Al1943

Goes to show you can learn just about anything from a cyberspace bike forum, some of it is even true.

Al

Mentor58

It ain't over till we SAY it's over....

SMW

supcom

CO2 filled tires do not go flat faster than air filled tires! They just more efficiently achieve equilibrium with the atmosphere.

2manybikes

This is the all around best explanation....

https://www.doc.ic.ac.uk/~ids/dotdot/...ncabulator.txt

RockyMtnMerlin

On another note, no reply yet to the email I sent to the inflation boys.

2manybikes

Just make sure they don't disconnect the pantametric petometer from the spiral wayneshaft.

A friend of mine actually submitted that paper as a high school science project. The teacher liked it so much he had it copied for everyone.

jscott

Now that we all read the internet for CO2 who also read about the resonant forms and CO2 vibrating this is the wiggling form that is polar for a short time and causes the increased permieability. Thats the interesting chemistry

scooby

I just found this thread after testing my CO2 inflator for the first time. I wondered what the heck happened!

I filled one tire with CO2 and the other with air from my compressor. Both (new) tires were filled to 110 psi. After a week the air tire was down to 100 psi and the CO2 tire was down to 60 psi.

I found this scholarly answer that might help explain things:
https://www.madsci.org/posts/archives...2329.Ch.r.html

byte_speed

I have experienced this a number of times. The first time the tire went flat overnight. I took the (brand new, no patch) tube back out of the tire to patch the "hole". I inflated the bare tube to about 4" in diameter and immersed it in a bucket of water, no bubbles. Put the tube back, filled it with air to 100 psi and it lost only a pound or two in the next week.

I'm a chemcial engineer and went through the same thought process as you. Somebody on this site gave me a link to a site with the solubility of various gassses in various materials https://www.diffusion-polymers.com/gas_diffusion.htm. Notice that CO2 solubility in butyl rubber is 12x more than nitrogen. I'm not sure this is the whole story, but I can assure you this is no urban myth.

al-wagner

So instead of making CO2 cartridges why not air or nitrogen???

filtersweep

CO2 is safer.

2manybikes

in the early 1990's Innovations said it leaks out on the instructions. They warned you to fill up your tire the next day.

thebchessl

Here is a test of useless knowledge. How many PSI the is the co2 in a cartridge?

HillRider

CO2 is liquid at the pressure in the cylinders so the content is a lot greater than the amount that would fit if it were a gas at the same pressure. To get O2 or N2 in adequate amounts (they won't liquify at any pressure at room temperature) the cylinder pressure would have to be enormously (and dangerously) high.

cyccommute 

856 psi at 70 F

2manybikes

He said it was useless!

DiabloScott

I've heard the permeability description before, and I'm a smart guy but not a chemist. Is there a difference between the CO2 "permeating" its way out, and just wiggling its way through the rubber molecules? Do the properties of the rubber change during this permeating process?

freeranger

CO2 inflated tubes do go flatter quicker. I think Al Gore said it had something to do with global warming.

cyccommute 

Tomanybikes has a link to a good explanation. The rubber probably swells ...not as much as if it were in contact with a liquid solvent...because it a solvent process not just a permeability issue. This would open any pores in the elastomer and make it more permeable. However, I doubt if any change would be permanent. Remove the CO2 and it would shrink back to normal.

AndrewP

"osmosis" is the process whereby molecules pass through a membrane to equalize the concentration on both sides. Since there is a very low concentration of CO2 in the air outside the tire the CO2 will pass through the tube until it has brought the CO2 level outside the tire to match the concentration inside. Temperature and pressure differences will affect the speed at which the molecules go through the membrane.

DiabloScott

Interesting, I hadn't thought of this in terms of osmotic pressure; ie, if the CO2 pressurized tire were stored in a CO2 rich environment, would it still go flat?

SoonerBent

I had my first flat in forever last Saturday. Used the CO2 to inflate the rear tire. Bike has sat in it's room since finishing the ride so now I want to get home and see if the rear is flat or lower than the front.

benten biker

The CO2 problem in tires is not new and no different than leaving a carbonated beverage packaged in a plastic bottle around for a while, it goes flat. I just ran across an article from 1967 (https://www.pubmedcentral.nih.gov/pic...5&blobtype=pdf) where a study was completed regarding the permeability of CO2 through various membranes. Rubber seems to have the highest permeability of all of the materials tested and it was the thickest. The bottom line as someone pointed out, is that CO2 is meant to just to get you home. If the pressure holds more than a day, you’re doing good.

About a year ago, I ran across a couple of guys that were developing an inert gas mixture that had would not permeate through tires. They filled up my mountain bike tires 10 months ago to 55 psig and my tires are still at 55 psig and I have not had to break out the tire pump yet. It’s kind of nice to be able to pull the bike off the rack and hit the road without the ritual inflation; I’m spoiled for life now.

Before writing this post, I called these guys and they are planning on rolling out their gas product under the name Stayfill which will be packaged in the same size cartridge as the CO2 so it will be a drop in replacement for those of us with the CO2 fill valves. They expect to have their website up and running in 3-4 weeks and selling product. I believe their website is like the name: www.stayfill.com.

Retro Grouch 

Yup. Some people waste too much time going to school and reading books that would be better spent riding their bikes and observing what's really happening in the world.

I don't worry about defilating my tires, however, I simply top up my tires before every ride and the CO2 leakage eventually takes care of itself.