Compressed Air vs. Nitrogen

Is there any advantage to using nitrogen instead of compressed air in tires?

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.

First of all, air is 78 % nitrogen, just under 21 % oxygen; the rest is water vapour, CO2 and small concentrations of noble gases such as neon and argon.

There are several compelling reasons to use pure nitrogen in tires.

Nitrogen is less likely to migrate through tire rubber than oxygen, which means your tire pressures will remain more stable over the long term.

Humidity (water) is a bad thing to have inside a tire. Water, present as a vapour or even as a liquid in a tire, causes more of a pressure change with temperature swings than dry air does. It also promotes corrosion of the steel or aluminium rim. How is water relevant to a nitrogen discussion? Any system that delivers pure nitrogen is also going to deliver dry nitrogen. Filling tires with nitrogen involves filling and purging several times in succession, consecutively diluting the concentration of oxygen in the tire. This will also remove any water. (If you depress the tires chuck valve with your thumbnail to vent some air and your thumb gets wet, there’s still water in the line)

Filling your tires with nitrogen mainly does two things: it eliminates moisture, and it replaces skinny oxygen molecules with fat nitrogen molecules, reducing the rate at which compressed gas diffuses through porous tire walls. This means, theoretically at least, that a tire filled with nitrogen retains optimal pressure longer, leading to more uniform tire wear and better gas mileage. The commonly quoted figure is that tires inflated to 32 psi get 3 percent better mileage than at 24 psi.

It’s quite simple, but time-consuming for a tire technician to fill and bleed tires. Most shops use a machine that not only generates almost pure nitrogen by straining the oxygen out of shop-compressed air, but will also automatically go through several purge cycles unattended.

So, to get to the point, with nitrogen your tire pressures will remain more constant, saving you a small amount in fuel and tire-maintenance costs. There will be less moisture inside your tires, meaning less corrosion on your wheels.

You won’t be able to feel any difference in the ride, handling or braking, unless your tire pressures were seriously out of spec and changing to nitrogen brought them back to the proper numbers.

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. Also regular checking of tyre pressures, wheel balance and alignment is still of importance.

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Lover of Muscle Cars, Zombies & Famous Movie Monsters. Busy restoring a ’70 Ford Fairmont. Collector of HotWheels. Firm believer of "Anything that gets your blood racing is probably worth doing".

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