Tire pressure low in high altitude cold weather

[incrediwoah]

So I assume its fine, but my tires in LA were at 42 and then upon getting to mammoth and parking it overnight the pressure dropped to 38psi prompting the low tire pressure alert. I assume its just because cold weather has less density, but do you recommend I go inflate it at the local station anyways while I am up here?

 

[Unpilot]

The tire pressure is related to the cold weather for sure. The recommended pressure is 45psi
I would recommend inflating them to 45psi when you get a chance. As you drive the air will heat up a little and expand. If they read 38 they will probably go to 40 or so while driving.

edit to say I have the 19" tires your tire pressure is on a sticker on driver side door jam.

 

[The Duke]

Agreed, add a couple of pounds if heading from warm to snow.
I have perfect tire wear at 41 PSI with staggered 21's and take them to 44 if heading to Tahoe.
If you want to get geeky: buy a tire pyrometer, drive your normal highway speed for 10 miles, quickly pull over and measure temperature at five points across the tread. Higher outside temps mean more air is needed, higher center temps mean less air. You want even tire temperature across the tire. If one side stays higher it's an alignment problem.

 

[jerry33]

If you want to get geeky: buy a tire pyrometer, drive your normal highway speed for 10 miles, quickly pull over and measure temperature at five points across the tread. Higher outside temps mean more air is needed, higher center temps mean less air. You want even tire temperature across the tire. If one side stays higher it's an alignment problem.

It's actually better if you have a helper to take the readings because tires heat up very fast once stopped and will throw the readings off.

 

[Snowstorm]

Can one use a FLIR camera instead of tire pyrometer?

 

[incrediwoah]

So I ended up inflating all of the tires to 44psi at the local gas station. I assume because it is cold right now, they will increase psi once I begin driving to a warmer climate?

 

[Barry]

So I ended up inflating all of the tires to 44psi at the local gas station. I assume because it is cold right now, they will increase psi once I begin driving to a warmer climate?

Yes. Tire pressure changes about 1 psi for every 10F. Living in a 4 season location, I routinely add air in winter and bleed some off in summer.

Altitude doesn't affect the pressure, however, if your TPMS sensors were calibrated at altitude the reading will be incorrect, as there's no external reference. For example, here in Denver, my TPMS sensors now read 3 psi low, as I had to re-calibrate when I replaced my tires. There's a longer explanation of this somewhere on the tirerack.com web site.

 

[incrediwoah]

Yes. Tire pressure changes about 1 psi for every 10F. Living in a 4 season location, I routinely add air in winter and bleed some off in summer.

Altitude doesn't affect the pressure, however, if your TPMS sensors were calibrated at altitude the reading will be incorrect, as there's no external reference. For example, here in Denver, my TPMS sensors now read 3 psi low, as I had to re-calibrate when I replaced my tires. There's a longer explanation of this somewhere on the tirerack.com web site.

Mine were calibrated in LA, so all good on that front! Ill probably be letting some out on my drive back. Thanks for the input!

 

[mongo]

@Cfinck

A few factors at play which other's have already addressed. There is the need to add air when the tires are cold, 68F to 20F would take 45 psi tires to 39.6 psi, so you would need to add 5.4 psi if the temp is staying the same for a while. But you are also at a higher altitude. Mammoth, CA is at 7,880 ft, so the ambient air pressure is 11 psi vs 14.7 at sea level. So the sensors will read 3.7 psi lower than the effective tire pressure due to that (so 41.3 readout is the same as 45 psi at sea level). Net result would be the need to add 1.7 psi to get to 41.3 psi.

Interesting regarding altitude adjustment, Tesla's don't have a MAP (manifold absolute pressure) sensor, but the GPS could be used to calculated the altitude offset.

 

[jbcarioca]

There are two factors involved:
Temperature and altitude. Both are directly caused by changes in ambient air pressure.
Ambient air pressure drops with altitude. If anybody wants it there is an easy to use chart available (every aircraft pilot must learn about this one. That means indicated tire pressure will rise with altitude increase for a given temperature, but;
Temperatures drop with altitude, and air pressure also drops with temperature. Cold tires always show less pressure than do warm ones. The same easy to use chart shows temperatures in relation to altitude also.
https://www.avs.org/AVS/files/c7/c7edaedb-95b2-438f-adfb-36de54f87b9e.pdf
the chart only shows standard conditions at sea level, so hotter temperatures are not in this chart.

In practice I add air if I am driving in very cold or very high conditions, and release the excess when I leave those conditions. Normally that might be a bit of overkill. Remember that the hotter the road surface the hotter the tire will be when driving, thus the higher the pressure will be. The opposite is also true. Other things remaining equal higher tire pressure will decrease heat build-up in the tire because there will be less sidewalk flex, which generates heat. Always, driving at high speeds and/or hot weather benefits from higher tire pressures, which are produced automatically.

I became unusually sensitive to these factors when I worked in a place where temperatures were sometimes 50C/122F and spent several months in a place where normal winter temperatures were frequently -20C/-4F or less. One quickly learns to adjust tire pressures differently in those two places.

 

[The Duke]

Can one use a FLIR camera instead of tire pyrometer?

I never tried it. Should work though.