Originally Posted by m3alabama
You are correct that PSI is essentially PSI no matter what size, however a low profile 19 inch tire compared to a high profile 17 or even 18 inch profile has different inherent rigidity to the side-walls and less flex which means it requires different pressure to illicit the same type of feel and handling. Slip angles of the tires, grip etc is all different as side-wall flex changes. You need a higher PSI in a higher profile tire to create a similar rigidity of the side-wall to a lower profile tire with less pressure.
So while it does for some things it does not matter, handling absolutely will be different for the same PSI in a low to high profile tire
Actually, there's a way to determine the proper PSI for a different set of tires. Even if they're the same size as stock, PSI could be different. Check it:
Inflation of non-OEM sizes?