Tires: Calculating air pressures, Tire Inflation Pressure

Question
You stated earlier that a chart exists for calculating air
pressure, but not published due to copyright laws. Based on
that information, could you please calculate what the
corrected tire pressure might be for a 2000 Jeep Grand
Cherokee Laredo, 4 wheel drive, V8, with a factory tire size
of P225 75R16 and a replacement tire size of P245 75R16. I
recently installed new Bridgestone Dueler RVT tires all
around and wanted a little larger tire on the vehicle. These
tires seem a little low at 33PSI. The maximum pressure
indicated on the sidewall is 44PSI. Any help you could offer
would be greatly appreciated! Thank you very much.

Answer
Tim,

According to Tire Guides, a 2000 Jeep Grand Cherokee with P225/75R16's should have a vehicle placard inflation pressure of 33 psi.  Please check your vehicle tire placard to make sure this is correct as what I am about to write depends on that information being correct.  You can find the vehicle tire placard located on a doorpost, in the glove box, in the trunk or, on the fuel filler door.

So if that is correct, in order to carry the same load as a P225/75R16 does at 33 psi, a P245/75R16 needs to use 28 psi.  

So I am wondering why you would think 33 psi was low, especially considering the original pressure was supposed to be 33 psi.  Perhaps the maximum pressure is fooling you into thinking that is somehow a recommendation and not what it says it is - a maximum?  I cover some of this here:

http://www.barrystiretech.com/loadtables.html