# Is it better to fill your tire with oxygen instead of air? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [October 2, 2007, 10:16am UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242 "2007-10-02T10:16:38Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![megas\_alexandros](https://avatars.discourse-cdn.com/v4/letter/m/e95f7d/32.png) [@megas\_alexandros](https://boards.straightdope.com/u/megas_alexandros)\ **Post date:** [October 2, 2007, 10:16am UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/1 "2007-10-02T10:16:38Z")
I’m new here, so i don’t really no what I’m doing, but I noticed that in this column: [http://www.straightdope.com/columns/070216.html](http://www.straightdope.com/columns/070216.html) cecil says nitrogen effuses (exits a small leak) slower than oxygen. But N2 weighs less than O2, so by graham’s law of effusion and common sence, nitrogen should escape the tire faster. ---
**Author:** ![megas\_alexandros](https://avatars.discourse-cdn.com/v4/letter/m/e95f7d/32.png) [@megas\_alexandros](https://boards.straightdope.com/u/megas_alexandros)\ **Post date:** [October 2, 2007, 12:04pm UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/2 "2007-10-02T12:04:26Z")
oops, i meant nitrogen in the title ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [October 2, 2007, 1:15pm UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/3 "2007-10-02T13:15:07Z")
Welcome to the Straight Dope Message Board, **megas alexandros**! Other than the mixed up title to the thread, you did just fine! You posted something important to say, and you included a link to the article under discussion. 🙂 Stick around: someone will be along in the very near future to address your comment, no doubt. Pull of a chair and poke around the other fora; we’re kinda fun if you let us grow on you. 🙂 ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [October 2, 2007, 3:57pm UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/4 "2007-10-02T15:57:58Z")
[QUOTE=megas alexandros] I’m new here, so i don’t really no what I’m doing, but I noticed that in this column: [http://www.straightdope.com/columns/070216.html](http://www.straightdope.com/columns/070216.html) cecil says nitrogen effuses (exits a small leak) slower than oxygen. But N2 weighs less than O2, so by graham’s law of effusion and common sence, nitrogen should escape the tire faster. [/QUOTE] [This PDF](http://www.getnitrogen.org/pdf/graham.pdf) explains it. Briefly:[ol] [li]Graham’s Law applies to effusion, not to permeation through a solid (such as rubber).[/li][li]The key factor in permeation is molecular size.[/li][li]O[sub]2[/sub] is smaller than N[sub]2[/sub]. There is no obvious relationship between atomic number or atomic mass and atomic diameter. See [this diagram](http://www.crystalmaker.com/support/tutorials/crystalmaker/resources/VFI_Atomic_Radii.jpg).[/li][/ol] ---
**Author:** ![megas\_alexandros](https://avatars.discourse-cdn.com/v4/letter/m/e95f7d/32.png) [@megas\_alexandros](https://boards.straightdope.com/u/megas_alexandros)\ **Post date:** [October 3, 2007, 1:15am UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/5 "2007-10-03T01:15:59Z")
OK, that makes sence ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [October 10, 2007, 3:25pm UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/6 "2007-10-10T15:25:13Z")
[QUOTE=John w. Kennedy] O2 is smaller than N2. There is no obvious relationship between atomic number or atomic mass and atomic diameter. [/QUOTE] Actually, the relationship is that the radius decreases to the right due to increased charge on the nucleus. Also, since both N[sub]2[/sub] and O[sub]2[/sub] are diatomic, their atomic radius may not be the size determining factor. O[sub]2[/sub] has effectively (minus a small amount of anti-bonding from the HOMO) a double bond, while N[sub]2[/sub] has a triple bond. Typically, a triple bond will be shorter than a double bond so it might be expected that N[sub]2[/sub] is smaller. I don’t know what the actual numbers are so O[sub]2[/sub] may be smaller, but referring to the atomic radius for the size of a molecule is wrong. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [October 11, 2007, 5:42am UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/7 "2007-10-11T05:42:34Z")
It’s a lot better for the profit margins of the people selling the nitrogen. But there’s no evidence to show it’s better for the buyers. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [October 12, 2007, 1:32pm UTC](https://boards.straightdope.com/t/is-it-better-to-fill-your-tire-with-oxygen-instead-of-air/421242/8 "2007-10-12T13:32:13Z")
[QUOTE=John W. Kennedy] The key factor in permeation is molecular size. [/QUOTE] Yes and no. In this _particular_ instance, comparing the permeation of N[sub]2[/sub] and O[sub]2[/sub] through rubber, “[t]he differences observed are essentially solely due to the slight differences in the size of O2 relative to N2.” (from your pdf) In general, _a_ key factor is the molecular size, but in addition the solubility of the gas in the material must be considered: “[D]ifferent types of gases will permeate each material faster or slower depending on the relative sizes of the gas molecules, _as well as on how soluble the gas is in the solid material._” (also from your pdf; my italics]