Tire pressure for alternate size tires, is based on the oem tire spec pressure on the door frame placcard. You must:
1a) determine what the front tire
design load is in lbs, and the factory psi spec.
This info is on a placcard attached to the driver side door jam, at the lower rear location.
When it comes to the front design weight
(GFAW), the front is usually lower than the rear. This rear bias is due to the design condition, including 5 adults (3 in the back seat) and a bunch of luggage in the trunk.
You should use the rear design weight (from GRAW) only if you plan on loading the car as described. But for mostly 2 up at front and minimal trunk load, just use the front design weight for the front and the rear. And the rear is still lighter than the front, as evidenced by the tire sidewall bulge, so I put an extra 2 pis up front for even wear.
1b) On the oem tire sidewall you can read the tire's load capacity sec, like 93R XL, or 93R SL. It can also be read off the placcard for stock tires. If your new
tire size has this same load capacity on it, then you just use the front pressure spec in the rear, and ad 2 psi to it for the front.
2) If the load rating on the side of the new tire differs from the old spec, you need to see what pressure to put in the tire from the Official Inflation table:
Start at page B10 for 16" tires.
3) The placcard's GFAW is multiplied by 1.064 for the final front axle design load.
4) with the final design load (1/2 of the axle value) look up your exact tire and load spec to find what pressure to run. If that tire is weaker by 20 lbs or less, use it. If it's rating is low by more than 20lbs, best to find a stronger tire.