My tires should be inflated to 30 PSI when cold. If I want to check it after driving over an hour what should the reading be when hot?
This is variable as it depends on the ambient air temperature; the temperature of the road surface; whether the road surface is asphalt or concrete; the speed at which you have been driving; how much brake heat has transferred to the rim; the load on the tires; and even the make of the tire itself. If you needed to know the 1 hour driving pressure you are going to have to measure it at the time and note it for future reference. Also as part of the inspection, observe the temperature of the tire by putting your hand on each tire or using a noncontact temperature gauge to see if there are any inconsistencies.
In the desert, probably an additional 5 or 10psi (A wild guess).
In North Dakota in the winter, 30 psi. At -20 degrees F ambient, and with the tire and wheel moving through the -20 degree air (the metal wheel dissipates heat too), the heat dissipates faster than it’s generated. I guarantee it.
Although, the more I think about it the more I realize that the tire in the desert started out at 30psi at desert ambient temperature and the wheel in North Dakota started out at 30psi at -20 degrees F. So, we’re really only talking about dissipating the additional heat generated by friction and that “temperature change” should be similar regardless of the temp the tire’s air started at. In short, if the temperature of the tire’s air rises 5 degrees in the desert it should also rise 5 degrees in North Dakota.
Is this a trick question?
Pressure buildup should be considered as an upper limit, not a target value - lower pressure buildup is always better (for street tires).
Normal upper limit for build up is 3 psi, but 5 psi can be tolerated. If you get more than 5 psi you should add more pressure. Be sure you do not to exceed the cold limit as stated on the sidewall of the tire whebn the tire is cold. (It’s OK to exceed it hot, but as I stated no more than 3 to 5 psi above the value hot.)
BTW this works regardless of what the ambient temperature is outside. Don’t forget, the cold pressure is set at the ambient temperature.
My 2000 Blazer’s tire pressure (235-70R15) increases about 3 PSI after a 10 or 15 minute drive to the gas station, maybe 2 PSI in the winter. I overinflate the tires (but less than the max pressure on the sidewall) at the gas station and do the final adjustment after I get home and let the truck sit for a few hours.
I know. I realized the error of my reasoning as I was writing. I went ahead with the original logic to demonstrate its fallacy…and just for fun.
Yup, it turned out to be a trick question…although I don’t think the OP meant it that way.
Glad you posted.
If you check them cold and then hot, you will know.