this is I found on the net...
*"Always go by the Tire if the tire has been changed from the original set.
It is best to keep the tire at about 10% the maximum fill." *

on my vanagon with General Grabber the max on sidewall is 50psi - minus 10%
will give 45psi, I put 46psi which is about right. (for the Rear)
as for the Front...  for weight distribution and comfort I subtract 20%
which came about 40psi, I put 42psi.

now if you decide to put as recommended Max psi on the sidewall... Fine,
Bravo  and be Happy...

peace...