The subject of using nitrogen to inflate car tyres has received considerable publicity over the past few years; particularly since some tyre retailers have begun promoting its supposed benefits.
It is well known that 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.
So what is nitrogen?
Nitrogen is a colourless, odourless, tasteless, and non-toxic gas that forms about 78% of the Earth's atmosphere. The benefits claimed for using nitrogen over compressed air for inflating tyres are that it:
Reduces the tyre's running temperature
Improves the ride quality
Increases tyre life
Keeps tyre pressures more constant
Slows the rate of pressure loss
Doesn't react with the tyre and rim materials
The following is a discussion of these points.
Reduces the tyre's running temperature
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.
Nitrogen improves ride quality
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.
Nitrogen increases tyre life
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 questionable.
Reduced pressure build up
The reason that tyre pressures should only be checked when cold is that the tyre’s inflation pressure increases in relation to 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.
Pressure loss is slower with nitrogen than with air
Tyre liners and tubes are to some degree porous, and as a result air will eventually leach out. Hence the need to regularly check tyre pressures. Nitrogen, due to its chemical structure, is slower to leak out than compressed air. Therefore the pressure loss is slower. However that doesn't mean that regular pressure checks can be neglected as there is still the possibility of a puncture or some other form of slow leak.
Nitrogen doesn't react with the metal wheel rim or the tyre materials
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 (though not a member of the 'noble' gas family) and because it is dry, this problem is, in theory, eliminated. However, unless the tyre is evacuated (i.e. the air is removed) before the nitrogen is added, there will still be some air and possibly moisture in the tyre.
Disadvantages of nitrogen
Nitrogen also has a few disadvantages that should be taken into account. These include:
The typical charge for nitrogen is between $5 and $10 per tyre for a passenger car.
Once your tyres are filled with nitrogen it's important that only nitrogen is used for top up purposes. Adding normal compressed air will negate any benefits of the nitrogen.
If you are in an area where nitrogen is not available and top up is necessary, normal compressed air will have to be added. If you wish to reinflate with nitrogen later you will need to locate a nitrogen outlet, deflate the tyre and then reinflate it with nitrogen.
Nitrogen simply isn't readily available everywhere. It's generally restricted to specialist tyre dealers.
A few things to consider
The earth's atmosphere is comprised of roughly 78% nitrogen and 21% oxygen with a few trace gasses mixed in, so when you fill your tyres with compressed air, you are getting about 78% nitrogen anyway.
Not all aircraft use nitrogen in their tyres. In fact generally only larger aircraft with high altitude capability and high landing and take off speeds and high loads use it. The reason given by the Civil Aviation Safety Authority to support its use is that nitrogen, being a relatively inert gas, reduces the risk of high altitude tyre explosions that could damage or destroy an aircraft. Obviously this is hardly a consideration for the average passenger car operator.
Nitrogen is also sometimes used in the tyres of vehicles that operate in potentially hazardous areas, such as mines, to reduce the risk of fire. It is also commonly used in off-highway vehicles where the tyres operate at their maximum load and are highly stressed.
A number of tyre manufacturers have produced position papers on nitrogen, as has the Australian Tyre Manufacturers Association. Some tyre manufacturers have declined to comment. Most have indicated that tyre warranties will not be affected by the use of nitrogen.
While using nitrogen in passenger car tyres may produce some benefits in some applications, it is questionable if the average motorist will derive any measurable benefit from its use.
Using nitrogen does not remove or reduce the need to check tyre pressures as the risk of a puncture or a slow leak is not altered.
Many of the benefits claimed of nitrogen could be achieved by using dry compressed air from a properly designed and maintained compressed air system.
Nitrogen cannot replace regular maintenance. Regardless of what inflation gas is used, maximum tyre life will only be achieved if the vehicle and tyres are properly maintained. That means regular checking of tyre pressures, wheel balance and alignment.