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.

[kaydeejay]

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.

[Alan_Hepburn]

Here ya go: Let me google that for you...

[DrewE]

jake2250 wrote:
You also need to factor in weight,, what are you loading that tire up with? Weight. outside ambient air, road surface temperature, speed etc! Oh and Altitude makes a bit of a difference!
Nitrogen will fix all of that and give you consistent pressures!

Are you suggesting that Nitrogen does not follow the ideal gas law? All gasses expand as their temperature increases, even nitrogen. The primary advantage of using nitrogen rather than atmospheric air is that nitrogen has less water vapor in it. (Air is, after all, mostly nitrogen.)

For tires, the pressure changes are due to changes in temperature inside the tire. Weight and speed only matter in as much as higher weight on the tire or greater speed cause it to flex more and heat up more as you travel.

[jake2250]

You also need to factor in weight,, what are you loading that tire up with? Weight. outside ambient air, road surface temperature, speed etc! Oh and Altitude makes a bit of a difference!
Nitrogen will fix all of that and give you consistent pressures!

[tarnold]

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.

[ajriding]

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.

[Beverley_Ken]

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

[Gonzo42]

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.

[MEXICOWANDERER]

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+