Bicycle Mechanics - Nitrogen inflated tires - cheaper than CO2 and keeps rims cooler under braking?

Hi,

I've been looking a bit into CO2 pumps, but also into using nitrogen (or rather, nitros oxide) to inflate the tires.

I've done some searching here and on the Internet about using nitrogen. Most people say it doesn't matter much, and I'd probably generally agree. However a few things about nitrogen don't seem to be mentioned when people have discussed using it with bicycle tires.

Firstly, I can get unthreaded N20 cartridges cheaper than unthreaded CO2 ones:

http://finewhip.cart.net.au/store/nitrous-oxide-medical-grade-16g-finewhip-chargers-1-box-5-charge.html - $1.41 each

vs

http://finewhip.cart.net.au/store/co2-un-threaded-cartridge-16g-x-10.html - $1.69 each

(both exceptionally cheap when you compare them with bike/tool company branded ones)

I'm thinking of buying a Topeak One Timer pump, which can take both threaded and unthreaded cartridges, so I think it'll fit the unthreaded N2O cartridges above.

Secondly, apparently nitrogen is less prone to expansion under heat than normal air is. I wonder if this would be beneficial under heavy braking when the rims heat up, and therefore reducing the chances of the tube popping. Roads can get pretty hot here in Adelaide in summer (greater than 38C/100F air temperature is common enough), so nitrogen in the tubes might help there as well.

Thirdly, with less oxygen in the tube, they might last a bit longer, although it's probably negligable enough that it's not a major advantage.

Finally, there doesn't seem to be any comments about whether nitrogen suffers from the fairly rapid deflation that CO2 seems to.

It looks like it's cheaper to use N2O, so I might have a go with using it anyway. However I thought I'd also see what people thought here.

Waste of money. Do you ever use a floor pump? If so, you will be contaminating your tubes as soon as you do. And what is cheaper than using a floor pump?

Nitrogen is used in auto racing because it is more stable then ambient air and contains no water vapor. Us cyclists don't come near the conditions that tires in auto racing have to deal with.

We may have to go to carrying nitrogen cartridges instead of CO2 since the Obama administration's EPA will declare CO2 a poison and ban the use and emission of it.

Nitrous oxide is no laughing matter......ha! ha! ha! ha!

Don't confuse nitrogen with nitrous oxide. Nitrogen (N2) is a very stable, but nitrous is an oxidizer (NOS).

Where does the heat come from under braking? And how is that related to what's inside the tyre?

Nitrogen is used in auto racing because it is more stable then ambient air and contains no water vapor. Us cyclists don't come near the conditions that tires in auto racing have to deal with.

We may have to go to carrying nitrogen cartridges instead of CO2 since the Obama administration's EPA will declare CO2 a poison and ban the use and emission of it.

everyone will get small explosive cartridges instead, sounds like a great idea :lol:

The OP is talking about nitrous oxide from restaurant supply distributors.

What kind of pressure will the NOS cartridge put in your bike tire? I don't think the seller means for those to be used in a bike tire.

Unthreaded 12g co2 cartridges are cheaper. You can buy a box of 25 at Walmart for about 50 cents a pop.

I think Nitrogen will only be of use in cooling if you intend to travel at Mach 3.0 or faster. you only benifit might be the .20$ you save per cartridge which half of that will be lost in shipping.

Secondly, apparently nitrogen is less prone to expansion under heat than normal air is. I wonder if this would be beneficial under heavy braking when the rims heat up, and therefore reducing the chances of the tube popping. Roads can get pretty hot here in Adelaide in summer (greater than 38C/100F air temperature is common enough), so nitrogen in the tubes might help there as well.

Totally untrue. PV = nRT is true for all ALL gases. In this case, n and R are constant for a given volume of gas in a tire, so you get (PV)/T = constant. Basically, all gases expand and contract at the same rate relative to a given change in temperature.

The OP is talking about nitrous oxide from restaurant supply distributors.

Yes, medical grade nitrous oxide from a restaurant supply distributor.

Totally untrue. PV = nRT is true for all ALL gases. In this case, n and R are constant for a given volume of gas in a tire, so you get (PV)/T = constant. Basically, all gases expand and contract at the same rate relative to a given change in temperature.

well, given the fixed volume of the tire fully inflated the n (number) of mols of the gas in qestion will be different because they have different molecular weights, so their expansion will be different

Waste of money. Do you ever use a floor pump? If so, you will be contaminating your tubes as soon as you do. And what is cheaper than using a floor pump?

Not much, but they're a bit heavy to take with you riding ;)

Totally untrue. PV = nRT is true for all ALL gases. In this case, n and R are constant for a given volume of gas in a tire, so you get (PV)/T = constant. Basically, all gases expand and contract at the same rate relative to a given change in temperature.

That's the Ideal Gas Law which is good for monoatomic gases.

Also you neglected n, which is number of moles. For N2O, MW=44 so 16g is 16/44=.36 moles. For N2 mw=28 so 16g is 16/28=.57 moles.

As a bit more background, here's my thinking.

I've only recently got a road bike, so I'm now getting used to pumping my tires up to 100PSI, rather than 40 to 50 odd PSI on my mountain bike. I do have a floor pump. I also have a micropump which I carry on my bike, but after considering the effort I have to go to when I use my floor pump to get to 100PSI, I'm starting to wonder if the effort to do it with a micropump out on the road would be worth it - hence I'm thinking about the CO2 pump as option for on the road. If using NO2 is slightly cheaper, and has some, possibly minor advantages over CO2 e.g. doesn't quickly deflate, then I thought it might be worth considering.

Where does the heat come from under braking? And how is that related to what's inside the tyre?

From the friction of the brake pads on the rim. From memory, there is a warning in the book, "Bicycling Science", 3rd edition, that under a lot of heavy braking e.g. going down a long steep hill, the rims can heat up enough that they could cause the tube to weaken i.e. melt and deflate a.k.a. pop. This hill is one where I'm wary of that issue - there are a couple of nasty hair pins on it that if you missed them because your tire blew out, you're either launched off the side of the hill, or into a hill face :

http://maps.google.com.au/maps?f=q&source=s_q&hl=en&geocode=&q=mt+osmond,+adelaide&sll=-25.335448,135.745076&sspn=56.971931,88.330078&ie=UTF8&hq=&hnear=Mount+Osmond+South+Australia&ll=-34.95905,138.66644&spn=0.00328,0.005391&t=h&z=18&layer=c&cbll=-34.959112,138.666363&panoid=nesd1DZg00hpgVjW-b8_bg&cbp=12,15.07,,0,5

Where does the heat come from under braking? And how is that related to what's inside the tyre?

The heat comes from the friction of the pads against the rims. (On cars from the pads agains the rotors.) So the rim heats up, which heats the gas in the tube.

I think the idea is that air (79% N2, 20.9 % O2) has some water vapor, which absorbs more heat than nitrogen which can be drier. This leads to more expansion and contraction. I've also read that pure nitrogen (N2) is less likely to leak out that air because of the size of the N2 molecule. I don't know if that's true.

I do have N2 in my car tires and I will say that it seems that the tires remain inflated longer with N2. Despite the fact that air is 79% N2.

From the friction of the brake pads on the rim. From memory, there is a warning in the book, "Bicycling Science", 3rd edition, that under a lot of heavy braking e.g. going down a long steep hill, the rims can heat up enough that they could cause the tube to weaken i.e. melt and deflate a.k.a. pop...

Or melt the glue enough that a tubular will slip off the rim.

Nitrogen explosive? Since when? Like any other gas under compression, you can have explosive decompression of the container, but nitrogen isn't flammable or combustible.

Nitrogen explosive? Since when? Like any other gas under compression, you can have explosive decompression of the container, but nitrogen isn't flammable or combustible.

It's N20 (http://en.wikipedia.org/wiki/Nitrous_oxide)

Nitrous oxide can also be used in a monopropellant rocket. In the presence of a heated catalyst, N2O will decompose exothermically into nitrogen and oxygen, at a temperature of approximately 1300 °C. Because of the large heat release the catalytic action rapidly becomes secondary as thermal autodecomposition becomes dominant.

i thought the benefit of co2 was that it is bottled as part liquid and as it expands to gas it allows sufficent pressures in a bike tire. compressed air on the other hand would need much much higher pressure and volume in order to fill a bike tire. i do not think that can get a bike tire to 100 psi.

I use a good floor pump at home, and CO2 on the road (with a mini-pump along for the ride as backup, if I run out of cartridges).

My floor pump is good. Not too much effort to pump to 100 psi. If yours is too much effort, try a better one. I think mine cost $40 or something.

CO2 cartridges are cheap, if you buy them by the box. In the US, that ends up meaning US$13-15 for a box of 25, at a discount store (like WalMart) or a hunting store. It might be different in Australia.

If you find yourself using so many cartridges that the cost is getting to be uncomfortable, then maybe you're using them when you could be using your floor pump?

On the other hand, there are some good frame pumps these days. People seem to like the Topeak Road Morph. It's reputed to be almost as good as a floor pump. When I use up all 25 of my CO2 cartridges (which should take me a couple years), I might go out and buy one, to see if it's as good as people say.

And on the subject of NO2, see:
Why not nitrogen instead of CO2? (http://www.bikeforums.net/showthread.php?587947-Why-not-nitrogen-instead-of-CO2&highlight=no2)

Nitrous oxide is also known as laughing gas as a prior poster indicated. It can be used as an engine horsepower booster and liquefies at relatively low pressure, like CO2. If it contacts the wrong contaminant it can break down in a highly exothermic reaction. It is also classified as a much more effective hot house gas than CO2 and is apparently a ozone destroying gas so is not particularly environmentally friendly. It is also listed as a strong oxidizer so might speed up tube deterioration.

The instability risk and the environmental concerns make it a poor choice for tire inflation IMO. Here is a link to the Wikipedia article on it.

http://en.wikipedia.org/wiki/Nitrous_oxide

There is a clear consensus that CO2 causes Mann made tire warming.
I usually use a 70% mixture of nitrogen and whatever else is in the atmosphere.

That's the Ideal Gas Law which is good for monoatomic gases.

Also you neglected n, which is number of moles. For N2O, MW=44 so 16g is 16/44=.36 moles. For N2 mw=28 so 16g is 16/28=.57 moles.


well, given the fixed volume of the tire fully inflated the n (number) of mols of the gas in qestion will be different because they have different molecular weights, so their expansion will be different

No. n, the number of moles of gas, will be the same, whether inflating with air, helium, carbon dioxide, nitrogen, or nitrous oxide. There will be different masses of each substance in proportion to the formula/molecular weights. Only at relatively higher pressures and/or at temps where liquefaction occurs do any of these gases depart from ideal behavior.

N2O and CO2 are liquids at ambient temperatures and at pressures low enough that they can be held as liquids in cylinders and little cartridges (roughly 1000 psi). This allows a large number of tire inflations worth of gas to be stored in the little cartridge. Couldn't do that with air or N2, which don't liquefy until at very high pressures.

The heat capacities and thermal conductivities differ between the gases. Most of the heat capacity is in the solid components -- rim, tire, and tube -- I will guess there's no practical effect due to different gases.

n2o and co2 are liquids at ambient temperatures and high enough pressures (several hundred psi)...

fify.

No. n, the number of moles of gas, will be the same, whether inflating with air, helium, carbon dioxide, nitrogen, or nitrous oxide. There will be different masses of each substance in proportion to the formula/molecular weights. Only at relatively higher temperatures and/or pressures do any of these gases depart from ideal behavior.

N2O and CO2 are liquids at ambient temperatures and low enough pressures (several hundred psi) that they can be stored as liquids in cylinders and little cartridges. This allows a large number of tire inflations worth of gas to be stored in the little cartridge. Couldn't do that with air or N2, which don't liquefy until at very high pressures.I think you're talking about 1000psi for CO2 and 3000psi+ for N2.

n.m.

how about xenon, will that stay inflated longer?

how about xenon, will that stay inflated longer?

I'd try Krypton first.

There is a clear consensus that CO2 causes Mann made tire warming.
I usually use a 70% mixture of nitrogen and whatever else is in the atmosphere.

This.

Seems everyone forgets that the air we breathe is 70% nitrogen. Why pay for an additional 30%?

My science books said that air is about 79% nitrogen and 19% oxygen with the rest being a multitude of other gases. So a regular pump or compressor is moving mostly nitrogen anyway. There is a lot of hype about using nitrogen in tires, but IMHO it is mostly just hype with no measureable real-world advantage or difference.

i use halogen

I believe that bottled nitrogen is used by industry and in race car tires because it is inert and dry. Neither quality is important for bike tires.

Topeak has several bicycle pumps that 'morph' into a mini-floor pump.
As far as heating up tubes in 100+ degree weather and exploding, we live in the desert in Arizona. Have bicycled in 117 degrees and many times in 100+ (up to 90 days a year). Have lived/cycled in the desert for 31 years, no blown tires due to heat buildup.
We use a Topeak Mt.Morph': 100 pump strokes gets in 100 lbs of air into a 700x25c tire. In the long run, cheaper than any type of inflator and more eco-friendly.