The Mudcat Café TM
Thread #96401   Message #1885270
Posted By: JohnInKansas
14-Nov-06 - 12:29 AM
Thread Name: BS: Nitrogen in your Car Tires? Bull Or Not
Subject: RE: BS: Nitrogen in your Car Tires? Bull Or Not
While it's easy to reach conclusions based on simple "properties" of chemical substances, it becomes much harder to defend the conclusions against detailed and rigorous probing.

While Nitrogen is "less reactive" than Oxygen in many cases, Nitrogen does react with many other things under conditions (e.g. heat, pressure, and flow) that may well be present in something like an automobile tire.

Reaction products of Oxygen with Hydrogen, Carbon, and perhaps even Sulphur that may be part of the tire carcass are largely neutral (like rust), while reactions of Nitrogen with the same elements quite often can have strong acid/base properties. The tire rubber contains hydrocarbon chain molecules from which, with Nitrogen, NH3 (ammonia) may be produced.

Even if pure Nitrogen is used for an initial fill, the rubber is at least slightly permeable to both Nitrogen and Oxygen and the polymerized rubber itself most likely contains Oxygen, so HNO3 (nitric acid) could easily be formed. Add in the bit of Sulphur and one has a broad range of exceedingly nasty reaction products, containing various assemblages just of N, O, C, and S. (Most tire rubbers contain fairly large amounts of "carbon black" used both for color and for wear resistance, so there's no shortage of "essentially free" carbon to complete the nasties if the polymerized HC aren't enough.)

(I've omitted mentioning H2SO4 since it doesn't suit my argument. :>)

I'm not proposing that all this bad stuff happens; but I'll suggest that the simple arguments usually applied in this case are inadequate to be convincing without additional more rigorous studies that have not been done. (Or that at least are apparently not known to those doing the arguing.)

People have proposed filling tires with Helium, using most of the same arguments as for "pure Nitrogen." That one's pretty easy to deal with, since Helium passes through most rubber about like pouring water through a sock. In an enourmous gas bag like the Goodyear blimp you can get enough containment for useful performance due to the low surface to volume ratio, but you'd probably(?) never finish a race with useful pressure in ordinary tires using helium. (It seeps through most glass.)

To get the benefits claimed for Nitrogen, perhaps filling the tires with Argon would actually be better. I'm sure it's been tried; but I haven't seen the report(s).

The main benefit of using Nitrogen in racing is consistency and convenience. Many people believe in additional benefits, but for the most part those remain questionable when subjected to real examination. Most of the other "stuff" that's claimed comes down to deciding whether a marginal plausible effect is worth an additional demonstrable expense. Sometimes it is.

For ordinary automobile use, the convenience is in the opposite direction, and the cost is not capable of justification unless one wishes to just take it on faith that some vague "betterness might exist." (i.e. it makes you feel good to "buy into" something)