CrashVector

I have a nitrogen generator that I use to fill my car tires with compressed nitrogen. Before you guys get all wierd, I use compressed nitrogen for two reasons:

1) It doesnt contain moisture like compressed air, which can corrode rims
2) The pressure doesnt fluctuate with temperature as much as compressed air


I've seen the little compressed CO2 cartridges for filling bike tires, but CO2 pressure fluctuates a LOT with temp changes...moreso than regular compressed air. Have any of you seen small nitrogen containers for filling bike tires?

mx_599

no, sorry

cyccommute 

And you probably won't. CO2 can be compressed and liquified at room temperature without too much cylinder pressure. N2 can't. For N2 to be liquid, it has to be at cryogenic temperatures and held there. You could compress it and put it in a small cylinder like a CO2 cylinder but the pressure required for the volume to fill the tire would require a very heavy wall. It wouldn't be made of light weight aluminum that's for sure

Just use a pump. It still puts are that is almost all nitrogen in the tire.

By the way CrashVector, your nitrogen generator doesn't make nitrogen that is any drier than compressed air. It probably has a scrubber on it that removes the water. I've seen similar systems for provided dry air for instruments.

cryptid01

Just curious, how do you evacuate all the normal air and water vapor that's already in the tire when mounted but before inflation?

True, but you will never see those temperature (and therefore pressure) differences in an mtb tire - Nitrogen, CO2, or otherwise. Don't sweat it.

mx_599

you would have to fill and purge a few times until most would be gone.

cyccommute 

Don't most tubes come 'empty'? At least all the ones I've ever bought were

mx_599

probably

besides, any residual air mixture would be pretty negligible when compared to the pressurized pure gas.

WorldWind

This is a joke right?

Relevance of scale applies here. Yes its true N2 is almost inert…but truly, all of you that are having a problem with your wheels corroding from the inside please raise your hands. The only ones that have their hands up are running true Magnesium racing rims and every one else has steel that has been powder coated on the inside or alum alloy rimes that are anodized or plated.

The way you get high purity nitrogen is by fractional distillation of liquefied air.

In a bike tire, please.
On my Mtn bike I probably change the pressure four or five times per ride to optimize traction. On my road bike I let almost all the air out after every ride and then pump them up to 120 or so before every ride.

I call BS.

gwhunt23

A shop around here has nitrogen tanks for filling up tires. The elite racers get their tubes all pumped up with Nitrogen before big races. It reduces the weight by 35%.

cryptid01

Hahaha! Reduces the weight from what to what exactly?

Dannihilator

From probably like 1.9 down to 1.89.

Svr

I see you're trying to validate the myth that triathletes are brain dead from the sustained effort of their sport.

gwhunt23

Ahaha, I can relate!

I calculated the 35% difference based on the weight of 1 liter of air/nitrogen. I don't know what the actual weight savings in grams is though, 'cause then you'd have to get into pressure and stuffs.

cyccommute 

Actually, it would reduce the weight by just about the percentage that Svr says. By removing the 19.5% O2 that is in the air with N2 you would see a significant change in weight. Nitrogen weighs 28 grams per mole of gas while oxygen weighs 32 grams per mole. If we assume that each tire has the volume of one mole of gas at STP (22.4 L which is about right for a standard tire), then at 32 psi, each tire would have about 3 atmospheres of gas in them or roughly 3 moles of gas per tire for a total of 12 moles of gas. If the oxygen is replaced with nitrogen, then for 12 moles of gas you would save right around 48 grams for the whole car! Wow! But it would be roughly 35% lighter than regular air.

[Edit: I need to improve my reading comprehension. I thought that this was for a cars. For bikes, at 120 psi (9 atmospheres), the weight savings per tire would be significantly more in real terms if all things were equal. But a 23mm 700C tire only has a volume of around 250 ml (being very generous) so per set of tires the total volume is 500 ml or roughly 0.02 moles of gas. At 9 atm pressure, you would be looking at a whopping 0.72g of weight savings! I'm not sure if the most strident weight weinie would worry about that amount ]