The idea of inflating car and motorbike tyres with Nitrogen has been around for a while now, with advertisements suggesting it’s safer and enhances performance. Is it true though and, if it is, should we be filling our mountain bike tyres with this (relatively) expensive invisible stuff?
Nitrogen versus Air – what’s the difference?
There are two main differences between Nitrogen and air and it’s these differences that form the basis of the arguments for using Nitrogen to inflate tyres.
Whether we’re breathing it or pumping it into tyres, Nitrogen makes up 78% of air anyway so the arguments are around the remaining 22% of air constituents. The remaining 22% of air is made up of:
- Oxygen – which accounts for 21 %.
- Things like Argon, Carbon Dioxide and crucially, when it comes to this question, water vapour – all of which account for 1%.
So lets look at these two differences…….
Nitrogen molecules are bigger than Oxygen molecules
One of the arguments behind Nitrogen filled tyres is that they stay inflated for longer as the smaller Oxygen molecules can penetrate and escape from rubber tyres more easily.
This statement is 100% true but, while it is true, how often do you find yourself pumping up your car and bike tyres? Not that often is it.
When comparing the cost and inconvenience of filling tyres with Nitrogen against the cost of a bike pump this question becomes a no brainer really. It’s not a big enough issue to be worth consideration, particularly when you start considering things like inner tube punctures and burping tubeless tyres.
Nitrogen is a dry gas but air has water vapour in it
Another 100% true statement and the main argument for using Nitrogen in tyres.
Tyres ‘grip’ the ground as a result of friction between the tyres and the ground. This friction generates a release of energy as heat (with heat also generated by the release of the compression of the tyre against the ground as the tyre rolls).
Under hard tyre use, the temperature inside a tyre can start to build. The net effect of this is that the water vapour in the air inside the tyre expands resulting in the tyre becoming over inflated and a loss of grip due to a reduced contact patch between the tyre and the ground.
The issue with this argument, when it comes to mountain biking, is that mountain bike tyres are never under sufficient stress to become hot. You can see smoke coming from car and motorbike tyres or smell ‘burning rubber’ at race tracks e.t.c but the loads mountain bike tyres come under aren’t high enough to significantly heat the tyre to the point you’ll experience a discernible difference in performance.
So in conclusion, while the idea of inflating mountain bike tyres with Nitrogen might appeal to some people, the reality is there’s no real justification for it.
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