sticker for the psi or the sidewall? Are TOYO A/Ts not for a pickup?

Thanks,
Jim

Answer
Jim,

First, the information you are conveying to the oil change people is incorrect.  The vehicle tire placard lists the original tire size and the specified inflation pressure for that size.  If you are using a different size than listed, then that pressure is no longer valid and has to be recalculated.

But what is listed on the tire is of no value either, as it is a limitation of the tire and not a recommendation.

And what the service advisor told you is also incorrect.  Some trucks take tires at fairly low inflation pressure because the tires are bigger than the minimum!

So what is the proper pressure?  In order to carry the same load a P235/75R15 XL does at 41 psi, a P265/70R16 needs to be inflated to 28 psi.  However, there is a school of thought that say that if the load is matched at a lower pressure, use the specified placard pressure to maintain the tire's spring rate - HOWEVER, that's quite a jump up and I am uncomfortable with kind of change, so I say use a bit more - like 32 psi.

It's a bit complex, isn't it?