Originally Posted by
FBinNY
While it's true that CO2 permeates through butyl faster than air, it's not really relevant in the real world of bicycling. The difference isn't that large, so there will be a faster pressure loss over time in hours or days, but not over minutes of an hour or two.
So if you fill your tire on the road, you can rest assured that there's plenty of time to get home. Next time you top off you'll be replacing the CO2 with air, so the rate of air loss on the new mix will be slower, and with each top off cycle the percentage of CO2 left will be reduced until there's virtually none left.
All in all, the talk about CO2 is totally academic except for those who like to debate immaterial issues.
Well the reason the question came up when I was digging into it was a friend that had some kind of CO2 inflation system that he used on dirt bikes, and dirt bike trailers, etc, and his mountian bike tires were BOTH losing stupendous amounts of pressure in just 3-4 days....and eventually it all boiled down to using CO2 instead of air.
His CO2 use was not typical of most bicyclists....but interesting nonetheless :-).