# Tire air pressure

**URL:** <https://community.cartalk.com/t/tire-air-pressure/34683>\
**Category:** Maintenance/Repairs\
**Tags:** pilot, tires, honda\
**Created:** [August 8, 2009, 2:43pm UTC](https://community.cartalk.com/t/tire-air-pressure/34683 "2009-08-08T14:43:37Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![rdevirg](https://avatars.discourse-cdn.com/v4/letter/r/71c47a/32.png) [@rdevirg](https://community.cartalk.com/u/rdevirg)\
**Post date:** [August 8, 2009, 2:43pm UTC](https://community.cartalk.com/t/tire-air-pressure/34683/1 "2009-08-08T14:43:37Z")

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When new tires are installed they are typically inflated off the car. The pressure is adjusted, they are bolted on and then the car is lowered to the ground. Why doesn’t the weight of the car increase the tire pressure?

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**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\
**Post date:** [August 8, 2009, 3:06pm UTC](https://community.cartalk.com/t/tire-air-pressure/34683/2 "2009-08-08T15:06:47Z")

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It does make some difference, but not enough to worry about. As the weight of the car is added it just changes the profile of the tyre so the total volume and pressure remains about the same.

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**Author:** ![twotone](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@twotone](https://community.cartalk.com/u/twotone)\
**Post date:** [August 8, 2009, 8:17pm UTC](https://community.cartalk.com/t/tire-air-pressure/34683/3 "2009-08-08T20:17:17Z")

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pV=nRT

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**Author:** ![CapriRacer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/capriracer/32/22_2.png) [@CapriRacer](https://community.cartalk.com/u/CapriRacer)\
**Post date:** [August 9, 2009, 12:01pm UTC](https://community.cartalk.com/t/tire-air-pressure/34683/4 "2009-08-09T12:01:06Z")

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It does - and at worst, it is 1/2 psi.

The real problem is tire growth. Believe it or not, but within the first 24 hours, a tire will grow enough to reduce the pressure up to 3 psi. Some knowledgeable tire shops will over inflate the tires so they can be adjusted downward later - but some overinflate just due to habit without really knowing why they do it.