Nitrogen Tyre Inflation

Reasons we do not recommend

There are no discernible benefits for ordinary road cars

  1. After researching many web pages and sources about using Nitrogen to inflate car tyres I summarise the information I have found here.
  2. Car tyres are normally inflated with compressed air.
  3. Air is approximately 80% Nitrogen, 20% Oxygen.
  4. Nitrogen is comparatively inert, Oxygen is a reactive gas.
  5. The Nitrogen used for inflation in tyre depots is normally generated by a separation process from compressed air. It still contains about 5% Oxygen.
  6. Nitrogen used at race tracks and in industry may be 99%+ pure and contained in high pressure cylinders at 2000+ psi.
  7. Both sources of Nitrogen will be treated to reduce the amount of water vapour.
Claims Answers Explanation
Nitrogen filled tyres hold their pressure for longer than normal air WRONG

(as far as tubeless car tyres are concerned)

Research Data from Dupont shows that although Oxygen is the heavier element it does leak through a porous rubber membrane faster than Nitrogen, but the rate for both gases or a mixture within a tubeless rubber tyre which has an IMPERVIOUS liner is so slow that it would take SEVERAL YEARS for all the oxygen in an air filled tyre in good condition to leak away: though greater leaks can occur around the rim-to-bead seat – so the answer here is to ensure the tyre is properly fitted and sealed.

Test Data from Consumer Reports in the USA, who tested 60 car tyres half filled with air and half with 95% Nitrogen, showed that over 12 months the air filled tyres lost an average of 3.5PSI but Nitrogen filled tyres lost only 2.2PSI. This difference is 1.3PSI and not significant over a year given that tyre pressures should be checked and topped up weekly or monthly depending on usage.

Many tyres used in the earthmoving and mining industries still use tubes in which case the leakage data and benefits of Nitrogen may be more relevant.

The inner lining of the tyre and the wheel do not become oxidised or corroded or perish if filled with Nitrogen WRONG

(as far as tubeless car tyres are concerned)

Given the average life span of a normal car tyre is 2 to 5 years, depending on use, and the average life of a vehicle is 10 to 15 years, the amount of corrosion of the wheel or degradation of the inner tyre lining from the oxygen in the air is not measurable. The only time significant attack to the wheel is likely is if the air in it has a very high water content to assist the oxygen in attacking the wheel. In 15+ years of fitting tyres I have never seen a wheel or tyre that has suffered in such a way: but the exposed outer part of the tyre or the external edge rim-to-bead seat may often show degradration. The only advantage of Nitrogen is that it would be dried to remove any surplus water vapour.

Some tyres used in big earth moving equipment are filled with Nitrogen but these tyres are very heavily constructed and so may be remoulded several times in their life span over several years: therefore anything which helps to keep the tyre carcass in good condition is worthwhile given that the tyres can cost several thousand pounds each, and are inflated to much higher pressures than passenger car tyres.

Nitrogen is more stable at holding it’s pressure when the tyre goes through the cycle of cold to hot and back again in normal use. WRONG Oxygen and Nitrogen and Air all respond in the same way to temperature changes as the tyre heats up and cools down: they all have the same rate of pressure change for an equal amount of temperature change.

Again the only exception would be if very wet air was used to fill the tyre: if the water content was so high that in cold temperatures there was liquid water in the tyre which could turn to water vapour when the tyre heated up. This would cause an uneven pressure gradient in respect of temperature: effectively a very small amount of water would turn into a large amount of steam within the tyre casing. In normal use (at least in my tyre depots) the air-lines are fitted with water traps to remove excess moisture from the compressed air.

Nitrogen is not a fire risk CORRECT It is a requirement to use Nitrogen (or another inert gas) with less than 5% Oxygen content for aircraft tyres. For aircraft where the tyres in normal flying use are stowed within the wings or fuselage it is obviously desireable to have a tyre NOT filled with pressurised air should a fire occur. The amount of water vapour and carbon dioxide in the tyre should also be minimal or it could condense at high altitude and freeze to ice which would give an unbalanced situation when landing. The fire risk benefits of inert gas filling also apply in other safety critical situations, but have no real advantage for private motoring.
Nitrogen is used in Formula 1 and other race cars. CORRECT Nitrogen is used because it is easier and more reliable than using an air compressor. The cylinders of Nitrogen are also used to power the impact wrenches for wheel changing.
Car manufacturers still use compressed air when making new cars CORRECT Vauxhall do not disapprove of Nitrogen but do not seriously endorse any of the claimed benefits.

Similarly the AA do not endorse Nitrogen filling for Road Cars