# Car Tire Inflation

#81

Point is, you’re measuring the air pressure of the tires to on hundredth of a pound, but not factoring in the temperature of the tires before and after the drive. Without measuring the temperature too, you cannot know how much the altitude affected the pressure of the tires.

#82

If anything, the temperature at that NM ski resort was COLDER than the temperature in Texas which would have offset some of the pressure increase due to a higher elevation.
I had no thermometer with me to check tire temperatures but holding the back of my hand on the tires, they did not feel warm to the touch when I measured the pressure.
It wasn’t a precise scientific experiment, I just wanted to see for myself if my theory that high altitudes increase tire pressures was valid.
Atmospheric pressure at sea level= 14.696 psia
Atmospheric pressure at 8000 ft= 10.91 psia
That’s a difference of 3.786 psi. My tires gained about 3.5 psi according to my not laboratory grade tire pressure gauge. The difference could have been due to the fact that it’s hard to measure pressure without a small puff of air escaping no matter how fast I try to push the gauge on the valve stem, or the tire temperature could have been a little cooler when I measured it, or maybe I checked the pressure during high tide.
I’m pretty sure the atmosphere has tides just like the sea does, why shouldn’t it?

Even if your tires are inflated at the ragged edge of your TPMS trip point, pressure loss due to lower altitude likely won’t be detected because the sensors are completely inside the tire and thus they measure absolute pressure, not gauge pressure and absolute pressure in the tires does not change with altitude.

#83

I think we should all write to our congressmen and senators and demand the repeal of Charles’ law and Boyle’s law. Our tires would then stay at a constant psi and not be affected by temperature or atmospheric pressure.

#84

I bet you’d find some takers for the repeal, too.

#85

While we are on an anti-regulations kick, let’s stop demonizing dihydrous oxygen!