Cold tire pressure vs hot

[tarnold]

Trying to set a tpms system. How much should a 225-75-16 tire pressure rise from 60psi cold to ?hot?, assuming outside temp of 70*. On the tpms you set for cold pressure. It will alarm at 15% . I wanted to alarm at a recognized 55psi. So if I set to say 63psi then it falls 15%, that would be around 55psi, or close enough. BUT coming from the tire store today it alarmed as high pressure and showed 73psi as the tire warmed up. Best I can explain it.

[wolfe10]

The Ideal Gas Law (which for centuries has stated the change in PSI for a given change in temperature) is for gases (like N, dry air, etc).

Water is NOT a gas and expands more than a gas for a given temperature rise. Does not have to be boiling for the pressure increase to be more than for dry air!

[ajriding]

Turning to steam? Where did this come from?
another chuckle.
idk, does humid ambient air expand with heat faster than dry air?

Tires can get hot from flexing a lot (overworking), but also from hot roads. Try driving through Palm Springs loaded in 120 degree temps when the pavement is probably 140+ and check air pressure. I've lost tires in this desert.

[philh]

2oldman wrote:
Hence the value of a good education.

sigh 😞

I value my MBA more than anything. I was blessed with an incredible mix of professors, whose sole goal was to teach us to question everything and trust nothing. Corporate finance prof was retired exec VP from federal reserve. 30 minutes spent on corporate finance, 2 hours 15 minutes spent on global macro economics in 2010. We had to learn the corporate stuff on our own time, but I wouldn't trade the global lessons for nuttin 🙂

[allen8106]

Mine usually read 10-15 pounds higher than cold.

[Ozlander]

Actually, if the tire pressure is rising more than 25%, the tire is telling you it working to much (sidewall flexing) to needs more air or less load.

[2oldman]

philh wrote:
If it's believed to be factually correct, it is assumed to be factually correct, and no amount of science can overcome this.

Hence the value of a good education.

[philh]

wolfe10 wrote:

CFerguson wrote:

Science (knowledge) matters.

And, its corollary: "An opinion expressed often enough/strongly enough does NOT overcome facts!"

I will disagree, there's actually "science" behind this. A lie told often enough is believed to be fact. Been awhile since I've seen the study, but it's something like 9 times. If it's believed to be factually correct, it is assumed to be factually correct, and no amount of science can overcome this.

[Dusty_R]

I carry a radiant thermometer and when we stop for a break I walk around our rig and check the temp of each tire.

[2oldman]

tarnold wrote:
Do you have to adjust all of your pressures thru out the day?

No. Perhaps you need a TPMS where you can set the alarm pressures.

[wolfe10]

CFerguson wrote:

Science (knowledge) matters.

And, its corollary: "An opinion expressed often enough/strongly enough does NOT overcome facts!"

[CFerguson]

kaydeejay wrote:

jake2250 wrote:
...........
Nitrogen will fix all of that and give you consistent pressures!

Nitrogen will fix NOTHING. You already have 80% nitrogen in there to start. As has been said, the ONLY possible advantage is that Nitrogen will be dry.

This is one of my favorite chuckles. If the N salesmen say that oxygen only is leaking out and the N wont leak, then a few top-offs of air will result in an almost 100% nitrogen environment inside the tire.
Science (knowledge) matters.

[philh]

Too funny...

Trailer tires will not get hot enough to turn water into steam. At ambient pressure that occurs at 212°F. Under pressure it's even higher.

Comparing our 65 mph trailer tires to those running 200mph is a hyperbole. Airplanes have the additional factor of being in subzero temperatures, which could turn to crystals and lead to an imbalance.

[fj12ryder]

tarnold wrote:
Op again. My tire traker is alarm at 15% low, 25% high, not changeable. Unit is advertised at +/- 2.7% pressure precision. So if I run cold tire pressure 60psi then: error of about 6psi either way. Only interested in low pressure, so if I set base pressure at 60 psi, alarm should sound at about 50psi considering error rate and 15%. But that means the high pressure could sound as low as about 70psi. Yesterday on a short drive with outside temp at less than 70* tire pressure went up to 74psi and high pressure alarm sounded. So on a hot day like Mex’s post, where do you set your base? Do you have to adjust all of your pressures thru out the day? Another’s rule of thumb would only be 3psi for a 30* temp swing?
Where am I figuring wrong.

This sounds like a very good reason to use a TPMS that allows you to set the limits to what you want rather than what they want.

With that setup I would set my pressure where I want it, and mute the alarm when it pops up.

[ajriding]

sounds like there is a discussion about apples to oranges…
Nitrogen in tires is 100% (or near) pure nitrogen.
Air in tires is air (mixed gasses) and water vapor.
The water will expand more than the gasses is what I found on a quick INTERNET SEARCH (never use gaagle).
Using this pure nitrogen gas must have a reason. Race cars, airliners use it. Nitrogen is used in racing shocks.
I guess you could use pure oxygen, but then you would have bigger dangers in the tire.
I guess you could try to dry out the ambient air you are putting in the tire first???
This seems a bit complicated topic for RVs