A co-worker asked me the other day what pressure he should fill his new tires on his car to. He had been confused by what he had heard, read as the maximum pressure on his tire sidewall, and what was in there now.
The suggested pressure in on your drivers side door. The tire pressure is actually based on your car, not which tires you have. The typical weight bearing load for consumer vehicles is somewhere around 32psi. In the meantime, your tire will say maximum pressure around 44psi.
The 32psi is cold.
The 44psi is ever.
But, there are some exceptions. When autocrossing or tracking, tire rigidity is more important than contact per se, and so to prevent tire rollover (particularly on weaker non carbon fiber sidewall tires) I will meet or exceed the maximum pressure in warm air. Also, a few psi in any direction won’t kill you. If you are going for high mileage on the highway and willing to sacrifice some traction on your wide wheels – then a few extra psi (~35, especially in the rear, won’t hurt you much.) And if you get stuck while offroading, you may try lowering your tire pressure down 5psi at a time until you can get out until about 15psi. Check to ensure that your overinflation isn’t causing the tire to crown – and your under inflation isn’t marking up the sidewall of your tires.
You can spend more on nitrogen air – but why bother? Nitrogen is a larger molecule than oxygen so less of it leaks out of your tires. It also contains less water vapor resulting in less expansion as temperatures change. But, if you are checking early and checking often (and I like to do a visual inspection whenever I get gas and before trips) than air will be fine (and more accessible.) For autocrossing, I used to use a 30gallon air tank – but then I learned that I can use a bicycle standing pump and it’s just about as quick and easy (with less weight to carry around).
[I take no liability in changes to your vehicle from this advice]