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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 08-13-08, 04:45 PM   #1
ajbeck21
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dry nitrogen

anyone use dry nitrogen in there tires if so what are the benefits
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Old 08-13-08, 05:04 PM   #2
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There are minimal benefits in car, truck and semi tires. I am pretty sure it would be even less advantageous for bicycle tires.
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Old 08-13-08, 05:07 PM   #3
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air is mostly nitrogen, it's really the dry part that makes it valuable. Dry nitrogen is really cheap, I get a large tank for $4 a month -- don't use it for bike tires though. It makes sense for race cars, and it might make sense for cars that are driven at speed because the pressure goes up more with atmospheric air than dry nitrogen. For example, if you like to run high pressures for gas savings, dry nitrogen makes sense, because you are much less likely to over-pressure your tires. OTOH, it's incredibly overpriced if you don't get it from the gas supply.
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Old 08-13-08, 05:08 PM   #4
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anyone use dry nitrogen in there tires if so what are the benefits
You get to pay someone for something you can get for free. Bike tubes have a huge surface area for their tiny volume. Even if you halved the rate of pressure loss, you'd still lose lots, and have to refill the tires on a regular basis. Non of the other alleged benefits ot using nitrogen in tires matter on a bike. Tubes simply don't die of oxidation failure; I've got a 20-odd year old tube in one of my bike wheels. The bike it's on sat for ages and ages; the tires died of old age and neglect. The tubes, on the other hand, were fine.
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Old 08-13-08, 05:33 PM   #5
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I've been wondering about the answers to this. Its been a long day and I don't feel like doing the chemistry, but I'm sure the weight-weenies can argue that at an atomic weight of 28, equal volumes of N2 and Air would show N2 being lighter, although compressibility issues could easily show taht to get 120psi the N2 comes up heavier...

That said, one flat and you'd be on an N2/CO2 or N2/Air mix...not to mention you've got to purge your tires prior to filling and all that.
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Old 08-13-08, 06:11 PM   #6
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I've been wondering about the answers to this. Its been a long day and I don't feel like doing the chemistry, but I'm sure the weight-weenies can argue that at an atomic weight of 28, equal volumes of N2 and Air would show N2 being lighter, although compressibility issues could easily show taht to get 120psi the N2 comes up heavier...

That said, one flat and you'd be on an N2/CO2 or N2/Air mix...not to mention you've got to purge your tires prior to filling and all that.
Well, it's not much work. PV = nRT, right? We know the pressure, let's call it 120 psi. that's 120 psi gauge, so absolute pressure is about 135 psi, so about 931 kilopascals. A tire is a torus, right, so its volume is 2 pi^2 Rr^2, where pi is pi, r is the radius of the circle being rotated, and R is the radius about which it's rotated. We'll use a 700cX28 tire, because that's a likey size to be at 120psi. 700c tires are 622 mm in diameter, so R is 0.622m/2 + 0.028m/2 = 0.325m. r is 0.028m/2 = 0.014 m. so the volume works out to 2 * pi^2 * 0.325 * 0.014^2 = 0.00126 m^3, or 1.26 liters. As we said earlier, PV = nRT. We'll call T 300 K, which is 27 C, or about 80some F. we're solving for n, so we've got
PV/RT = n. which is (931*1.26)/(8.314 * 300) = 0.47 moles. So N2 to fill the tire would weight about 14 g. Plain air, dry, has a molecular weight of 29. So, the savings are (29 * 0.47) - (28 *0.47) or 0.47 grams. Somehow, I doubt you'll notice.
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Old 08-13-08, 07:07 PM   #7
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Well, it's not much work. PV = nRT, right?
That's the ideal gas law, and it holds to the extent that the real gases involved approximate "ideal".

I think that the real advantage of dry nitrogen, such as it is, is that nitrogen is nearly inert, and there's no oxygen and no water to degrade the rubber of the tube. So your tubes will last longer...theoretically.
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Old 08-13-08, 07:51 PM   #8
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Enough said it's useless to us on bikes I use it on a daily bases in the air conditioning world so I was just curious.
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Old 08-14-08, 07:25 AM   #9
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That's the ideal gas law, and it holds to the extent that the real gases involved approximate "ideal".

I think that the real advantage of dry nitrogen, such as it is, is that nitrogen is nearly inert, and there's no oxygen and no water to degrade the rubber of the tube. So your tubes will last longer...theoretically.
At the temperatures and pressures in bike tires, gases work very much like ideal gases.
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Old 08-15-08, 02:06 PM   #10
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Well, it's not much work. PV = nRT, right? We know the pressure, let's call it 120 psi. that's 120 psi gauge, so absolute pressure is about 135 psi, so about 931 kilopascals. A tire is a torus, right, so its volume is 2 pi^2 Rr^2, where pi is pi, r is the radius of the circle being rotated, and R is the radius about which it's rotated. We'll use a 700cX28 tire, because that's a likey size to be at 120psi. 700c tires are 622 mm in diameter, so R is 0.622m/2 + 0.028m/2 = 0.325m. r is 0.028m/2 = 0.014 m. so the volume works out to 2 * pi^2 * 0.325 * 0.014^2 = 0.00126 m^3, or 1.26 liters. As we said earlier, PV = nRT. We'll call T 300 K, which is 27 C, or about 80some F. we're solving for n, so we've got
PV/RT = n. which is (931*1.26)/(8.314 * 300) = 0.47 moles. So N2 to fill the tire would weight about 14 g. Plain air, dry, has a molecular weight of 29. So, the savings are (29 * 0.47) - (28 *0.47) or 0.47 grams. Somehow, I doubt you'll notice.


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Old 08-16-08, 06:20 PM   #11
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Old 08-16-08, 09:40 PM   #12
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Old 08-17-08, 05:55 AM   #13
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Well, it's not much work. PV = nRT, right? We know the pressure, let's call it 120 psi. that's 120 psi gauge, so absolute pressure is about 135 psi, so about 931 kilopascals. A tire is a torus, right, so its volume is 2 pi^2 Rr^2, where pi is pi, r is the radius of the circle being rotated, and R is the radius about which it's rotated. We'll use a 700cX28 tire, because that's a likey size to be at 120psi. 700c tires are 622 mm in diameter, so R is 0.622m/2 + 0.028m/2 = 0.325m. r is 0.028m/2 = 0.014 m. so the volume works out to 2 * pi^2 * 0.325 * 0.014^2 = 0.00126 m^3, or 1.26 liters. As we said earlier, PV = nRT. We'll call T 300 K, which is 27 C, or about 80some F. we're solving for n, so we've got
PV/RT = n. which is (931*1.26)/(8.314 * 300) = 0.47 moles. So N2 to fill the tire would weight about 14 g. Plain air, dry, has a molecular weight of 29. So, the savings are (29 * 0.47) - (28 *0.47) or 0.47 grams. Somehow, I doubt you'll notice.

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