Tire Pressure

I try to keep my tires @ the 80 PSI COLD stamped on the side wall, and check them every time I roll. It has been two weeks since I've been out and the last time I checked the pressure it was close to 90 degrees. On my last trip I left early on a 40 degree morning and notice all the tires had lost about 4 to 6 PSI. Instead of firing up the air compressor I decided to air up the tires at the gas station a few miles down the road when I stopped for gas. After a short drive, when I got to the station, they all read 80 PSI.

In the cooler temperatures of winter should I air up the tires a little more???

Hi HornedToad,

80psi is the "cold" pressure where "cold" means the ambient temperature is 70 degrees (F), before you start driving, tires not in direct sun. If temps are lower, on an 80psi tire, you lose about 1.5 psi for each 10 degrees. At 40 degrees, you should be seeing a pressure of around 75psi. If it were 90 degrees you'd see around 83psi. After driving for a few minutes, the pressure climbs, often quite a bit.

On load range G tires, like the Goodyear G614 that we have, the cold pressure is 110psi and the change is closer to 2psi per 10 degrees. If I start at 110psi, after 15 minutes on the road, the pressure might reach 120psi. On a hot summer afternoon, it can go even higher.

I don't know the best answer but it was about 75 when I aired mine up a few months ago and are still holding the pressure. It is now colder and I have not corrected them, but the pressure comes up quicker than temperature of the tire once I start pulling it; so I am leaving mine alone unless I learn that I should not.

Not only does the air (ambient) temperature affect the tire pressure, altitude affects air pressure as well. So if you air up at sea level (or close to it) in the morning and drive to the mountains for the night, the tire pressure will be really different the next morning.

As Dan implied, the industry standard for a "cold" tire is 70*. Pressure is directly related to temperature, and varies with tire size, load, starting pressure and even altitude. Like Dan, my tires should be set at a max of 110 psi at 70*. At less than max load, they can be inflated to a lesser pressure. There are pressure tables for every size tire and load. Note that most rvs are heavier on one side and one axle may carry more weight as well; therefore, it is wise to set all tire pressures to accommodate the heaviest-loaded tire. A tire pressure monitoring system is an easy way to keep track of pressures and temps, even while driving.

Thanks for the reply, danemayer & all... using 70 degrees as the benchmark, as long as the variation stays within range, all is well.

HornedToad said:

Thanks for the reply, danemayer & all... using 70 degrees as the benchmark, as long as the variation stays within range, all is well.

Click to expand...

Great replies by all. I always consider the psi variance in the tires before setting out in the morning. If they are all near the same, I don't worry. If one is somewhat lower than the rest i dig a little deeper. Having a TPMS makes daily checks before travel very simple.

There should be a sticker on your rig (front left corner on ours) indicating the correct tire pressure at max weight. Just like your car, the tires are likely rated to a higher pressure than whats required for proper wear and brake effectiveness.

Once made a spreadsheet for it .
in part one pressure calculation with the same formula as the European tyre makers use.
In part 2 you can play with the inside tyre temperature to see what it does to the pressure.
Also you can chanche the outside pressure in milibar.
In part 3 you can give one temperature and pressure , and another pressure to see what the temperature becomes.
play with it and get wiser.

In next map on my public map of skydrive, take the pressurecalculationwithtemp spreadsheet at the bottom in xls , so for older Excell.
Also in this map my newest motorhome-tyre pressure calculator.
First download it by RIGHTCLICKING and then choose DOWNLOAD.
Dont use leftclick or open in web app or open in Excell, to complicated or goes wrong.
https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC!793

Here a picture to get the picture of how to use it.