Bike share in New York reportedly fills their tires with nitrogen. They say so here (scroll down to where they mention tires):
I'm not sure I see the point.
Interesting, but if you read into it carefully, I don't think the marginal benefits are really there for cyclists.
They're measuring benefits for fleets of trucks doing 2500 miles a week; static test losses of a few psi over hundreds of hours. I'm not suggesting that this translates directly, but certainly doesn't look "tasty" for us...
Ride no faster than your Guardian Angel can fly!
I think I'll just buy the green valve cover so all my friends THINK I have nitrogen in my bike tires.
Concerning the CO2 global warming aspect, we are talking about ridiciously small volumes here. Considering that the air you exhale contains up to 4% carbon dioxide, you probably will add more to the greenhouse effect by simply breathing as you take care about your tyre business. And the CO2 found in the cartridges probably (well ok, likely in my eyes FWIW) isn't the lucrative incentive for the industry behind it - this snip is from the Universal Industrial Gases website:
"The concentration of CO2 in air and in stack gases from simple combustion sources (heaters, boilers, furnaces) is not high enough to make carbon dioxide recovery commercially feasible. Producing carbon dioxide as a commercial product requires that it be recovered and purified from a relatively high-volume, CO2-rich gas stream, generally a stream which is created as an unavoidable byproduct of a large-scale chemical production process or some form of biological process. In almost all cases, carbon dioxide which is captured and purified for commercial applications would be vented to the atmosphere at the production point if it was not recoved for transport and beneficial use at other locations."
Last edited by CbadRider; 05-08-14 at 01:57 PM. Reason: Copyright violation - quoted sources must contain a link to the source. Added link.
I did some calculations using the figures on the Prestacycle site (which sells a Nitrogen inflation system) for the rates at which oxygen and nitrogen escape. Starting from a mixture of ordinary air, you'll have nearly pure nitrogen (plus residual moisture) when the tire slips to about 70% of its initial psi. If you wait until then to refill, the newly refilled tire will be about 93% nitrogen and will hit pure nitrogen at about 90% of psi. Refill again at that point and you'll be at 98% nitrogen. From there, vigilant re-inflation will keep you very near pure oxygen using just a simple floor pump. The key is to let it drop to 70% before the first re-inflation.
Of course, most people probably let their tires drop to around 80-90% of ideal psi before topping it off, so they're condemned to always hover at around 90% nitrogen.
Yes, I'm a geek.
To offer something a bit more practical, finding tubes that minimize air leakage is probably a much better investment than inflating with nitrogen.
I'm very particular about the gas with which I fill my tires. I've settled on a 78% nitrogen blend. I use it in the cars too.
CO2 exhaled by an average person: 900 grams per day, or average 37 grams per hour. So a 16 gram CO2 cartridge is the equivalent of 25 minutes of breathing out, and even fewer minutes when working hard.
Woah, I didn't expect 900 grams per person per day. But I also didn't know that air is 7.5 pounds per cubic foot. That's way heavier than I expected. No wonder it's hard to go fast on a bike, the rider has to shove all that weight of air out of the way.
Last edited by rm -rf; 05-07-14 at 08:30 PM.
Thanks for that post. I was belly laughing at the his original CO2 post. Maybe if he stops breathing he will greatly reduce his carbon footprint.
N2 is dirt cheap, so the fact that some people charge extra for it is goofy. I suspect they release a considerable amount of it back into the atmosphere when they pull it out of air. At work, I actually pay more to rent the tank for a month than I do for the gas, it's something like $4. I imagine that anyone that has to carry a bottle of gas around to fill up bike tires with would do pretty well using N2, you can go get a bottle and it will last for quite a few tires. Nobody bottles dry air.
i like Conti tubes.
Regarding the environmental aspect, I realized that I didn't know where it actually came from, to put into those little cylinders. From what I can find, it has to start as a high volume CO2-rich gas, which is generally a byproduct from a large-scale chemical process. In other words, released into the atmosphere if it wasn't bottled up for bike tires. So I don't think we need to feel guilty about contributing to the greenhouse effect.
I take it with a grain of salt since my sources were all from the commercial end, such as Bulk Liquid Carbon Dioxide > Air Liquide UK but it sounds plausible to me.
As bjorsa points out above, the CO2 in a cartridge isn't recovered from the atmosphere. It is obtained from processes that produce large CO2 streams. That means the fossilized carbon that was removed from the planetary environment millions of years ago has to be dug up and reintroduced to the environment. Not using a CO2 canister does, indeed, reduce your carbon foot print. It may not reduce it much but it is a reduction.
Let's also not forget...or you may not know...that CO2 is much more permeable than air in a bicycle tire. It's an emergency fix only. The rate of diffusion is influenced by the internal pressure but, generally speaking, a CO2 filled tire will be flat in 12 to 24 hours.
Finally, you need to reread that chart. That 7.5 (lb/ft3) x 10-2. In other words, a cubic foot of dry air at sea level weighs about 0.075 pounds per cubic foot.
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