Have you had your tyres changed recently, and were you asked if you wanted them filled with nitrogen? Here’s why it’s a waste of money.

Tyre companies offering to fill your tyres with nitrogen has been a ‘thing’ for the last couple of years. And the argument, they’ll make, is good…on the surface.

Race cars run nitrogen in their tyres and so do aeroplanes because it’s more stable in high-pressure situations and so, I’ve been told by at least two tyre shops, everyone should be filling their car tyres. And it’ll only cost a couple of bucks per tyre. What’s to lose? Well, money, for a start.

There are those on the Interweb who’ve bought into the nitrogen in car tyres argument hook, line and puff of nitrogen. They’ll say that nitrogen is super stable and so will reduce natural air loss through oxidation. And there’s a grain of truth in that so, let’s bring a little science into the debate.

We all know that air is made of 78% nitrogen, 21% oxygen and 1% other gasses. However, the nitrogen you’ll need to pay for to have pumped into your vehicle’s tyres is generally a mixture of no less than 90% nitrogen and no more than 10% oxygen. Of course, it could be a lot more nitrogen but it can’t be less than the 90% to be considered pure nitrogen.

There really aren’t many studies into running nitrogen in vehicle tyres, yet that hasn’t stopped tyre shops trying to peddle the stuff. One study we found by the US National Highway Traffic Safety Administration (NHTSA) was conducted in 2009 and saw researchers run a 90-day static lab test, which also included oven testing to simulate road running and three years of life. Tyres studied were a mix of general car tyres and light truck tyres.

The study found that after 90-days the 99% (one percent oxygen) pure-nitrogen-filled tyres lost around 1.39% of pressure/month while the air-filled tyres lost double that at 2.13%/month. However, if after the first 90 days the air-filled tyre was topped up with air its subsequent 90-day pressure drop pressure would fall to 1.59%. How’s that argument looking now?!

Researchers concluded that while oxygen in the mixture was oxidising in the tyre and being lost, the original nitrogen content remained static and actually increased once the tyre was topped up. In fact the amount of nitrogen in the tyre had risen from 70% to 85% once the tyre had been topped up.

The results of the three-year study by the NHTSA revealed that there was a 17% advantage gained by filling vehicle tyres with pure nitrogen compared to air. But that was determined based on testing at 90-day intervals (no tyre checks in that period). So, check your tyres every week or so and top them up as required and that ‘left-alone’ advantage of nitrogen will vanish.

And, to bust another myth, the NHTSA study found that filling vehicle tyres with nitrogen compared with air alone had no effect on the rolling resistance of the tyre. Indeed, after 90 days of no inflation pressure maintenance resulted in air-filled tyres experiencing a 1.5% reduction in rolling resistance. Or, as my old man might say, bugger all.

And it was the same with the alleged degrading effect of oxygen on vehicle tyres. Yes, if you’re going with an oxygen-rich mix of 50:50 then you’ll have all sorts of problems but given the air being pumped in via a compressor is a mix of around, at least, 70% nitrogen then you won’t have any problems. And that’s not just me saying it. According to the NHTSA study, its 90-day static test and accelerated oven ageing showed no difference (in tyre/rubber degradation) between air-filled or nitrogen-filled tyres. 

So, the moral to the story here is, don’t waste your money on filling your vehicle tyres with nitrogen, just perform a regular five-minute check on your tyres and keep them topped up at the manufacturer’s recommended pressure and you’ll be fine. And you’ll save yourself a fistful of dollars into the bargain.

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