Nitrogen gas has been used to inflate the tyres of racing cars, aircraft, and heavy commercial vehicles for some time. However, it is only relatively recently that it has come into use in normal passenger cars.
Nitrogen is a colourless, odourless, tasteless, and non-toxic gas that forms about 78% of the Earth's atmosphere. The claimed benefits of nitrogen over compressed air for inflating tyres are that it:
While there is some truth in this statement, the difference relates to the moisture content of the inflation gas rather than the use of nitrogen per se. In fact, dry compressed air will also produce a cooler running tyre. It's also only likely to be of benefit in cases where the tyres are operating at or near their maximum load and/or speed capacities.
No explanation has been offered as to why this should be the case. There should be no significant difference in the way air and nitrogen behave at normal tyre operating pressures and temperatures.
A tyre's operating temperature plays a part in how rapidly it will wear. A reduction in temperature at high speeds and loads will be beneficial. However, claims by some supporters that nitrogen will double tyre life are highly questionable.
A tyre’s inflation pressure increases with temperature. Nitrogen is claimed to provide a more stable pressure range in relation to tyre temperature. However, once again the moisture content of the inflation gas plays a bigger part than the gas itself. Any benefits are likely to be achieved only under heavy load and/or high-speed conditions.
Tyre liners and tubes are to some degree porous, and pressure will eventually drop. Hence the need to regularly check tyre pressures. Nitrogen, due to its chemical structure, is slightly slower to leak out than compressed air. Therefore, the pressure loss will be slightly slower. However, that doesn't mean that regular pressure checks can be neglected as there is still the possibility of a slow leak.
Probably true. The presence of oxygen and moisture inside the tyre can cause oxidisation (rust) of the metal components. There is also a suggestion that air reacts with the rubber of the tyre itself, however it is not clear if this is detrimental or in any way reduces the life of the average car tyre. Because nitrogen is a relatively inert gas and because it is dry, this problem is, in theory, eliminated. However, unless the air in the tyre is removed before the nitrogen is added, there will still be some air and possibly moisture in the tyre.