CO2 in my tires

[mingoglia]

My wife is heading off on a small road trip (650 miles) so this morning I checked the tires. Since it had been a month since I checked the pressure and we've had wild temperature fluctuations, I wasn't surprised to see the front at 38 and the rear at 36. I keep them at 42/40, so I reached for the tire chuck to top 'em off.

It was early in the morning and I didn't want to wake up the kids with my big shop compressor kicking on so I decided to use my 20lb CO2 tank to top off the pressure. I'm beginning to use my CO2 tank more and more over my compressor to fill up tires, run air tools, etc. One tank is the equivalent to around 650 gallons of air (if my memory serves me) and with a 150psi regulator, it's regulated pressure is the same as my big compressor.... not to mention it's incredibly portable.

Here's my question. Just like nitrogen has some benefits with air seepage, are there any DISadvantages to using CO2 instead of "plain 'ol" air? I do know the temperature is much much colder from the process of converting from a liquid to a gas so that has the potential to affect things. In contrast my shop air would be very very hot. Not only is it hot right after being compressed (obviously) but the air in my tank is sitting in my 120 degree garage (I live in AZ). The air is also very damp from the compressing process...I'd imagine the Co2 is pretty dry.

I know it may sound like using CO2 isn't ideal due to environmental concerns. My OPINION is the process of creating CO2 pulls CO2 out of the air, converts it to a liquid, then ultimately makes it into my tank. In my eyes this means that it's somewhat carbon neutral? Yes, there's of course fossil fuel being used at some point for the process of creating the liquid CO2, but then again there's electricity used to compress the air for my compressor as well. If I'm completely wrong in my thought process, call me out on it as I'm not claiming to be an expert on this process.

So anyway, figured there's a lot of highly educated folks on this forum... so whatcha think about my tire question? Do you think the CO2 is going to act much different throughout the temperature range of the tire? Do you think the pressure difference when driving at different altitudes will vary more or less? In other words, my wife during the trip will be traveling from approximately 1,000' above sea level to over 8,000' above seal level. How will running CO2 affect tire pressure during this trip?

Mike

[carz89]

You probably remember the ideal gas law from chemistry class, PV=nRT. If you understand this equation, then you'll realize that the heatup/cooldown of tires due to usage or environmental temperatures has no relation whatsoever to the type of gas inside your tire. Changes in pressure of a gas in an enclosed system are not affected by type of gas.

Lots of discussion out there on the exaggerated benefits of using pure N2 gas in automobile tires. Google it. Here's one good discussion: The force that through...: Nitrogen for tires?

Any touted difference in diffusion rates is unsubstantiated. N2 and O2 molecules are almost the same size, and air is 80% N2 anyway. The only plausible benefit to using pure N2 is that you might reduce the oxidation of the rubber inside the tire. But, I would think that you would wear out the tire tread long before rubber oxidation would become a problem, unless you are a car collector and wish to keep your prized possession for decades.

Personally, I have better things to waste my money on than $20 to fill up 4 tires with N2. What a scam!

As far as CO2, probably the same arguments apply. I haven't researched the diffusion rates and corrosivity of CO2, but I am skeptical. Again, the type of gas you use will have no bearing on the daily expansion and contraction of your tire. However, if you do choose to use CO2, you need to be aware that CO2 will combine with water to form carbonic acid, which is much more corrosive than the O2 within the air. Thus, you should try to use extremely dry CO2, and to displace most of the moisture (in the air originally in the tire) by filling/exhausting each tire several times.

[qbee42]

No difference between N2, CO2, and plain old air. They all work equally well, assuming you get the water vapor out of them. CO2 becomes non-ideal at higher pressures and lower temperatures, but that happens well out of the range of operation for normal car tires.

Tom

[Shawn Clark]

CO2 is denser (higher MW) so you will have a slight increase in unsprung weight on each corner. I haven't tried to calculate it but expect it will be negligible.

I doubt the higher partial pressure of CO2 would have any reaction effects with the alloys or rubber. This is the area of concern I would have. Some chemists would be more qualified to evaluate the materials (including the sensors) and the combination of water, CO2, and N2. CO2 itself should not condense/freeze at these temperatures and pressures.

If there is moisture (condensate) in the tire the CO2 will more readily dissolve in it than N2 or O2 if I'm not mistaken. If this is correct then there will be more pressure loss during colder operation.

[ctbering]

Originally Posted by carz89

You probably remember the ideal gas law from chemistry class, PV=nRT. If you understand this equation, then you'll realize that the heatup/cooldown of tires due to usage or environmental temperatures has no relation whatsoever to the type of gas inside your tire. Changes in pressure of a gas in an enclosed system are not affected by type of gas.

Lots of discussion out there on the exaggerated benefits of using pure N2 gas in automobile tires. Google it. Here's one good discussion: The force that through...: Nitrogen for tires?

Any touted difference in diffusion rates is unsubstantiated. N2 and O2 molecules are almost the same size, and air is 80% N2 anyway. The only plausible benefit to using pure N2 is that you might reduce the oxidation of the rubber inside the tire. But, I would think that you would wear out the tire tread long before rubber oxidation would become a problem, unless you are a car collector and wish to keep your prized possession for decades.

Personally, I have better things to waste my money on than $20 to fill up 4 tires with N2. What a scam!

As far as CO2, probably the same arguments apply. I haven't researched the diffusion rates and corrosivity of CO2, but I am skeptical. Again, the type of gas you use will have no bearing on the daily expansion and contraction of your tire. However, if you do choose to use CO2, you need to be aware that CO2 will combine with water to form carbonic acid, which is much more corrosive than the O2 within the air. Thus, you should try to use extremely dry CO2, and to displace most of the moisture (in the air originally in the tire) by filling/exhausting each tire several times.

Are you trying to say my salesman doest know about molecules? He sounded pretty convincing. I was imaging the nitrogen molecules being as big as beach balls floating around inside my little tires, never able to escape....I'm bummed, $45.00 donation for the unwanted frills. I would have rather been sold a fox tail or baby on board sign.

[mingoglia]

I appreciate the very thought out educated responses. I remember about a year ago I posted a very similar question on a car forum (not this forum) and got a bunch of, "I don't notice a difference" responses. It's nice to hear and talk about the science behind the question... and that's exactly what I was looking for.

Mike

[a priori]

Originally Posted by Shawn Clark

I doubt the higher partial pressure of CO2 would have any reaction effects with the alloys or rubber. This is the area of concern I would have. Some chemists would be more qualified to evaluate the materials (including the sensors) and the combination of water, CO2, and N2. CO2 itself should not condense/freeze at these temperatures and pressures.

If there is moisture (condensate) in the tire the CO2 will more readily dissolve in it than N2 or O2 if I'm not mistaken. If this is correct then there will be more pressure loss during colder operation.

I think the moisture question is the one that makes a difference here. It doesn't take much to get carbon dioxide to form carbonic acid in the presence of water. Of course you really need it to condense to cause much actual damage to the metals, and I think you are much more likely to see this in its preferred volatile state.

I'd prefer regular ol' air to straight nitrogen (for cost reasons), but I'd prefer either over carbon dioxide. You'd be safe if you purged the atmosphere in the tires, but why go to that effort? Put a muffler on your compressor motor or surround it with some noise-absorbing material!

[mingoglia]

Originally Posted by a priori

I think the moisture question is the one that makes a difference here. It doesn't take much to get carbon dioxide to form carbonic acid in the presence of water. Of course you really need it to condense to cause much actual damage to the metals, and I think you are much more likely to see this in its preferred volatile state.

I'd prefer regular ol' air to straight nitrogen (for cost reasons), but I'd prefer either over carbon dioxide. You'd be safe if you purged the atmosphere in the tires, but why go to that effort? Put a muffler on your compressor motor or surround it with some noise-absorbing material!

Do you think the aluminum wheel is more susceptible to this damage than steal would be? The reason why I ask is I've run a mixture of air from my compressor and CO2 in my Jeep for about 2 years now and the last time I had a tire off the rim I didn't see evidence of any corrosion. I deflate my tires to 10psi when on the trail and increase the pressure to around 26 for the drive home (when I don't trailer).... so about twice per month my tires are deflated, then re-inflated with co2. Now these wheels are steel and my Prius of course are aluminum.

Mike

[Huntceet]

PLUS! You've got some fire fighting ability there. Four tires filled with CO². You could go over to California and help put out fires.

Rod

[effwitt]

Ferrari runs CO2 in their Formula 1 cars because it works well for maintaining the desired temperature range during the race, but they also wear out a set of tires every 20 - 30 minutes of use...