I agree. I have never noticed a CO2 filled tire needing to be re-filled more quickly. Perhaps it was not completely filled?Quote:
Originally Posted by Veronica
I must again post from Sheldon Brown's alter ego:
Quote:
Originally Posted by Carapace Completed Umber
the same thing has happened to my husband and myself. i asked my lbs about it the first time and they said that it must have been a fluke. then it happened to my husband as well. i believe it based on my experience. and both times they were completely full. once i refilled with my floor pump they held air just fine. but have never had co2 hold.
Before I knew better, I didn't always pump my "road" tires before every ride. On my mtn bike (now my commuter bike), I never pumped everytime I rode. I felt the tire and if the tire felt 'squishy' I would pump it up. But, on a group ride, on my road bike, I had a flat. The group leader that helped me fix the flat told me that as soon as I got home, I should pump up my tire. He said that the CO2 air didn't hold the air the same as my pumped air. Sure enough, I got home OK, but the next morning, my road tire felt really squishy, so I pump it up, fearing I would have another flat the next time I checked. My pumped tire remained good and by the next weekend, when I pumped up the tires for another long ride, my tires needed pumping, but not as much as it did the day after my CO2 fill. On my mtn bike (now commuter bike), I have had lots of flats this summer. My CO2 would fill it for me till I could get the tire fixed, but I would never feel like I was 'safe' until I actually put pumped air in the tire. I think the CO2's are good for the emergency fix, but not good for the long haul and if I have access to a regular pump, I will pump my tires for good measure.
CO2 works great! I used cylinders whenever needed and simply top off with a regular pump before every ride. I've not found any problems with tires loosing more air when filled with CO2, however some tubes leak more then others. I've had some I rarely had to add air, and other that would lose 10 psi in a day.
I usually dont have flat or squishy tires after using a CO2 cartridge, but I pump up the tires with a floor pump before every ride anyway.
If the tire does go flat after use on a ride, is it possible that something embedded in the tire is causing it, instead of the CO2? After all, the only reason to use one during a ride is if something is wrong with your tire and tube. Even if the tube is replaced, the problem still persists if something too small to be seen remains in your tire.
I had that happen once. After a succession of flats on one ride, close inspection at home revealed a tiny, tiny shard of a staple embedded in the tire.
I always pump my tires before every ride, but, neither my husband or I have had issues with CO2 cartridges. I've only had flats 3 times in 8 years; one, where the tire kept going flat was because the tire had actually been cut.
I think this is what my grandmother called a "bubbie-meiser."
Ah, more info here:
http://www.ornl.gov/~webworks/cppr/y...res/117378.pdf
According to that (discussion of separation of gases by a permeable membrane - effectively similar to permeation of molecules through an inner tube), CO2 molecules actually have a larger effective hard sphere diameter than N2 molecules - 3.99 Angstroms for CO2 vs. 3.68 for N2.
So there goes that theory :rolleyes:
whew!!! Glad some one looked it up about the effective size of the two molecules. Carbon, nitrogen and oxygen are on the second row of the periodic table, with carbon in group IV followed by Nitrogen and finally by Oxygen. So when someone said CO2 is smaller than N2 :confused: huh?
Now about the permeability, just because something has an effectively larger diameter doesn't make it less permeable. Things that can affect is the Van-der-Waal force (something that poped up first in my head) and I'm sure there are others. but this can create drag on a molecule as it tries to permeate across a membrane.
I dunno whether CO2 will go flat faster than N2 filled tire. CO2 has a molar weight of 12+16+16=44 while nitrogen is 28. assuming both act as an ideal gas up to 100psi (PV=nRT law)... how much more does CO2 filled tire weigh than with N2?? if someone can figure out what n, number of moles to fill up a tire, then we would know the difference in weight. my P-Chem book is burried somwhere in the garage. And I'm in no mood to go look up the conversion factors and the value of ideal gas constant R...
Anyway, not sure which would leak faster. And that's my answer. Answer from your LBS sounds fishy.
smilingcat
I can't believe what a controversial thread I started! I told my husband not to feel too bad that he didn't know about the C02, because it's obviously not known by many and, in fact, is debated as truth by many. He says it makes perfect sense, though. And he said this explains why he sees tires being filled with pumps at the Tour de France. He could never figure out why they wouldn't just use an air compressor, which would be so much quicker.
We, too, fill our tires before every ride. And this would explain why dh never realized the C02 had leaked so much. He just pumped it no matter what. I agree that different tubes, tires and the weather may account for the C02 leaking faster or slower. I think the "18 hour" thing the LBS guy said was just a number he threw out to say you can ride quite a while, but it won't last forever. He wasn't being specific.
our room mate works for a welding supply shop, so he knows a bit about gasses. co2- bigger.
Now helium- smaller, which is why it escapes balloons so quickly..
ya learn something new every day
Um, an "air compressor" (like you have in your garage) compresses and delivers AIR. They could use pre-filled nitrogen cylinders... but why?Quote:
Originally Posted by Jiffer
In high-level pro races they just swap wheels... so how long it takes to fix the flat is pretty much irrelevant.
I think the reason they use pumps in that context is control. You know how you fill a great big auto or motorcycle tire from a compressor - go over by a couple-three pounds and then let the air out with the valve in your gauge, right? Leaving the compressor on a skinny road bicycle tire for that extra second or even half-second could be enough to blow it clear off the rim. (BTDT at gas station compressors when I was a kid :rolleyes:) By the time you check and adjust the pressure several times, it's just as quick to pump a road bike tire by hand - with a decent floor pump it only takes 25-30 strokes to go from 0 to 120 (it seems like... I'll count them next time!)
Interesting news, y'all are serious investigators on this stuff! I've never used a CO2 cartridge. They did not exist for cyclists when I started riding in the 80s, so I've always carried a pump with me. My Road Morph gets me up to 100 PSI without any problems. CO2 cartridges can fail and people use them incorrectly, and if you don't have a pump, you're plum outta luck. Also, what do you do with the spent cartridges--just throw them away? That seems like such a waste somehow.
So even if you use CO2 cartridges, you might still want to have a pump for backup.
N2 is a smaller molecule (2 atoms of N) than CO2 (1 atom of C and 2 of O). However, because our atmosphere is 78% N2, the N2 would escape more slowly because of the principle of diffusion. Thus, CO2 would escape quickly because there is less than 1% CO2 in the atmosphere and to reach equlibrium, the CO2 would have to move OUT of the tire. In the case of N2, equilbrium is reached quicker because there is more N2 in the outside of the tire (atmosphere). Sorry for the chemistry lesson, I have a BS in it.
Mistie - How 'bout the other interactions between the rubber of tires (the stuff smilingcat brought up) and CO2 vs. N2? Surely equilibrium isn't the only thing that determines how quickly you lose pressure in a tire?
Air is a combination of about 80% nitrogen and 20% oxygen. Carbon dioxide is actually more dense than air.Quote:
Originally Posted by kermit
If you mix vinegar and baking soda together in a container with a lighted candle, the candle will go out since the carbon dioxide produced pushes the air (lighter) up and the carbon dioxide (heavier) stays in the bottom and extinguishes the flame.