We are used to seeing the tried and trusted CO2 inflators, but harking back to old physics and chemistry lessons when I did gcse exams last year, I always wondered why nitrogen - a gas les dense (lighter) than air, and can be stored in gas cylinders - has never been used in bicycle tyres.

I would even consider it an upgrade to using air from a hand/track pump, and car giant Nissan pioneered the use of nitrogen in the 'GT-R' sports car's tyres to aid traction; they considered regular air to be 'too unstable' for the dependence on the cars tyres.

Not only this, but I recall carbon dioxide (CO2) deing much more dense (heavier) than air, and that it 'flows' rather than 'floats' as with nitrogen . Carbon dioxide molecules under pressure, can just about squeeze through rubber molecules, whereas nitrogen molecules are much larger, so pressure loss is considerably lowered.

Last of all, making up 78% of air (and rising), nitrogen is an almost infinite resource, so why not use it for the billions of bicycles and cars we have on this wretched planet? I believe there is money in this, somebody please make one!

CO2 can be extracted from ait at much higher temperatures than nitrogen. To get Nitrogen out of air you have to cool to -196 celcius. That's expensive. CO2 is cheaper that why it is found in portable cartridges.

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viewtopic.php?f=10&t=111416" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Hi,

Ah, someone beat me to it.

Still, here goes:

http://velonews.competitor.com/2010/10/news/cyclocross/technical-faq-with-lennard-zinn-blowing-up-tires_146989



Air already consists of roughly 78% of Nitrogen.

Ciao,

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Reason for using Nitrogen in car tires which is becoming more common now a days is the stability. It contains no oxygen and no moisture so it is not susceptible to temperature change.
Effectively your tires do not get low on pressure when the temperature outside drops. Pressure does not go up when the tire heats up.

This is very simple. Buy a nitrogen regulator and go to a welding supply palce and get yourself a tank of Nitrogen. Probably cost you $20 for the gas (tank is probably 100 though).

Also the above link to that setup sucks. Get a real nitrogen regulator like for a kegerator so you have a high pressure gauge and a low. You can adjust this to what ever pressure you want.
FYI a full tank comes in at 2200 psi so it will last you quite a while probably years.

this remind me of this:
http://www.stayfill.com/

"Stay harder, longer"
Straight from the top of the stay-fill website.

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Question:

If a tube is filled with Nitrogen (as opposed to regular air mix) and is used in Carbon Clinchers (CC) on a descent where there is a risk of over heating the rim, would the tube be less likely to blow out?

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Exp001

Sorry, the scientist in me has to call bullsh!t on this one.

Ideal gas law applies to nitrogen molecules (N2) too.

PV=NRT.

Cheers

I think the "added stability" is form the dryness of the nitrogen compared to air, when you cool air down the water condenses, so on a really cold day there might be some condensation in the tubes.

But CO2 from cylinders are dry too.



CO2 is a much, much bigger molecule than nitrogen, C O and N atoms are all comparably sized, theres 3 in a CO2 moelcule and 2 in an N2 molecule. That's why nitrogen is lighter for a given number of moles. Loseing pressure is due to the thin sidewalls of raceing bike tyres/tubes, air is 78% N2, if tyres weren't porous to it they wouldn't be porous to air, either that or your tyres would end up full of pure nitrogen as everythign else seeped out, which doesnt happen!



You can get them, you can also get laughing gas (N2O, nitrous oxide) in the same cannisters, mainly because all three are mostly inert and the main use of those tyre inflator cannisters is acutaly in food preperation (N2O is used for make wipped cream), look at the domain registrtion for tyreinflators.co.uk, it's owned by a catering supplies company.

CO2 is cheep as it's an industrial waste product, nitrogen costs a bit more (not much, at the quantities were talking the bottling/transport probably costs 10x, 100x or even 1000s x what the gas does) as it has more uses and has to be extracted from air.

Back of a fag packet calc says a 23mm x 700mm tyre inflated to 100psi would weigh about
11g with CO2
7g with N2
8g with Air

Doesn't happen? Not according to this bloke. O2 and N2 molecules are more or less peanut shaped. O2 has a smaller small dimension than N2 because O2 has 2 more protons constraining its electron cloud.

Dr. Keith Murphy explains it thus:
http://www.getnitrogen.org/pdf/graham.pdf" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

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I'm not convinced, I suspect the answer is contained in the first few paragaphs of that link. The major factor in pressure loss is effusion not permeation (IMO). My evidence would be that a thin thube (70g michelin) loses it's pressure over 3-4days. A 150g tube loses it over wayyyyyy more than double that, they might feel soft at the end of the month? Which would imply that there are pores in the tube, the thicker the tube the more likely these pores are to end in a dead end. If the process was permetive then mas transfer would be proportional to the thickness of the tube, and it's not. Whereas a series of random pores would give an exponential decreace in mass transfer with increaced thickness, which seems to be closer to what we observe.

Also if the gas in the tyres was slowly increacing in nitrogen concentration each time it needed pumping up to replace the lost oxygen then we'd see then needing pumping up very quickly after fitting, then longer and longer intervals between top ups as the concentration approaches 100% N2. IME this doesn't happen, they always need pumping up.

I have noticed that tyres seem to hold their air better the longer they have been inflated. It is more noticeable in heavy tubes than light ones.
Actually I will try to check this. I have latex, tubeless and 55g butyl tubes. I'll have to get a pressure gauge.

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In that case that shows that in the thick tube the process is permative assuming that my hypothesis was corect that doubleing the thickness would halve the mass transfer by permeation but exponentialy reduce it by effusion. Whilst in the thin tube the effusion is exponentialy faster than it was in the thick tube whilst permeation has only doubled.

Worth doing to save 1g? A 16g CO2 cylinder costs about 50p, if N2 cost the same then it'd be 50p/gram lost compared to air from a track pump.

Anyone got 3 spare wheels, 3 identical tyres, rim tapes and a variety of tube thicknesses to hand?

My understanding is that one reason nitrogen is used in car race tyres and in aircraft tyres is because it is a cheap way to eliminate oxygen from the tube and replace it with an inert gas. If the tyre overheats and explodes then sparks won't ignite the nitrogen - so no fire. I don't believe we generate enough heat in our bike tyres for that to be a problem.