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The much-touted advice to use nitrogen in your tyres as opposed to normal air has been around for many years and it’s time to have a closer look at the subject, says Mic van Zyl.
According to some tyre centres, nitrogen offers improvements in tyre life, steering, braking, grip, economy, reduced pressure loss over time, reduced tyre failures, lower temperatures, and improved performance and safety for you and your vehicle. You would apparently be an idiot to use normal air in your new, expensive tyres.
I was sitting in a wheel-and-tyre centre recently having the tyres on my Land Cruiser rotated. I am fortunate not to have to pay for the tyres on my company vehicle. Notwithstanding this fact, I am meticulous when it comes to my tyres, suspension and brakes. They are my big three safety critical items. I rotate religiously and I constantly check my tyre pressure monitor when driving.
My eyes literally watered when I heard a salesman quote a customer for a new set of tyres for her performance SUV. He then proceeded to offer her nitrogen at R38 per tyre. His sales pitch for the nitrogen was truly mesmerising. He managed to convince the lady that the additional R190 for the nitrogen in her five tyres would save her thousands in the long run. This, of course, had me sit up and ponder the subject.
So, what is the deal with nitrogen in your tyres? Many of these fantastic claims are somewhat true. When we look at them scientifically, however, the advantages are minor. Atmospheric air is already 79% nitrogen. The nitrogen pumped into your tyres at the tyre centre is 95% pure. The best improvement you could thus enjoy by using nitrogen would be 16% at best.
It is true that tyres running with pure (95%) nitrogen will run cooler than with normal air. But by how much? The specific heat of normal air at around 30% is 1 joules per gramme kelvin (J/g K) and for nitrogen it is 1,04. A difference of 4%. Take a tyre inflated with air at a cold temperature of 20 °C and a pressure of 2 bar. After some driving and an operational temperature of 40 °C, the pressure would have increased to 2,36 bar.
The same tyre filled with nitrogen starting at 20 °C and ending at 38,4 °C (allowing for the 4% difference in specific heat) would end up with a pressure of 2,35 bar. Hardly significant.
Another claim is that the lack of oxygen in the nitrogen will prevent the oxidation of the inner surface of the tyre. Another true fact that has very little real-world significance. Bear in mind that the outer surface of the tyre is also exposed to oxygen along with a host of added harsh elements and we just do not see tyres falling apart due to the rubber oxidising.
We replace our tyres due to wear or age long before this becomes an issue. All the claims regarding steering, braking, grip, economy and improved performance are pure nonsense. These characteristics are all a function of the tyre tread, road condition, tyre pressure and temperature.
The tyre couldn’t care less what type of gas is exerting the required pressure on its inner surface. If the pressure is correct, it doesn’t matter.
The prize for the most ridiculous nitrogen claim has to be the fact that nitrogen permeates or leaks through the rubber of the tyre at a much slower rate than air. Absolutely true. The size of an oxygen molecule is around 0,299 nanometre and nitrogen is 0,305 nanometre – a difference of under 2%.
A controlled test conducted by the Organisation for Consumer Reports in the USA found that the loss in pressure of tyres filled with nitrogen was only 1,264 kPa (0,0126 bar) per week vs 2,010 kPa (0,0201 bar) for the same tyre filled with air. Again, negligible. The most disturbing aspect is the fact that people may end up checking their tyre pressures less frequently when using nitrogen.
Tyre failures and blow-outs due to incorrect pressures are a massive contributor to road fatalities. Advocating the use of a product that would cause motorists to neglect checking their tyre pressures regularly is grossly irresponsible. In my view, the advantages are just not worth the effort or money.
