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.

You should factor in what summer temps are going to do to the pressure. I've seen my 11:22.5 go from 90 lbs to 122+

A good rule of thumb which I use is that for each 10 deg F rise in temperature, the tire pressure will rise 1 psi.

On my TST system, the defaults were minus 10% and plus 20%. For my rear tires , cold pressure 80 psi. The low alarm would go at 72 psi and high pressure at 96psi. I changed the high pressure alarm to about 104, because of driving in 100f temps. The side in the sun were just over 100psi, but the shady side stayed around 95 , 96 psi The high temperature alarm was defaulted to 160f. My tires were close to alarming that day as well. That temperature did agree with my infrared temp, I also checked a couple of parked trucks and there temps ranged from 170-180 on the driving sunny side. I’m much more concerned about low pressure than the highs, so I reset the low pressure alarm to 75 psi. Also the appropriate change for the front axle where I run 65 psi Ken

Side note, tires are rated at double what is stamped on the side - because they know heat and hard use will increase the temps inside the tire. 80 psi tire new should handle 160psi without blowing up. An older tire will blow up.

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.

Cold tire pressure vs hot | Good Sam Community

wolfe10
Explorer
Mar 20, 2019
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
Explorer II
Mar 20, 2019
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
Explorer II
Mar 19, 2019
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
Explorer
Mar 18, 2019
Mine usually read 10-15 pounds higher than cold.
Ozlander
Explorer
Mar 18, 2019
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
Explorer II
Mar 18, 2019
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
Explorer II
Mar 18, 2019
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
Explorer
Mar 18, 2019
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
Explorer II
Mar 17, 2019
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
Explorer
Mar 17, 2019
CFerguson wrote:

Science (knowledge) matters.

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

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