Nitrogen in tyres/tires

[John Clarke]

Hi All
We are just having the new Vredestein Sprint Classics fitted and they were inflated with Nitrogen.
Never had this done before, I believe race cars use this, but is there any advantage on a 356 Street car? They are tubeless and are fitted to 5 Spoke EMPI Alloys.
Cheers Jay

[Glen Hamner, Jr]

John,

A no brainer enhancement. All of our vehicles are filled with nitrogen. Air pressure will not change with the seasons. Be sure to use a supplier who will adjust your nitrogen fill whenever it moves out of specs, for free, after the initial filling. My supplier is easy to work with and always has someone ready to top things off. No, it takes no time and really last a long time. Been using nitrogen for the past 10 years.

[Matthew Devereux]

Air is 78% nitrogen

[Glen Hamner, Jr]

How right your are, and that 22% left over is what expands and contract with temperature. Soooooo, play with the air and your air gauge, or, use nitrogen and let it be most of the year. I spent $5 per tire for Nitrogen, never think about it except when it's time to change the oil. The service center takes care of any change, which is almost never. All in all, an interesting exercise.

[Eric McKinley]

John,

I watched a show in the recent past.
It focuses on companies that supply tyres and charge for filling them with nitrogen.
A study was conducted across the uk in relation to this.
I cannot remember the statistics however it was shown that only a few had actually been filled with nitrogen.
Worth keeping in mind.

[Wil Mittelbach]

Nitrogen gas pressure in a fixed volume will vary as a function of temperature, as does oxygen and air.
A pure nitrogen tire fill, less air's oxygen content, will curtail internal tire rubber oxidation relative to the tire's external surface in an air environment.

[Sam Good]

The thermal expansion coefficient of nitrogen isn't all that much different from that of oxygen, CO2, or plain old air.

Provided, of course, there isn't much moisture in the air. Water vapor has a much steeper expansion curve. So there'll be a difference between humid ambient air, and pure dry nitrogen. The water vapor is the reason racers prefer nitrogen. (However, I work in a lab and let's just say our nitrogen vendor has gotten in trouble for excessive moisture in their product. It happens. No guarantees that you truly get what you're buying.)

One key difference for us in our old cars is that nitrogen is inert. Rims can't rust and tires can't rot in the absence of oxygen. However, your tires and rims will still be exposed to oxygen on the outside, so one might wonder what the point is. But trying to slow down the aging process on the inside of the casing (where you can't see it) is not unreasonable.

The difference in ability to hold pressure will be real but negligible. Oxygen is highly reactive and can permeate into the rubber, but it's only about 17% of the air so you won't see huge pressure drops due to gradual O2 loss.

Jet airliners use nitrogen in their tires mainly because oxygen is a key component in fires. Just a little extra margin of safety, to keep the tires from catching fire in the event of an unusually bad emergency landing with high speeds and hot brakes. Doesn't apply to us. If you find yourself driving fast enough to catch your tires on fire, you should stop doing that.

There's no harm in running nitrogen, but the benefit is pretty darn small. Then again, the price tag is small too. There isn't a wrong answer; air is perfectly fine and nitrogen is infinitesimally better for a miniscule amount of money. I'd happily say 'yes' to nitrogen if it were offered cheaply at tire install time, but I wouldn't go out of my way to avoid topping it up with ordinary air. We aren't racing, we aren't landing jet airplanes, and it just isn't that big a deal.

[Mike Ruddy]

I understand Ferrari use CO2 in their tyres. Personally I prefer helium as it reduces the unsprung weight at each corner and gives a higher pitch tyre squeal which impresses girls.

Here's Tiff Needell investigating Nitrogen on 5th Gear.

https://www.youtube.com/watch?v=knHeUF9JLzg

[John Clarke]

Hi All
While down at the tyre/tire fitters today, I asked more about the 'Nitrogen' that they use and was shown the unit that removes All of the moisture content from the air prior to use. But does this make it pure Nitrogen? Matthew mentioned that Air is 78% Nitrogen but what about that remaining 22% of 'Dehumidified' Air ?
Jay

[Glen Hamner, Jr]

Middle of the road summary by Tire Rack.

http://www.tirerack.com/tires/tiretech/ ... techid=191

[Vic Skirmants]

I carry a nitrogen tank in the race car trailer. It's for convenience; I don't have to run to the tire mounters to fill the air bottle all the time.
Also, a long time ago I found my tires acting strangely regarding pressure build up. I went to the mounters and asked about their air compressor; when was it last drained? They opened the valve on the bottom and about a quart of water came out.

[Jon Schmid]

Funny you should mention that, Vic. I always drain my compressor when I'm done using it and I always try to find a low humidity day (common out here) to air up the compressor and check/refill my tires.

[Matthew Devereux]

If the air has time to sit in the tank and cool a lot of the moisture will condense out. I bought an old refrigerated air dryer as my plasma cutter requires dry air. It will bring the dew point down to 3 C. The other alternative is to use a desiccant type air dryer. These aren't very expensive.

[Jim Alton]

Oxygen, Nitrogen, Carbon Dioxide, Helium, and Argon all obey the ideal gas law: PV - nRT

where (from Wikipedia):

• P is the pressure of the gas
  V is the volume of the gas
  n is the amount of substance of gas (in moles)
  R is the ideal, or universal, gas constant, equal to the product of the Boltzmann constant and the Avogadro constant.
  T is the temperature of the gas

I frankly don't know the rationale for choosing CO₂ over N₂ or vice versa. Pure oxygen's very reactive and would probably cause the tires to decay--assuming it didn't ignite grease. Helium and argon probably cost too much and the tire might be permeable to these.

Water--on the other hand--can exist as a solid, a liquid, or a gas at temperatures car tires can encounter. Those phase changes can cause big pressure changes as Vic noted.

CO₂ or N₂ from a cylinder should be really, really free of water. One can also buy compressors that deliver dry air (but not cheaply).

Personally, I think checking tire pressures every 4 weeks and adding air from my lowly Craftsman air compressor is better for street use than going to CostCo for nitrogen every six months.

[Emil Wojcik]

I'm sure my tires are all full of water. I just don't care.