[Dudesky]

Here's some info I found which may be of use here:

Some people aren't sure where to set their tire pressures. The one thing that is certain is that the maximum inflation pressure on the sidewall is not the right one to use. The vehicle manufacturer's recommendation is always a good starting point. It will be somewhere in the car. This used to be a sticker in the driver's door jamb, but more and more it's located on the back of the gas filler door. If that fails, the information should be in the owner's manual. Sometimes, there will be a range specified, or two different recommendations, depending on load. Anywhere between these numbers should be safe.

Changing the tire size or going to a plus-size fitment will change the required inflation pressure somewhat. Within the range of optional OE tire sizes, the vehicle manufacturer's recommendations should be followed. For sizes outside the range, the tire manufacturer should be able to help. Yokohama, for instance, includes pressure recommendations for stock and plus-sizes, by vehicle, in its annual Fitment Guide, which your tire dealer should have a copy of. Typically, these are 0-3 psi higher for a Plus-one or Plus-two fitment. Also listed are maximum load ratings at maximum inflation pressure for each size of each tire Yokohama makes.

If the recommendations you find leave you with a range and you want to know more specifically, you can experiment. Air, after all, is free. A change of 2-3 psi can completely change a vehicle. An underinflated tire will ride smoothly but feel sluggish, have mushy turn-in and go around corners with high slip angles or just not much grip at all. An overinflated tire will feel harsh on impact and over smaller bumps, and while responding crisply, will lack grip when pushed hard. To an experienced person, these characteristics are obvious even from the passenger seat. Try the minimum and maximum of your target range, and maybe slightly outside it, and decide what you like.

In the event that you aren't able to find a recommendation for your car, or the tires on your car are so different from those that were originally fitted from the manufacturer as to be incomparable, we received the following rule of thumb from Oscar Pereda, an engineer for BFGoodrich. He calls it a "realistic starting point," saying it has never been just right, but is a good place to start. The rule is:

(Vehicle Weight in lb/100) + 2 psi at heavier end + 2 psi all around if suspension and alignment are stock.

Example: Stock 911, 3,000 lb.
(3000/100) = 30 psi
Add 2 psi all around = 32 psi
Add 2 psi to heavy end = 34 psi at rear
With modified suspension, the result is 30 psi front, 32 psi rear.