Coming from an old [censored] here so take it for what it's worth...
PSI rating from the vehicle manufacture is best.
Working in a Fleet setting during the Ford Explorer recall and know for fact that vehicle manufacturers have safety in mind with PSI placards.
Adjustments to the required settings are supposed to be before the tire is up to operating temp. 35 PSI at a "cold" temp will climb substantially after driving. More during hot weather of course.
Starting off with a cold setting of 40 PSI results in a tire with 45 PSI after reaching operating temp. That can be the max according to some tire manufactures.
All of this is means nothing if tire sizes have been altered from original equipment specs.
Low PSI (for cushy ride) is what caused the Ford Explorer roll overs due to tires overheating/blowout and rolling over the sidewalls etc.
Too high can also create heat due to natural heat generated expansion and the weight of the vehicle rolling on a very small center tread patch area of the tire.
Neither scenario is worth the trouble.
Opinions are like a belly button...worthless but everybody has one
The heat thing is a bit far fetched, I think. I completely agree that pressure increases with temperature, that's simple physics. However, I've set my Volt's 215/55R17 tires at 40 PSI cold, and have never seen over a 3 PSI increase in pressure, according to the TPMS sensors. I observed this over a ~130 mile trip with speeds in the high 70's/low 80's and 90 degree ambient temps. The tires were filled at somewhere around 70 degrees ambient. It's been proven that under-inflated tires produce more rolling resistance, and therefore more heat.
Also, the "max PSI" pressure rating on the side of any given tire is a legal thing. Look how many tires have "45 PSI MAX PRESSURE" stamped on the side. C'mon... you want to believe that every tire made, in multitudes of sizes, has the EXACT same max pressure? It's no different than the gentleman's agreement between European cars way back when where they agreed to a 155 MPH speed limiter. 45 PSI is an extremely safe number, and I guarantee that any tire produced today can handle it, and probably 50 PSI consistently.
Keep in mind I'm not talking about a car that's towing, filled with 4 overweight adults, or otherwise compromised up-to and beyond it's capabilities. I'm talking about a regular vehicle in regular conditions with 2 average passengers. I, personally, noticed immediate tire wear on my Volt with the tires at the factory 38 PSI. The shoulders were wearing fast, and that was with 5k mile rotations and light driving. I upped them to 43 PSI cold, around 46-47 PSI hot, and the tires are wearing dead even. The electric range stayed the same, +/- a mile or two and the gas engine mileage is within 1%. I'm satisfied.
