Given that the TPMS light generally comes on only when the tires are seriously underinflated, this is not a good approach to use.
Generally about 6 PSI low. not enough to cause any symptoms. Many people tire from seeking assistance when the warning light comes on, they begin to ignore it. Today I had a car come in with 20 PSI in the tires, the warning light must have been on for a year.
Actually, 1 PSI = 10ĀŗF is an approximation. The actual formula is more complicated. Over a range in temps and pressures, that varies from 0.80 to 0.93 PSI/10ĀŗF
For example at 28 PSI and 60ĀŗF initial, change is 0.82/10Āŗ PSI for change to 50ĀŗF
I have a spread sheet that does this calculation.
First convert temps and pressure to absolute (I used kelvins and Pa). Then use P2 = P1(T2/T1) for new temp to get new pressure, and convert to relative PSI.
But this does not take into account the small change in volume as pressure increases, ie the tire expands slightly as pressure increases.
+1
That is also my approach.
A slightly overinflated tire is not going to produce any problems unless one considers a somewhat harder ride to be significant.
On the other hand, an underinflated tire can cause damage to the sidewall, and that is something that should be avoided if at all possible.
The placard on my Outbackās door jamb specifies 32 psi front/30 psi rear. When the temps plummeted to less than 20 degrees a few weeks ago, I found that they were down to 30/28, so I used my compressor to bring them up to 34/32. When the temps rise, they will probably be something like 36/34, but that pressure is not problematic, and when the temps drop again, I wonāt have underinflated tires.
Temps fluctuate so much this time of year here in NH. With a week it sent from -5 to 60. Thatās a big enough swing to effect pressure.
I find it simpler to just convert Fahrenheit to Rankine. Simply add 459.67 to the Fahrenheit temperature and you have Rankine. No need to do a two step conversion first from F to C, and then C to K. Also, I convert psi gauge to psi absolute by adding 14.7 to the gauge reading.
Naturally, if you live on top of Pikeās Peak, that 14.7 number will be wrong.
Is it possible an average daily driver like me that gets air pressure checked at every oil change is negligent? Sorry you guys are anal retentive, but only 40 years under my belt and driving on without obsessing about temp and tire pressure.
Iāll have to say one thing, at -40, you wonāt have to worry about your tires overheating due to only being inflated to 23 psi.
Driving at highway speeds should warm them up to at least zero.
If Tom Bradyās football was inflated to a legal 12.5 psi in a 60 degree room, but the temps on the playing field was -40, the pressure would drop to an illegal 7.27 psi.
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Iāve been in Minnesota and South Dakota most of my life and I canāt say that I ever saw 40 below zero. 27 maybe but thatās about it. When it starts to get cold outside I just watch the tire pressure and when it gets a few pounds low due to temps, I add some air. Thatās about it for me.
I saw -40 once or twice. I was leaving the dorm in Limestone Me. one cold morning when I realized that I couldnāt breathe. I immediately put my hands over my mouth and exhaled and then was able to breathe slightly warmer air for a few breaths until I was used to the dry, cold air. 115 degree difference can be hard to take.
Iāve seen -30 and below a few times at 4am in the White Mountains. We usually get up that early on Sunday to head back south from skiing before the traffic picks up. Itās COLD. -40 isnāt unheard of either.
As I write this, the thermometer outside my office window reads -43ĀŗF. The official temperature, at the airport here (which is actually only about half a mile away), reads -47ĀŗF (feels like -60, according to www.wunderground.com). And itās only supposed to get colder today. Tomorrow itās supposed to warm up though: the high is -42ĀŗF, or maybe -36ĀŗF, depending on where you look 
Add to that a lovely ice fog that severely limits visibility, and you get the reason I posted this thread - I do not want to be dealing with a flat - or even just low tire pressure - in these conditions 
Iām not usually much of an advocate for Nitrogen in tires, but this seems like a perfect scenario for one. Wouldnāt it? A 100 degree shift in cold temp on the tires is not something I have any experience with (Iād move or set my self on fire to stay warm if it ever got near 0 degrees where I was, much less below zeroā¦) but nitrogen int he tires is there for this very reason- to keep tire pressures consistent.
that, and those snazzy green valvecaps.
Nitrogen is subject to the same laws for gases that air is. It does not maintain a constant pressure for changes in temperature. BTW air is 78% nitrogen and when pure nitrogen is put in a tire, there is already one ATM of air in there. To have 100% nitrogen in a tire, the tire would have to be filled in a vacuum chamber. At best, you will get about 91% nitrogen.
The only advantage to a nitrogen fill is that the nitrogen usually is dry, but there will still be some moisture in the tire from the air that is in there at the start.
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Keith is entirely correct. Use of Nitrogen has zero advantages.
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At that temperature, you could saw open your propane cylinder and pour the liquid propane out into a bucket.
Gotta be Alaska, Northern Canada, or Siberia. No place in the lower 48 have those kinds of temps that I can see. My sympathy.
Not many timesā¦but it does happenā¦
-30 in the White Mountain ski area is not unheard of. Iāve seen it more then once.
Yep, Alaska. Fairbanks, to be specific. Warmed up to -34ĀŗF this morning though, so not so bad 