Nascar, I'm old school and on my third X...
I also think of the door sticker as a guide only...
I always revert to the old "Chalk test" for proper air pressure for the conditions of MY vehicle and MY driving....
do a google search for chalk test for tires and you'll see others do too
NOW, I will bump it up a few pound if I'm on a LONG interstate drive where the rock hard tires will give me a BIT more mpg and no kidney pain... then lower it around town for a smoother ride...
good luck !
Here's some other info I found:
Calculating the inflation pressure when up sizing is a fairly simple calculation, but it requires the load tables, which are difficult to find. But there are several simple things:
1) The proper pressure for the original tire size is what is written on the placard.
2) If you are using the same Load index and have changed from SL to XL or vice versa, then the pressure is the same.
3) For every change in Load Index of 1, the pressure changes 1 psi in the opposite direction. Go from 93 to 96 and the pressure can be dropped 3 psi.
4) I don't recommend lower than 26 psi for passenger car tires, and 35 for LT tires. This is for bead retention during cornering
5) For passenger car tires, if the calculation indicates the need for more than 35 psi, then you need an XL. If the calculation indicates more than 41 psi, then you need a bigger tire size. For LT tires, don't exceed what is written on the sidewall.
6) For aspect ratios lower than 60, I think 3 more psi is needed to protect the rim from impact damage.
