# Car tire pressure at high elevation

**URL:** <https://boards.straightdope.com/t/car-tire-pressure-at-high-elevation/958063>\
**Category:** Factual Questions\
**Created:** [January 19, 2022, 3:56pm UTC](https://boards.straightdope.com/t/car-tire-pressure-at-high-elevation/958063 "2022-01-19T15:56:05Z")\
**Posts on this page:** 1\
**Showing post:** 19

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [January 20, 2022, 11:39am UTC](https://boards.straightdope.com/t/car-tire-pressure-at-high-elevation/958063/19 "2022-01-20T11:39:04Z")

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> [@wolfpup](#):
>
> You’re probably right and I’m willing to take your word for it. FTR, my “1 to 2 PSI per 10°F” is cited at numerous sources, like **[Goodyear](https://www.goodyear.com/en-US/learn/driving-tips/tire-pressure-cold-weather)** , **[Firestone](https://www.firestonecompleteautocare.com/blog/tires/should-i-inflate-tires-cold-weather/)** , and **[tire dealers](https://burtbrothers.com/blog/how-temperature-affects-tire-inflation/)**. Some other sources claim an average of just 1 PSI per 10°F.

Actually it turns out I’m wrong because simple math is hard.

Ideal gas law says that for a body of ideal gas at constant volume, the pressure and temperature are proportional. This means that you can calculate pressure and temperature changes like this:

P1 / P2 = T1 / T2, or **P2 = P1 \* T2 / T1**

The trick is that all of those values have to be expressed in absolute. So for a tire starting out at 35 psi-gauge, P1 = 35 + 14.7 = 49.7 psi-absolute. And if it starts out at 75°F, then T1 = 75 + 459 = 534.

Now we drop the temperature ten degrees, to T2 = 524. So our final pressure is:

P2 = 49.7 \* 524/534

P2 = 48.769 psi-absolute, or 34.07 psi-gauge. (I forgot to switch the tire pressure to absolute, which is why my earlier answer was wrong).

So yep, about 1 psi per 10°F is the correct answer, assuming we’re dealing with typical car tires that are inflated to 30-35 psi. The 2-psi figure is a better match for truck tires, which are typically inflated to ~100 psi.

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