Many people have their own ideas on the use of Nitrogen in tyres, so it can be hard to separate the facts from the myths. Some tyre fillers are even making greatly exaggerated claims to their customers of savings of up to $500 if they use Nitrogen.

They hope that this will bolster the revenue collected from charging for these value-added sales. To ensure that your neither shaken or stirred by these stories, it would be good for us to examine some of the facts behind this trend 

The Facts

Hydrogen was discovered in 1772 by a chemist, Daniel Rutherford, and it makes up 78.1% of the air that we breath. Oxygen makes up 20.9% of our atmosphere, while the rest is composed of Argon, Carbon Dioxide and other gases.

One of the claims made about Nitrogen is that it runs cooler and doesn't expand as much as other gases when heated. This quite simply, is a myth. Using the "Ideal Gas Law" we find that all gases in common use have exactly the same thermal expansion characteristics. If their volume is fixed, their pressure increases by exactly the same percentage, for every

degree Celsius temperature rise (PV=nRT).  

This situation is changed however, if there is any water vapour in the air that is pumped into the tyre-Much of this vapour condenses onto the inside of the tyres. As the tyre heats up, this water vaporises and adds to the already increased pressure from the expanding air. The amount of moisture in the tyres can vary greatly and this is reflected in the inconsistent results we can get when checking tyres at operating temperatures compared to when

they are cold.

The effect of moisture is the major reason that most racing cars use nitrogen to inflate their tyres. The few that don't, use dried compressed air to eliminate all moisture.

The requirements of a race car are different from that of your average family car. On a race car the tyres don't stay on the rim for very long, where as on a passenger vehicle they are usually expected to be there for years. It is in this environment that we get the slower effect of pressure losses caused by air molecules passing through the tyre wall. Oxygen has

smaller molecules than Nitrogen and diffuses much quicker through the rubber of the sidewall.

It has been shown that Nitrogen filled tyres lose pressure around three times slower than those filled with air. This constant pressure loss contributes greatly to abnormal tyre wear and to additional maintenance of tyre pressures.