LOL ok so when you remove factroy tire put completely different tire on so who tire pressure you going by?
Oh I'm glad you asked! This is a misunderstood theory that 99% of the people that you will buy tires from do not understand. I've been in the industry 10 years selling tires, and I've only really been aware of how to properly figure this out in the last 3 or so.
Bridgestone actually has a guide book called the "Replacement Tire Selection Manual" that spells it out for you with load charts!
Essentially it's all related to load rating, not really size, so let's assume that the factory tires here are the 235/50R18 97
W's. The 19 inch in question should be Pirelli Pzero Nero's 245/45R19 98
Since the load rating is numerically higher with the 19's, you could probably just leave the tire pressure the same as stock to duplicate the load capacity scenario in stock form (and that's what Ford does when they fit those 19's on there). According to the guidebook however, the 18 inch tire 97W tire carries 1532 lbs at 32 psi while the 19 inch 98 W tire carries 1488 lbs. At 33 psi, the 19 inch tire carries 1543 lbs per tire. Moral of the story, leave it at 32 and your fine, but according the tire manufacturer, in order to play it safe when fitting the non-stock tires, 33 is the proper pressure
for the new set to ensure mirrored load capacity.
The biggest thing that people miss is that P rated and non p-rated tires (also know as euro metric) of the same size and load rating can carry the same weight at different pressures.
Example - 235/50R18 97W vs P
Thanks for letting the tire geek rant!
2012 Mustang GT, Lava Red Metallic, Brembo, 401A, Cashmere leather, pedestal spoiler and hoodscoop. Mods - Boss shift knob, Weathertechs, GT fender badges, Steeda Ultra-lites/Tokico's D-specs/Steeda HD mounts & phb/GT500 iso's, 20% tint, Steeda UCA, Roush Axlebacks, Bassani X-pipe, no reso's, Painted lower valances, Boss mudflaps, MMD hood struts, MGW shifter, 275/40R19 Michelin Super Sports all around, Whiteline Sways/LCA's/Brackets, Steeda CAI, Bama 93 tune.