Temperature and tire pressure

[buck58]

I know a lot has been written about this already but, been parked for two weeks about to leave the nighttime temperature does it drop below 70°, my tire pressure, steer tires have dropped to 116 psi they should be 120, do I bring them up to 120 in the morning even though the temperature may be 70 or above? I’ve heard several schools of thought on the subject, but I’ve never heard a definite. I’ve heard tire should be aired up in the morning before you drive them it should be between 50 and 60° that obviously can’t have them in this case… and by the way that 116 psi is on my tire monitoring system I haven’t checked it with a gauge yet

[DoggieDaddy]

The charts talk about tire pressure at the ambient temperature which is 65 degrees.

[Gary.Jones]

Nope…. Leave them alone.

20~ 30 degrees different in the morning and it’s going to stay that ambient, probably adjust.

Gary

[rarebear.nm]

116 vs 120 PSI is about a 3% difference. There is generally no issue with tire pressures until a drop in excess of about 5% of the desired pressure. I would not even start thinking about it until I saw at least a 6 PSI drop.

This is a very common issue in the western mountains. You inflate at home in the valley say at 5,000 tp 7,000 ft elevation and drive to say about 10,000 ft elevation. In this example you may see at least a 15F drop in temperature and some drop in tire pressure. If I'm driving more at these higher elevations and staying there, I might top off the tires if I think my load requires it. However if I'm heading back down the mountain to lower elevations I know the tires are going to heat up and increase pressure. Likely back to what it was before the trip. What ever do not deflate a hot tire to try to stay within some pressure range. Tires are designed with these variations in mind and will not be an issue provided the tire is otherwise in good condition.

In short, IMO you have nothing to worry about. Leave them alone.

[K7JV]

Excellent advice, Fred!!!

So many of us over analyze everything, including tire pressures and loading.

Personally, I try to stay within a range.

1) It is very rare that I find myself letting air out to achieve a pressure.
2) If one or more drops below maybe 5%, as you said, I'll bring it up to the desired level.
3) I rely upon the TPMS for taking my pressure readings.
4) Every time we pull a cap and measure a pressure we create the possibility of valve contamination and the resulting slow leak so I don't touch those valves unless I really have to.
5) I do NOT get anal about a couple hundred pounds left to right on any axle. When you get down to it, fluids in the fuel, propane, fresh, gray and black tanks and road crowns have a lot more left to right effect than a few pounds difference we see on the level on the scales.
6) It's not likely we'll be able to move more than a few pounds of cargo/contents to make a significant difference.
7) I base my tire pressures on each axle to accommodate that axle's heaviest loaded tire(s).
8) Set those pressures based on the tables available from the tire manufacturer.

Beyond that, I try to just enjoy our new Entegra Esteem. ��

PS: In the news these days, all we hear is "follow the science". Well, I'll share some quick science. Pressure and temperature of a gas (air) in an enclosed and constant volume (tire dimensions don't change appreciably with the addition of two or three pounds of air pressure, though they do change some) and a constant number of molecules of that gas (you don't add air or bleed off any air) in that volume are inversely proportional. What that means is that you can multiply the temperature in Rankine (Fahrenheit plus 459°) or Kelvin (Centigrade or Celsius plus 273°) times the measured pressure in the tire and you will get a number. If you then divide that number by the new higher or lower temperature you will get the resulting pressure. Example: START OF THE DAY - Tire temperature = 50° and pressure = 100 psi. We calculate (50+459) x 100 = 50,900. LATER IN THE DAY, DOWN THE ROAD - The tire temperature has increased to 90°. We now calculate 50,900 / (90+459) = 93 psi. So as the day warms from 50° and our tires warm due to flexing while driving, our pressure increases by, in this case, roughly 3⅓%.

PS#2: If you have a tire temperature sensor that is mounted inside the tire, it is probably reasonably accurate. If it is an "add-on" that is mounted on the end of the valve stem, the temperature that it reports is often far more affected by the ambient air temperature and the fact that it is "in the wind" as the tire turns it's way down the highway than by the temperature of the air inside the tire. It's more of an indicator of outside air temperature than it is of the tire's temperature.

[rarebear.nm]

Jim, good points about the cap type TPMS sensors, of losing a bit of air taking them off/on. IN my case I use TST flow thru sensors. I have a accurate digital pressure gauge, +/- 0.5 PSI. I know that as the TPMS batteries age they seem to provide a lower reading. Thus I do not count on them as my primary sensor. I'll check with the digital gauge and then I know how close the TPMS is. I'm not knocking the cap type sensors, just different.

The main thing about any TPMS is catch unexpected tire pressure changes early.

I agree totally about the temperature on these external TPMS sensors. Temperatures vary greatly through out a tire while running at highway speeds. Temperatures will vary across the sidewalls and that is the most important temperature. Sidewall flex accounts for much of the heat build up within a tire.
These screw on sensors have no hope of providing a decent reading for the sidewalls. I wish the TPMS manufactures would drop the temp on the monitor and make the pressure numbers bigger.

[buddy110]

I realize each case is different, but FWIW, I run mine at 110-115 cold, no matter the temp