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Old 10-15-11, 06:25 PM   #1
Mithrandir
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Probably a stupid question: CO2 in tire

So I've read in multiple places that when you fill a tire with CO2, you should fully deflate it when you get home, and reinflate it with air. I recall the reasoning was that CO2 escapes quicker from tubes than normal air. *

So, I've got large tires. 26x2.0. Lot of volume. I use 2 cartridges to fill them up, and when I get home, I deflate them. But every time I deflate them, I wonder to myself "is there enough volume of CO2 in there that it could cause me to not breathe in enough oxygen and hurt myself?". So I usually just deflate them in small bursts. I'm not a physics or biology major, but something tells me I'm probably worried over nothing; there's probably not enough volume in the tire, even if it's deflating near my face, to cause a notable lack of oxygen for a long enough period to make any of a difference whatsoever. But I'd just like to know if anyone knows this for sure?


* - I'm not even sure how much sense this makes, since it seems to me that CO2 molecules are larger than nitrogen molecules, which make up the majority of air... so is it even true that CO2 escapes quicker than normal air?
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Old 10-15-11, 06:30 PM   #2
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1. Butyl rubber doesn't retain CO2 well. Sounds strange, but it's true.

2. You don't need to worry about suffocation from 30 grams of CO2, it's cool.

3. You could also consider using the Big Air cartridges, which are a 40-gram propane cartridge, if you happen to be in a time-critical situation. That's what I use for XC racing.
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Old 10-15-11, 06:46 PM   #3
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Agreed. CO2 does diffuse through the tube much faster than either the O2 or N2 molecules in regular air. The reason is chemical rather than mechanical. The carbon double bonds in CO2 can temporarily interact with the carbon bonds in the rubber and momentarily bind the CO2 to the rubber. It can then migrate through the tube and some of the molecules eventually make their way to the outside.

The total volume of CO2 inside your one of your tires inflated to 75 psi is less than one cubic foot. It'll quickly disperse throughout the room (800 cu. ft. in a 10' x 10' x 8' space) and comprise a negligible percentage of the air - there'll still be plenty of O2.

You don't really need to deflate the tire. If you leave the CO2 in there it'll leak out very slowly so you'd need to top off the tire periodically to keep the pressure constant - but that's not a major problem. Eventually most of the CO2 will be gone anyway.
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Old 10-15-11, 06:51 PM   #4
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CO, carbon monoxide, is the stuff that is dangerous. It can build up to dangerous amounts without us being aware of it. CO2, on the other hand, causes suffication--you'd know if there was too much CO2.
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Old 10-15-11, 07:05 PM   #5
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CO, carbon monoxide, is the stuff that is dangerous. It can build up to dangerous amounts without us being aware of it. CO2, on the other hand, causes suffication--you'd know if there was too much CO2.
You mean your ghost would know, don't you?
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Old 10-15-11, 07:14 PM   #6
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In my 700x23 tires, a CO2 inflation will be soft the next day and totally flat in two days. The reason to empty it out and fill it up with air when you get home is so you don't think you have a puncture when you're starting your next ride. Might as well purge and repress.
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Old 10-15-11, 07:15 PM   #7
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You mean your ghost would know, don't you?
No, your ghost would know if there was too much CO...oops.

The CO2 would be apparent while you were still kicking.
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Old 10-15-11, 07:20 PM   #8
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As others say, CO2 does leak out a little faster than air. But I think this gets overplayed. I've read past posts on this and another forum that make it sound like you better run home as soon as you inflate your tires, or else you will flat again. Truth is the leak is not that bad and I never drain my tires. Just keep a check on the pressure and inflate as you usually do. As Prathman above explained, you're in no danger of suffocating.
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Old 10-15-11, 08:30 PM   #9
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So I've read in multiple places that when you fill a tire with CO2, you should fully deflate it when you get home, and reinflate it with air. I recall the reasoning was that CO2 escapes quicker from tubes than normal air. *

So, I've got large tires. 26x2.0. Lot of volume. I use 2 cartridges to fill them up, and when I get home, I deflate them.
WAIT! are you saying you routinely inflate your tires with CO2 cartridges? I never deflate a spare I usea CO2 on while riding. Although I should be deflating it since I need to glue the new tire on
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Old 10-15-11, 08:48 PM   #10
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CO2 is harmless; it's what you exhale and plants inhale. Not enough CO2 in a tire to suffocate anyone.

CO on the other hand, will cause you to see ghosts, then kill you.
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Old 10-15-11, 08:53 PM   #11
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1. Butyl rubber doesn't retain CO2 well. Sounds strange, but it's true.

2. You don't need to worry about suffocation from 30 grams of CO2, it's cool.

3. You could also consider using the Big Air cartridges, which are a 40-gram propane cartridge, if you happen to be in a time-critical situation. That's what I use for XC racing.
I've always wondered how smart it was to use propane in a bycycle tire.
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Old 10-15-11, 09:08 PM   #12
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WAIT! are you saying you routinely inflate your tires with CO2 cartridges? I never deflate a spare I usea CO2 on while riding. Although I should be deflating it since I need to glue the new tire on
LOL no. I just get a lot of flats. I only use the CO2 when I'm in a rush. Unfortunately it does happen too often.
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Old 10-15-11, 09:10 PM   #13
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I've always wondered how smart it was to use propane in a bycycle tire.
It's better to use nitrous oxide, then at least you can take a big hit off the gas first then be laughing about putting air into the tires...that could make riding fun again!
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Old 10-15-11, 10:01 PM   #14
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It's better to use nitrous oxide, then at least you can take a big hit off the gas first then be laughing about putting air into the tires...that could make riding fun again!
Or helium, so you can talk funny
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Old 10-16-11, 02:29 AM   #15
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Or helium, so you can talk funny

Or sulfur hexa-flouride and talk funnier.
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Old 10-16-11, 04:31 AM   #16
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Helium, yeah. I figure the weight weenies would be filling their tires with Hydrogen or Helium.
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Old 10-16-11, 08:41 AM   #17
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Helium, yeah. I figure the weight weenies would be filling their tires with Hydrogen or Helium.
I believe some track riders did fill their tires with Helium. It was supposed to somehow reduce rolling resistance as well as weight. It difuses out of the tube much more quickly than air but track events are very short and the refill cylinder was always close by.

As to suffocating from the CO2 let out of a tire, keep in mind that a typical person, while moderately active, will exhale something like 150 grams of CO2 per hour so don't stay in a closed garage while breathing if you are concerned about that.
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Old 10-16-11, 12:13 PM   #18
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CO2 is the stuff that puts bubbles in your coke.

Apparently there can be 4-7 grammes of CO2 per ml of coke - I don't know how much is consumed and how much is lost to the atmosphere, but that would put between 1.32 and 2.31 KG of CO2 in a 330ml can (not sure how that works).

Maybe they meant per litre.

Don't forget also there are CO2 fire extinguishers, which contain far more CO2 and are release direcly (these only work in confined spaces too.

Last edited by CaptCarrot; 10-16-11 at 12:18 PM.
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Old 10-16-11, 12:34 PM   #19
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I'd be surprised if there was more than 5 grams in a can of coke. Last I recall, flat coke weighs about the same as a fresh coke.
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Old 10-16-11, 03:08 PM   #20
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CO2 triggers the breathing reflex. If you try to take a huff of CO2, you will immediately gasp for air. Your body is very good at sensing CO2. If you try to take a huff of nitrogen, you won't even notice it. Helium, the same. The same is true for a lot of gasses. CO2 will make you want to breathe. It is like that sensation of holding your breath while diving underwater, and staying down for as long as you can. As you try to race to the surface, that strong urge to get some fresh air is caused by the CO2 forming in your lungs.
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Old 10-16-11, 03:32 PM   #21
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I'd be surprised if there was more than 5 grams in a can of coke. Last I recall, flat coke weighs about the same as a fresh coke.
Yes, but gases are notoriously difficult to weigh due to the fact that they are a gas. When suspended in liquid I think I am right in saying it is still a gas. CO2 requires extreme pressure or extreme cold to liquefy.

Density
1.562 g/mL (solid at 1 atm and −78.5 C)
0.770 g/mL (liquid at 56 atm and 20 C)
1.977 g/L (gas at 1 atm and 0 C)

Melting point
-78 C, 194.7 K, -109 F (subl.)

Boiling point
-57 C, 216.6 K, -70 F (at 5.185 bar)

Solubility in water
1.45 g/L at 25 C, 100 kPa

Solubility in water however, doesn't count the forced injection process of carbonizing water - so the figures I posted before may hold some weight (no pun intended) - that said, I'm not entirely sure I believe them either.
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Old 10-16-11, 04:13 PM   #22
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CO2 is harmless; it's what you exhale and plants inhale. Not enough CO2 in a tire to suffocate anyone.

CO on the other hand, will cause you to see ghosts, then kill you.
It's not harmless, it's toxic. A 1% concentration of CO2 causes drowsiness. Above 5% cause dizziness and above 8% unconsciousness after 5-10 minutes. The OSHA short term exposure limit is 3%. It has nothing to do with suffocation, and happens regardless of oxygen level. The gas itself is toxic. Ever seen Apollo 13? The problem wasn't lack of oxygen, but too much CO2.

Now, if you manage such concentrations via deflating a tube, you're doing something wrong. But CO2 is far from harmless. (Though not as dangerous as CO, of course).
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