Tires: tire pressure, nissan frontier, oversized tires

Question
Dear Barry,

I just bought a 2001 Nissan Frontier.  This is my first experience with a pickup truck.  It seems to have oversized tires on it and I'm unsure of what the tire pressure should be.  Here is a bunch of info I got from the tire itself:

All Terrain Pathfinder
M + 5    30 X 9.5 OR15LT
Range Load C
Max Load 900 kg
(1985 lbs at 350 kp8)
50 psi cold  

I've read your past posts and if I'm correct, the pressure is keyed to the vehicle type, not the tire itself.  

The info on the door panel reads:

with p 225/70R15 tires 15 X 6.0   rims at 26 psi cold

I'd like to inflate as high as possible (for gas mileage) but without robbing the truck of traction.  

This isn't so easy for a lay person to figure, so I thought I'd ask someone like you.  Thanks very much!

Best,

Paul Myers  

Answer
Paul,

You did a great job of research, which makes my job a lot easier.

If your placard says the vehicle came with P225/70R15's at 26 psi, that equates to a load carrying capacity of 1383 #.  Please note my book says the placard should say 26 psi on the front and 29 psi on the rear.  Please check this out.

A 30X9.50R15LT requires 30 psi to carry the same load for the front and assuming I am correct about the rear - 35 psi there.  I usually recommend between 3 to 5 psi more than the placard to improve fuel economy.

EXCEPT!!!  A 30X9.50R15LT requires a minimum of a 6.5" rim and you have a 6" rim.  This is going to cause the tire to "arch" and ride in the center - not good!

For safety reasons I'd recommend using the tire at 30 / 35, but be aware that the tire is somewhat distorted and if you have an early opportunity to get tires that are appropriate for the rim - do so.