The reasons for filling your tyres with nitrogen are hot air.

The next time you buy new tyres, you may be asked by the tyre shop if you want them filled with nitrogen. You'll be told nitrogen:

• leaks more slowly from the tyre than compressed air, so you'll get longer tyre life and better fuel economy because your tyres are less likely to be under-inflated
• gives a lower tyre temperature, reducing  tyre wear
• contains less moisture than compressed air and so your wheel rims are less likely to rust.

Then there’s saving the planet:  a study by Bridgestone (a tyre company) found almost 94 percent of cars in Europe had under-inflated tyres – wasting an extra 8.1 billion litres of fuel every year plus the resulting pollution.

So at a cost of around $5 per filled tyre, nitrogen doesn't sound too bad.

Checking the claims

Unfortunately, these claims don’t stack up.  Consumer Reports in the US conducted a year-long trial with nitrogen and found it only marginally reduced tyre-pressure loss. Even a nitrogen-filled tyre loses pressure, which means topping it up periodically – but topping it up with air will undo the "benefits" of the nitrogen already in there. So you'll need to pay for nitrogen top-ups from the tyre shop.

That nitrogen cools your tyres and extends tread-life is also tricky. Cooling down a tyre may give a little more tread life but can also reduce grip – not pleasant to discover when driving on a cold, wet road. Tread is not the only thing holding you on a wet road – the compound of the tyre, inflation pressure and heat in the tyre also play crucial roles.

The argument that nitrogen reduces moisture in the tyre is irrelevant as it’s extremely unlikely that your tyres or rims will fail because of moisture inside a tyre.

We say

• Nitrogen provides some cost-benefit to heavy commercial vehicles and helps stop Formula 1 tyres from overheating. But for the average motorist it provides virtually no benefit, costs money, and may reduce safety rather than improve it. It’s a good way for tyre companies to make a little extra money though.
• Regularly checking your tyre pressures and being gentle with your right foot are our advice for improving tyre life and fuel economy.
   

More from consumer.org.nz

• Car tyres - test results for over 40 tyres, plus tyre-care tips

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