# I got new tires on my car, but the tire store over inflated them. Is there a reason? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [June 9, 2022, 3:29am UTC](https://boards.straightdope.com/t/i-got-new-tires-on-my-car-but-the-tire-store-over-inflated-them-is-there-a-reason/965904 "2022-06-09T03:29:38Z")\ **Posts on this page:** 1\ **Showing post:** 22
**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:** [June 13, 2022, 11:00am UTC](https://boards.straightdope.com/t/i-got-new-tires-on-my-car-but-the-tire-store-over-inflated-them-is-there-a-reason/965904/22 "2022-06-13T11:00:55Z")
> [@Chronos](#): > > Shouldn’t be quite that much, but in that ballpark. Ambient temperatures will be around 520-530 F above absolute zero, so a change of 10 F is a little less than 2%. A 2% increase from a base pressure of 35 PSI would be 0.7 PSI. Presumably you’re talking about 35 psi-gauge, but for this math you need absolute pressure: 49.7 psi. 2% of that is 0.994 psi. Don’t feel bad. I made the same mistake just a few months ago: > [@Car tire pressure at high elevation](https://boards.straightdope.com/t/car-tire-pressure-at-high-elevation/958063/19): > > 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 + 45… --- _[View the full topic](https://boards.straightdope.com/t/i-got-new-tires-on-my-car-but-the-tire-store-over-inflated-them-is-there-a-reason/965904)._