buddy427

Wondering if any out there have had any experience with Nitrogen or Carbon Dioxide in their tires?

I just had a guy come over to my house and he had a very slick Nitrogen setup in a small trailer. He did my race tires and car tires plus put 90lbs in my (formerly air) tank!

Then I talked with a friend who runs A-Mod and thought he ran nitrogen but he tells me he does Carbon Dioxide. He told me to do a Yahoo search on powertank. That's interesting reading but will Carbon Dioxide expansion due to heat compete with Nitrogen?

I took my car out today and kept the tire pressure display on. Got the tires good and hot. Pressure varied only 1lb from cold. Left the car in the sun for over an hour. Checked the tp's again and still no change.
Impressive.

Bob

rgs

Both CO2 and Nitrogen respond to the Idea Gas Law PV=nRT. Both will respond to heat the same. The difference is reactivity. Nitrogen is less reactive to rubber and will age it slower than CO2, but on a tire with a relatively short life span, it really isn't an issue.

Sidney004

The pressure rise with air is probably due to its saturation with water. Most air tanks (mine for instance) have pools of water inside. Nitrogen that is produced will be very dry.

John Shiels

Welding supply will rent you a big tank for 25 bucks per year. Then you need to get some hose and a gauge. I have bought a small tank to take to the track to add some or fill a tires if need be. Never did it because of DOT regulations.

buddy427

So, if I did 1 tire with Nitrogen and the other with CO2, then drove the car for say 15 minutes at highway speeds, then stopped and checked the tire pressures(started with the same in each tire), that both tires would show the same increase in tire pressure?

Bob

aggie_corvette

Its not he N2 or Co2 that is causing the pressure rise. Its the water or humidity of the "air" that is expanding as it heats. They use nitrogen mostly for the dry element, but co2 will work the same and might be cheaper.

You can get the same effect if you just super dry the "air" using welding type air driers/cleaners. You have to run two canisters, one to remove the compressor oils and another to dry the air (chemically with a replacable honeycomb insert, think Britta filter). The driers fit inline with the tank.

No matter what you do, you need to cycle the air (empty then fill) atleast twice to remove the "humid" air.

95jersey

Usually a bleed between sessions works....now I got to pay for air in my tires?!?!

Don Keefhardt

Every gas...EVERY gas...will expand as it gets warmer. Some already cited the 'Ideal Gas Law' - PV=nRT. Basically, it says that pressure, volume and temperature are all inter-related.

If temperature goes up but volume can't change, the pressure will rise (think "inside a tire"). Nitrogen, Air, Argon, Carbon Dioxide...they all do this. The major variability is water content. If you've got water in your tires, as it gets hot and goes from liquid to vapor stage (due to temperature), the pressure will rise differently inside the tire than with a 'dry' gas. Dry nitrogen is VERY cheap, and very inert. 'Inert' means that it's not an oxidizer, so it won't feed a fire. Race organizations restrict pit lane gases to nitrogen, since a burned-thru pressure line won't add oxidizers to a fire, also why pit lane fuel transfer pumps are pneumatically-powered (like CART/Champcar). I carry a tank of nitrogen in the race trailer, because it's CHEAP and I don't have to start a compressor to get it...all I have to do is open a valve.

The idea that nitrogen will get you better mileage and longer tire life and freshen your breath and neuter your dog is pure marketing BS. A 'properly inflated tire' will get you those things (minus the breath and dog thing), regardless of the gas inside it. Please don't try and make an arguement about molecular size and slower leaks...go back to chemistry class and PAY ATTENTION.

davidfarmer

Any bottled, ideal gas is fine. Air works fine if you can find DRY air.

And to screw things up even more, pure Nitrogen will only give limited success. Most tire shops have air compressors that are absolutely FULL of water, plus they use water/soap to lubricate the bead when they mount your tires. Unless you repeatedly VACUUM your tires, refilling with Nitrogen in between, you will never get the moisture out.

Water vapor is the enemy, not the air.

Most racers use Nitrogen, as their are suppliers that bring truck loads of it to the track (for rental). Fill the tires, drain them, re-fill at least once more, then race. It will knock a few psi off of the pressure gain.

ghoffman

Thank you! I hate arguing abut things that are axioms.
The only reason I use N2 for my shocks and tires is it is cheaper than the Argon I use in my TIG and I don't have to bring a compressor and generator in my trailer.

varkwso

Anybody who has been in an altitude chamber can easily relate to the expansion differences between a dry and wet gas.....

We use argon and nitrogen in hot cells to control moisture (and to inert!) also.....

robvuk

Although I have never had any direct experience with nitrogen, I am somewhat doubtful about the affect of moisture as well. Any liquid that converts to a gas at a given temperature will have a HUGE expansion ratio. That's called the boiling point. Having said that, water and water vapor suspended in air will remain a liquid until the boiling point of 212F or in the case of a pressurized tire much higher than that yet. So if there is any truth to the affect of water causing higher pressure gains, it would only be in racecars that heat up the air in the wheels to a point above 250-300 degrees or so. I doubt that any street car has tire air temps that high. Up until the temp of the water reaches its pressurized boiling point, it will basically remain the same volume of room temperature water. Any thoughts?

yellow01

What about Hydrogen? I mean, it's much lighter, so will reduce rotating mass, and it worked for the Hinden...oh wait, nevermind

varkwso

It is water vapor (think humidity) that is the problem - not really liquid water - I think it is called Boyle's Law. Boiling not required....

robvuk

Boyle'ls Law is in regards to pressure and volume. P1V1=P2V2. Just an example of the proportionality between pressure and volume. Humidity is water vapor suspended in the air like the clouds in the sky, which comes from evaporation of water as opposed to boiling. But the temperature and pressure still have to be high temp and low pressure for much evaporation to occur. (eg. muggy days when hot) High temp is there but pressure is too high for much evaporation. So if humid air is put in under enough pressure, the humidity will actually condense back to water. You may be on to something here, I'm just not sure if the conditions would actually do what people claim. Surely there are people on this forum who are much more competent than I am on their chemistry.

yellow01

ChemE degree from UT (the real UT, Texas ) and you guys got it.

It always makes me laugh when I see the nitrogen discussion, and I always make private bets with myself to see how long it takes for someone to post pv=nRT

Water vapor has interesting properties... there are books dedicated to Steam Tables which characterize pressure/temp/saturation points etc. of steam since it is so typically used in plants for a variety of purposes. This situation is slightly different, but basically the same.

I haven't used steam tables since school because I work in a different field... so it's been a looooooooong time

robvuk

I'm glad you are amused. So you've been watching this thread and just let me strangle myself? And then you didn't post an opinion?? Or a verdict? Please tell us, inquiring minds want to know once and for all.

Am I just blowing hot (steamy) air?

yellow01

No, I agree with you

Bottom line is the water in the tire is what causes the significant difference in expansion between "air" and nitrogen in the tires. Hell, "air" is 79% Nitrogen If you filled your tire with N2 with 60% RH you'd see a big difference between hot and cold pressures too.

From the ideal gas law, increase in pressure is linear with increase in temperature. Increase in vapor pressure is non-linear with temperature, increasing sharply between room temp (30C) and above. Water vapor can also absorb and retain significantly more energy, meaning tires run hotter, exacerbating the above. So it is the water vapor causing the departure from ideality.

Otherwise, N2 or Air (N2/O2) would be the same.

As far as permeability, I've never seen anything other than anectode after multiple attempts over the years to actually find diffusion rates.

varkwso

I was looking for the reference to the Ideal Gas Law (we use in hydrolysis calcs - among others) and mixed gas (i.e., ambient) partial pressures. Way too much effort for a Friday evening...

The most painful part was agreeing with a UT ChemE.....

yellow01

Aggie?! Sooner?!