Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

Does CO2 leak from tubes more rapidly than air?

Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Does CO2 leak from tubes more rapidly than air?

Old 09-15-17, 09:53 AM
  #1  
alfordjo
Member
Thread Starter
 
Join Date: Apr 2016
Location: Northern Colorado
Posts: 37
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 19 Post(s)
Likes: 0
Liked 7 Times in 3 Posts
Does CO2 leak from tubes more rapidly than air?

Last Saturday I went for a ride and got a flat near the end of my ride, about 2 miles from home. Once I get home after having a flat, I normally "empty" the tube that flatted and then pump up with air. (Removing most of the CO2.)

Since I was headed out of town for work on Monday, I failed to do this - I figured I would do it when I got back. Well, I got back Thursday afternoon to a very deflated tube/tire.

With the rash of flats I have had lately I just assume I did not properly install the tube from my last flat or more bad luck.

A thought then occurred to me, could it just be that CO2 "leaks" from tubes more quickly than air?
alfordjo is offline  
Old 09-15-17, 10:08 AM
  #2  
Sy Reene
Advocatus Diaboli
 
Sy Reene's Avatar
 
Join Date: Feb 2015
Location: Wherever I am
Posts: 6,334

Bikes: Merlin Cyrene, Nashbar steel CX

Mentioned: 11 Post(s)
Tagged: 1 Thread(s)
Quoted: 3236 Post(s)
Liked 550 Times in 397 Posts
Yes
Sy Reene is offline  
Old 09-15-17, 10:09 AM
  #3  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,289 Times in 808 Posts
Easy enough to set up a test, your self .. inflate 1 tire with each, to the same pressure, then time it.
fietsbob is offline  
Old 09-15-17, 10:34 AM
  #4  
VegasTriker
Senior Member
 
Join Date: Feb 2006
Location: Sin City, Nevada
Posts: 2,367

Bikes: Catrike 700, Greenspeed GTO trike, , Linear LWB recumbent, Haluzak Horizon SWB recumbent, Balance 450 MTB, Cannondale SM800 Beast of the East

Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 383 Post(s)
Likes: 0
Liked 73 Times in 58 Posts
Don't obsess with it. Technically speaking, a molecule of CO2 which has two atoms of oxygen and one atom of carbon is larger than the two most prevalent molecules in ordinary air which is approximately 78% nitrogen and 21% oxygen. All of these molecules are infinitesimally small. What really determines the rate at which your tube loses pressure is how many tiny holes are in the rubber itself. There's no reason to empty the CO2 out of your tube and replace it with air. Also don't waste your money on having tires filled with nitrogen at a service station. That's the biggest scam since the invention of bottled water.
VegasTriker is offline  
Old 09-15-17, 10:57 AM
  #5  
prathmann
Senior Member
 
Join Date: Nov 2008
Location: Bay Area, Calif.
Posts: 7,239
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 659 Post(s)
Likes: 0
Liked 3 Times in 2 Posts
Originally Posted by VegasTriker View Post
Don't obsess with it. Technically speaking, a molecule of CO2 which has two atoms of oxygen and one atom of carbon is larger than the two most prevalent molecules in ordinary air which is approximately 78% nitrogen and 21% oxygen. All of these molecules are infinitesimally small. What really determines the rate at which your tube loses pressure is how many tiny holes are in the rubber itself.
If it were really a question of molecules like tiny billiard balls bouncing off a rubber surface with some little holes then CO2 would actually stay inside the tube longer than either O2 or N2. But the chemistry comes into play. The CO2 has two carbon double bonds and these easily interact with the hydrocarbon compounds in rubber. As a result the CO2 molecules tend to stick to the rubber molecules and can gradually diffuse through the tube resulting in a gradual loss of pressure. The effect is easily noticed when you've used a CO2 cartridge to fill a tube instead of air.
prathmann is offline  
Old 09-15-17, 11:03 AM
  #6  
brianmcg123
Senior Member
 
brianmcg123's Avatar
 
Join Date: Oct 2002
Location: TN
Posts: 1,245
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 339 Post(s)
Liked 19 Times in 14 Posts
Yes
brianmcg123 is offline  
Old 09-15-17, 01:56 PM
  #7  
alfordjo
Member
Thread Starter
 
Join Date: Apr 2016
Location: Northern Colorado
Posts: 37
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 19 Post(s)
Likes: 0
Liked 7 Times in 3 Posts
Originally Posted by prathmann View Post
If it were really a question of molecules like tiny billiard balls bouncing off a rubber surface with some little holes then CO2 would actually stay inside the tube longer than either O2 or N2. But the chemistry comes into play. The CO2 has two carbon double bonds and these easily interact with the hydrocarbon compounds in rubber. As a result the CO2 molecules tend to stick to the rubber molecules and can gradually diffuse through the tube resulting in a gradual loss of pressure. The effect is easily noticed when you've used a CO2 cartridge to fill a tube instead of air.
I think I just got a Chemistry lesson!

Thanks for all the replies.

Jonathan
alfordjo is offline  
Old 09-16-17, 05:02 AM
  #8  
Hokiedad4
Senior Member
 
Join Date: May 2015
Location: South Jersey
Posts: 310

Bikes: Specialized Sirrus, Giant Contend

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 103 Post(s)
Liked 26 Times in 10 Posts
Originally Posted by prathmann View Post
If it were really a question of molecules like tiny billiard balls bouncing off a rubber surface with some little holes then CO2 would actually stay inside the tube longer than either O2 or N2. But the chemistry comes into play. The CO2 has two carbon double bonds and these easily interact with the hydrocarbon compounds in rubber. As a result the CO2 molecules tend to stick to the rubber molecules and can gradually diffuse through the tube resulting in a gradual loss of pressure. The effect is easily noticed when you've used a CO2 cartridge to fill a tube instead of air.
Carbon dioxide does not really interact with rubber. Butyl rubber is highly resistant to chemical interaction with most gases. But carbon dioxide diffuses through rubber much faster than air (relative permeability 2.9 versus 0.22 for air). So you're not going to ride around with CO2 in the tires, but it'll get you home.

The advantages of carbon dioxide are that it's easily compressed into a liquid and very safe. Nitrogen would work better but it can't be easily compressed into a liquid except at very low temperatures.

Last edited by Hokiedad4; 09-16-17 at 05:12 AM.
Hokiedad4 is offline  
Old 09-16-17, 06:16 AM
  #9  
Juan Foote
LBKA (formerly punkncat)
 
Juan Foote's Avatar
 
Join Date: Jan 2010
Location: Jawja
Posts: 3,739

Bikes: Spec Roubaix SL4, GT Traffic 1.0

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1247 Post(s)
Liked 214 Times in 154 Posts
No, actually being a heavier molecule it will leak slower, but the thing to point out is that CO2 is thermally induced to pressure (under pressure) where air isn't in a noticeable way. So, if it's really hot your tube will hold more pressure for volume than if it's cold.
Juan Foote is offline  
Old 09-16-17, 06:30 AM
  #10  
martianone
Senior Member
 
Join Date: Dec 2006
Location: Northern VT
Posts: 2,147

Bikes: recumbent & upright

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked 11 Times in 9 Posts
[QUOTE=Hokiedad4;19865162]Carbon dioxide does not really interact with rubber. Butyl rubber is highly resistant to chemical interaction with most gases. But carbon dioxide diffuses through rubber much faster than air (relative permeability 2.9 versus 0.22 for air).
........Source of this "data"?

Thanks!











So you're not going to ride around with CO2 in the tires, but it'll get you home.
martianone is offline  
Old 09-16-17, 07:46 AM
  #11  
prathmann
Senior Member
 
Join Date: Nov 2008
Location: Bay Area, Calif.
Posts: 7,239
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 659 Post(s)
Likes: 0
Liked 3 Times in 2 Posts
Originally Posted by Hokiedad4 View Post
Carbon dioxide does not really interact with rubber. Butyl rubber is highly resistant to chemical interaction with most gases. But carbon dioxide diffuses through rubber much faster than air (relative permeability 2.9 versus 0.22 for air).
It doesn't form new molecules by permanently bonding to the rubber, but the double bonds in CO2 can temporarily interact with the rubber hydrocarbon bonds. That's why the CO2 diffuses so readily through rubber - the temporary partial bonds makes for attraction between the CO2 and rubber molecules so they don't just bounce off each other.
prathmann is offline  
Old 09-16-17, 08:17 AM
  #12  
gregf83 
Senior Member
 
Join Date: Jun 2008
Location: Vancouver, BC
Posts: 9,009
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 1060 Post(s)
Liked 183 Times in 110 Posts
Originally Posted by Juan Foote View Post
No, actually being a heavier molecule it will leak slower, but the thing to point out is that CO2 is thermally induced to pressure (under pressure) where air isn't in a noticeable way. So, if it's really hot your tube will hold more pressure for volume than if it's cold.
Wrong and incomprehensible.
gregf83 is offline  
Old 09-16-17, 08:48 AM
  #13  
u235
Senior Member
 
u235's Avatar
 
Join Date: Mar 2017
Posts: 1,185
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 435 Post(s)
Liked 127 Times in 82 Posts
Let's take this beyond theory and apply it to real world.
Assuming one leaks faster then the other. Are we talking 0.5 psi increase in loss of CO2 vs regular air over a month? Considering I usually put a few psi of air in my tires every week anyway..
u235 is offline  
Old 09-16-17, 10:46 AM
  #14  
bobwysiwyg
Senior Member
 
bobwysiwyg's Avatar
 
Join Date: Jan 2016
Location: 961' 42.28 N, 83.78 W (A2)
Posts: 2,344

Bikes: Mongoose Selous, Trek DS

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 939 Post(s)
Liked 316 Times in 188 Posts
FWIW

Does CO2 leak out of tires? ? Exploring Overland
bobwysiwyg is offline  
Old 09-16-17, 04:50 PM
  #15  
DrIsotope
Non omnino gravis
 
DrIsotope's Avatar
 
Join Date: Feb 2015
Location: SoCal, USA!
Posts: 8,517

Bikes: Nekobasu, Pandicorn, Lakitu

Mentioned: 119 Post(s)
Tagged: 0 Thread(s)
Quoted: 4856 Post(s)
Liked 1,611 Times in 908 Posts
Definitely drops pressure faster, measured empirically, not though fancy maths. A tube pressured to ~100psi via a CO2 inflator will usually drop 10-20psi by the time I make it home, and be as low as 60-70psi by the time I get around to emptying it out the next morning.

But blissfully tubeless on all of our bikes now, so it's not really an issue anymore.
__________________
DrIsotope is offline  
Old 09-16-17, 05:01 PM
  #16  
wgscott
Occam's Rotor
 
wgscott's Avatar
 
Join Date: Jul 2013
Posts: 6,542
Mentioned: 61 Post(s)
Tagged: 0 Thread(s)
Quoted: 2366 Post(s)
Liked 1,614 Times in 812 Posts
Originally Posted by VegasTriker View Post
Don't obsess with it. Technically speaking, a molecule of CO2 which has two atoms of oxygen and one atom of carbon is larger than the two most prevalent molecules in ordinary air which is approximately 78% nitrogen and 21% oxygen. All of these molecules are infinitesimally small. What really determines the rate at which your tube loses pressure is how many tiny holes are in the rubber itself. There's no reason to empty the CO2 out of your tube and replace it with air. Also don't waste your money on having tires filled with nitrogen at a service station. That's the biggest scam since the invention of bottled water.
CO[sub]2[/sub] is larger than nitrogen and oxygen, but it passes through the inner tube rubber much more readily due to increased permeativity.
wgscott is offline  
Old 09-16-17, 07:50 PM
  #17  
a1penguin
Senior Member
 
a1penguin's Avatar
 
Join Date: Jun 2009
Location: Silicon Valley, CA
Posts: 3,189
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 134 Post(s)
Liked 15 Times in 10 Posts
Technical Q&A with Lennard Zinn - Large molecules and short frames | VeloNews.com


"Alan Hills:

I’ve been told it was true by no less than (our local triathlon legend) Dave Scott. Wading through the web yields some insights on tire pressure loss from tires/tubes inflated with carbon dioxide (CO2) cartridges. Two polymers are used for bike tubes; latex rubber and butyl rubber (isobutylene rubber).

Butyl rubber dominates the market and is used for almost all tubeless tires and bike tubes as its permeability to air is incredibly low — butyl tubes have only 10 percent the leakage rates of natural latex rubber tubes.

Permeation by diffusion predicts gas leakage rates proportional to the inverse of the square root of their molecular weights. Using air as a reference the predicted leakage rates for common gases are: helium 2.7, air 1.0, nitrogen 1.02, oxygen 0.95, argon 0.85, carbon dioxide 0.81.

It turns out however that the leakage rate of CO2 is huge, and the reason is that it is actually soluble in butyl rubber and is thus not constrained to normal permeation loss, it can transfer straight through the bulk rubber resulting in severe tire pressure loss on the order of a single day. CO2 is not likely to be replaced by argon or other gases in refill cartridges, however, because CO2 is much more easily liquefied than other gases and can be contained in a moderate-pressure cartridge in a patch kit. An analogous cartridge holding N2 or argon (non-liquified gas) would be dangerous and would require a thick (and very heavy) steel-walled storage vessel. A reference dealing with CO2 transfer through latex rubber sheds light on the loss process."
a1penguin is offline  
Old 09-17-17, 11:49 AM
  #18  
Sy Reene
Advocatus Diaboli
 
Sy Reene's Avatar
 
Join Date: Feb 2015
Location: Wherever I am
Posts: 6,334

Bikes: Merlin Cyrene, Nashbar steel CX

Mentioned: 11 Post(s)
Tagged: 1 Thread(s)
Quoted: 3236 Post(s)
Liked 550 Times in 397 Posts
Originally Posted by alfordjo View Post
I think I just got a Chemistry lesson!

Thanks for all the replies.

Jonathan
Welcome to BF! Where there is no such thing as a Yes/No question
Sy Reene is offline  
Old 09-18-17, 06:16 AM
  #19  
Juan Foote
LBKA (formerly punkncat)
 
Juan Foote's Avatar
 
Join Date: Jan 2010
Location: Jawja
Posts: 3,739

Bikes: Spec Roubaix SL4, GT Traffic 1.0

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1247 Post(s)
Liked 214 Times in 154 Posts
Originally Posted by gregf83 View Post
Wrong and incomprehensible.

Hi


Do you know why co/co2 detectors are placed within a foot of the ground?

Are you familiar with this chart?

https://thehotpepper.com/uploads/mont...1463862733.gif

Last edited by Juan Foote; 09-18-17 at 07:43 AM.
Juan Foote is offline  
Old 09-18-17, 08:06 AM
  #20  
gregf83 
Senior Member
 
Join Date: Jun 2008
Location: Vancouver, BC
Posts: 9,009
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 1060 Post(s)
Liked 183 Times in 110 Posts
Originally Posted by Juan Foote View Post
Hi


Do you know why co/co2 detectors are placed within a foot of the ground?

Are you familiar with this chart?

That's a useful chart if you're interested in the temperature and pressure at which CO2 liquifies, however, I prefer a gas in my tires rather than a liquid. And my tires aren't rated for 400psi.

It still leaks out of butyl tubes faster than air. Keep searching for charts.
gregf83 is offline  
Old 09-18-17, 08:13 AM
  #21  
Juan Foote
LBKA (formerly punkncat)
 
Juan Foote's Avatar
 
Join Date: Jan 2010
Location: Jawja
Posts: 3,739

Bikes: Spec Roubaix SL4, GT Traffic 1.0

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1247 Post(s)
Liked 214 Times in 154 Posts
Originally Posted by gregf83 View Post
That's a useful chart if you're interested in the temperature and pressure at which CO2 liquifies, however, I prefer a gas in my tires rather than a liquid. And my tires aren't rated for 400psi.

It still leaks out of butyl tubes faster than air. Keep searching for charts.
The chart is meant for for co2 tanks/paintball applications. It carries over to any powerlet of co2 What it demonstrates though, is the volatility of it's pressure, even in aerosol state, at temperature. As we can see from this chart that difference is notably less at lower pressures but still there. I know I can feel five pounds difference in my little bitty tires.

Edit- To add to that. A co2 powerlet has no gauge. We have no idea what our tire is actually at, it's just not "flat". Considering the volume of tire and size of the powerlet (which can be adjusted) it is safe to assume that most powerlets aren't actually putting the recommended amount of 80-110 (w/e) PSI in the tire in the first place. It's just good to ride home.
You get home, the tire cools, it looses a bit more of the unsure whether it was the right pressure that it had, and the perception is that your tire went flat faster.

Last edited by Juan Foote; 09-18-17 at 08:23 AM.
Juan Foote is offline  
Old 09-18-17, 08:36 AM
  #22  
gregf83 
Senior Member
 
Join Date: Jun 2008
Location: Vancouver, BC
Posts: 9,009
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 1060 Post(s)
Liked 183 Times in 110 Posts
Originally Posted by Juan Foote View Post
The chart is meant for for co2 tanks/paintball applications. It carries over to any powerlet of co2 What it demonstrates though, is the volatility of it's pressure, even in aerosol state, at temperature. As we can see from this chart that difference is notably less at lower pressures but still there. I know I can feel five pounds difference in my little bitty tires.

Edit- To add to that. A co2 powerlet has no gauge. We have no idea what our tire is actually at, it's just not "flat". Considering the volume of tire and size of the powerlet (which can be adjusted) it is safe to assume that most powerlets aren't actually putting the recommended amount of 80-110 (w/e) PSI in the tire in the first place. It's just good to ride home.
You get home, the tire cools, it looses a bit more of the unsure whether it was the right pressure that it had, and the perception is that your tire went flat faster.
Hokiedad4 had the correct explanation earlier in post #8.
gregf83 is offline  
Old 09-18-17, 08:39 AM
  #23  
Juan Foote
LBKA (formerly punkncat)
 
Juan Foote's Avatar
 
Join Date: Jan 2010
Location: Jawja
Posts: 3,739

Bikes: Spec Roubaix SL4, GT Traffic 1.0

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1247 Post(s)
Liked 214 Times in 154 Posts
Originally Posted by gregf83 View Post
Hokiedad4 had the correct explanation earlier in post #8.
That post was refuted in 17.



Anyway, not going to sit and argue all day over it. Neat emergency stuff to have on hand. Shouldn't be left in long enough for the rest to matter.
Juan Foote is offline  
Old 09-18-17, 08:47 AM
  #24  
DrIsotope
Non omnino gravis
 
DrIsotope's Avatar
 
Join Date: Feb 2015
Location: SoCal, USA!
Posts: 8,517

Bikes: Nekobasu, Pandicorn, Lakitu

Mentioned: 119 Post(s)
Tagged: 0 Thread(s)
Quoted: 4856 Post(s)
Liked 1,611 Times in 908 Posts
Originally Posted by Juan Foote View Post
You get home, the tire cools, it looses a bit more of the unsure whether it was the right pressure that it had, and the perception is that your tire went flat faster.
Have you ever actually used a CO2 cartridge? There's this thing it does when it leaves the cartridge rapidly, which is it gets really, really, really cold. Unless the outside temperature is at or below freezing, a fixed flat filled with CO2 should be warmer and therefore at a higher PSI when getting home... if it weren't for the incontrovertible fact that CO2 diffuses right through the butyl rubber.
__________________
DrIsotope is offline  
Old 09-18-17, 09:11 AM
  #25  
Juan Foote
LBKA (formerly punkncat)
 
Juan Foote's Avatar
 
Join Date: Jan 2010
Location: Jawja
Posts: 3,739

Bikes: Spec Roubaix SL4, GT Traffic 1.0

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1247 Post(s)
Liked 214 Times in 154 Posts
Originally Posted by DrIsotope View Post
Have you ever actually used a CO2 cartridge? There's this thing it does when it leaves the cartridge rapidly, which is it gets really, really, really cold. Unless the outside temperature is at or below freezing, a fixed flat filled with CO2 should be warmer and therefore at a higher PSI when getting home... if it weren't for the incontrovertible fact that CO2 diffuses right through the butyl rubber.
Yes, I understand this. I also understand that that cartridge is about 700 or so PSI according to the temp outside, and even WITH the cooling doesn't drop below a few hundred. In spite of this, it isn't pumping the tire to 80psi in most cases, or even less. During the process of cooling the cartridge it's flashed to gas, and warmed a significant amount.

The other aspect is that you shouldn't be leaving CO2 (which is acidic) in a tube to be eating the rubber anyway.

Once again. Emergency get you home device.
Juan Foote is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.