Tires: Calculating the correct tire pressure., correct tire pressure, passenger tires

Question
Dear Barry,

I have been crawling the internet all day in hopes of finding the elusive Correct Tire Pressure Formula for those of us who have switch from Passenger tires to Light Truck tires. The stock tire for my 4Runner were P265/70R17 113S and Toyota recommends 32psi on the door panel. I replaced them with LT265/70R17 121/118Q tires, which were initially inflated to 40 psi when installed.

However, I have no way to confirm or calculate if this is the correct pressure for my new tires and my new 4Runner. Can you help
?

Thanks!

Answer
Mike,

Absolutely, I can help.

What you need to do this are the load tables.  Unfortunately, they are copyrighted as this is the only source of funds the tire standardizing organizations can generate.  They sell this stuff in the form of a book.

But I have access to them.

At 32 psi a P265/70R17 has a load carrying capacity of 2425#, but because the tire is going on a light truck, the load capacity has to be reduced 10% to 2205#.

In order to carry the same load an LT265/70R17 has to use 44 psi.