Nitrogen Inflation

In recent times there has been an increasing number of people promoting nitrogen as a medium for inflating tyres in preference to normal air.

The key arguments used in favour of this are:

• Nitrogen molecules are larger than oxygen molecules and therefore the use of nitrogen instead will negate the problem of slow deflation
• Nitrogen is more stable under changes in temperature hence maintaining a more consistent inflation pressure.
• More consistent tyre pressures will result in reduced fuel consumption, better tyre mileage and potentially also improved safety.
• Nitrogen contains less moisture and will therefore be less corrosive on the tyre and wheel.

All of the above may be true but the question is - to what degree and is the extra cost worth it?

The AA's advice on the subject is as follows:

Purified nitrogen has been used to inflate tyres on aircraft and racing cars for many years, but now some tyre specialists are offering nitrogen inflation for ordinary car and van tyres. The advantages of using nitrogen in specialist applications are clear " Planes fly at heights where temperatures may be as low as -40C. Any moisture in the tyres can freeze causing vibration and balance problems when landing. Pure nitrogen is dry so eliminates this problem (as would using dried compressed air) "

In motor sport the smallest fraction of a second can make the difference between winning and losing. Filling with nitrogen can reduce tyre pressure variation caused by changes in tyre temperature.

For passenger car applications the main claims seem to be " Reduced corrosion - because unlike air there's no moisture in pure nitrogen " Slower rate of pressure loss - because nitrogen molecules are larger than oxygen molecules (which make up 21% of compressed air)

Leakage can occur through the tyre's inner liner but can also occur through the valve, punctures, or failure of the seal between tyre and wheel rim. Pure nitrogen might leak more slowly through the liner, but regular checks of tyre condition and pressures will still be essential.

Corrosion of the tyre through use of normal compressed air alone is most unlikely because only the outer tread band of a car tyre contains steel - the amount of moisture reaching it from the inside is minimal.

Changing to nitrogen involves removing all the air which is already in the tyres and then re-inflating them with purified compressed nitrogen. There will be a one-off charge per tyre but once filled with nitrogen any future top-ups would also have to be with nitrogen if any advantages are to be maintained.

Overall, while accepting the possibility of purified nitrogen being of benefit in certain applications, we don't think that the cost and possible inconvenience are justified for normal passenger car use.