As Hank Hill says, “Always have two calibrated tire pressure gauges with you. Tire pressure is not something you want to monkey around with.”
So do you use the pressure recommended by the tire manufacturer, or the pressure on the placard inside the door of your vehicle? Because they don’t always match.
Typically, tires have a “maximum” pressure only on their sidewall, whereas the car will have a recommended pressure. And you should not ever go over the maximum pressure on the tire, of course.
However, you get into sort of a grey area when you replace tires. Lets say that a stock car with stock tires has a maximum pressure of 35 psi, and a recommended pressure of 30 psi. Now, lets say the car owner upgrades the tires to some z-rated ones with a maximum pressure of 45 psi. at first glance, inflating those to 30 psi as per the car tag indicates might be good, as it’s below the maximum on the tire. However, you have to assume, I think, that the real thing the car would “prefer” is a recommended tire pressure that is about 86% (30/35) of the maximum. So now one is left with the question, “do I inflate the tires to 38.6 psi, or something else? Does the relationship work linearly? Are there other factors that I need to be aware of here?”
Mercifully, tires have a substantial Factor of Safety on them, and you could be off by a bit and not suffer much for it, in reality. In the example above, I would likely round up to 40 psi, assuming the higher performance tires will work better at an operating pressure closer to their maximum, but I don’t have a handy cite to support that, that’s my educated guess.
There is no pressure recommended by the tire manufacturer. Tire manufacturers specify a MAXIMUM pressure which is not to be exceeded. Auto manufacturers determine the RECOMMENDED pressure for the vehicle/tire combination.
Thanks for the reply. I was definitely referring to the recommended pressure, of course. My reason for asking had to do with a.) the OP’s concern for the difference in pressure between cold/warm tires which I assume is going to be less than 2 psi and b.) my dad’s advice when I was a young’un to go slightly over the recommended because tires leak a little and slightly overinflating will give you a longer runtime between re-inflating the tires.
Not if you want to slightly over-inflate them the next time as well, it won’t.
and driving to the gas station takes less time than you may think…
My guess is you got ripped-off. Probably less gas stations charge for air than you use the pump.
Am I the only one (besides x-ray vision himself I presume) that thinks a lot off this discussion wouldn’t be necessary if this question were answered? 
It’s the smartest reply, and it seem totally ignored.
If the OPer check his tire pressure at home, and then when he got to the station, they were one lb off, then adjust accordingly.
My understanding is that it’s within a couple of PSI, and that anybody who has their tyre pressure that accurate is in a minority, and can rest easy.
Let’s say you run 32 in the front and 28 in the back, for example. You’ve done your research, and found that’s what you need. You top off the air weekly. You do everything by the book, except for ONE THING: you ignore hot versus cold, and just check the air when it happens to be convenient.
I’d say a person in your situation would have safer pressures than Joe “check-every-six-months” Average who has 10psi on one tyre, 35 on another, etc…
The Car Talk guys contacted tire manufacturers, and the advice is that you are much better off with over inflated tires than you are with under inflated tires. Problems related to heat build up, poor braking/cornering and tire fatigue are all associated with under inflated tires.
The consensus is that even at the max pressure printed on the tire, the consequence is a jolty ride, but nothing noteworthy as far as safety is concerned.
As a matter of fact, the Car Talk guys have had a long-running issue with another car guy who recommends that you run your tires near the max inflation. Tom and Ray even noted that the guy has data that shows that cars stop better, handle better and get better mileage, and they are actually apologetic for disagreeing with the guy, sticking to the ‘follow the manufactures recommendations’ approach. But more than once, they admit that the info about running tires at the max PSI is pretty impressive, but they just can’t bring themselves to concede.
Overall, under inflation is trouble. Over inflation might be better and is only a nuisance if you find the ride jolty.
I’d just like to note that if you’re checking your tires, make sure you check your spare at the same time, too. Be sure to examine the side of the spare for info, 'cause if it’s a doughnut, it’s likely to need 60 psi, not 32.
(If it’s under the back of the car, you might want to also make sure the winch mechanism isn’t rusted, like on my parents minivan. Or that it’s even still there, as the tow-truck driver had some stories where it wasn’t).
A man with one tire pressure gauge is sure of the pressures in his tires. A man with two is not sure.
To answer the OP, ask the experts the Rubber Manufactures Association.
So if the gas station is less than a mile from your house don’t sweat it. If it is over a mile measure the pressure at home and note just how low each tire is. For illustration let’s say your LF tire is 10 PSI low. When you get to the station, inflate your LF tire 10 additional pounds.
I changed over to a heavier duty tire on my SUV. BFG AT/KO. 8 ply load range D. In any case, the max pressure is 60psi. Recommended pressure on the car is 35.
These tires are quite a bit more heavy duty than say a standard street tire. But not at all unusual for the vehicle. I’m surprised that wildly different tires should have the same pressure.