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I am completely new to riding bikes and know that are usually filled with air but nowadays some people fill them with Nitrogen instead.

I don't know why they prefer to fill their tires with nitrogen as it is more costly than filling them with air.

What are the benefits of filling tires with Nitrogen?

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@NeilFein The question was how and my question is why? –  SpringLearner Dec 17 '13 at 7:53
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The advantage of Nitrogen - your bike accelerates faster and has reduced rolling resistance.... because your wallet is so much lighter....... –  mattnz Dec 17 '13 at 8:45
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The advantage is that it makes money for the guy who sells the nitrogen. It also give stupid rich guys something to brag about, when they bore of talking about their carbon frame, et al. –  Daniel R Hicks Dec 17 '13 at 12:02
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Here's the Straight Dope. The biggest advantage is less chance of fire if your brakes overheat going downhill. –  Daniel R Hicks Dec 17 '13 at 17:21
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I only fill with helium. Lightest gas there is! Reduces my bikes weight by 10g too! –  RoboKaren Jun 19 at 3:21

6 Answers 6

There are some compelling reasons for filling vehicle tires with pure nitrogen in performance situations, but for bike tires it's just snake oil. There aren't substantial enough temperature fluctuations in a bike tire to justify the pressure consistency argument.

It's also worth noting that the air you breathe and fill your tires with is more than three-quarters Nitrogen, so this isn't as special as it may sound.

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more than 3/4 nitrogen, unless things are very different up there in the northern hemisphere. 78% nitrogen, roughly. –  Mσᶎ Dec 17 '13 at 20:39
    
@Ӎσᶎ - There's a higher proportion of hot air the closer you get to Washington. –  Daniel R Hicks Dec 17 '13 at 21:24
    
I looked for a paper on the change in nitrogen concentration with average air temperature but couldn't find one. Do you have a reference? –  Mσᶎ Dec 17 '13 at 21:53
    
@Ӎσᶎ d'oh! Yup misremembered on my percentages. Will edit. –  joelmdev Dec 17 '13 at 22:05
    
@Ӎσᶎ that was certainly a joke from DanielRHicks –  joelmdev Dec 17 '13 at 22:06

There are several advantages, most of which apply only marginally to bicycles. A nitrogen seller lists all of them, other sites list pros and cons. The key thing is that it's not about adding nitrogen so much as reducing oxygen, water and other gases.

  1. Nitrogen molecules are larger than water, oxygen and most others, so they percolate through tyres more slowly. This means tyres stay at a usable pressure longer. This is the main benefit that a cyclist will see.

  2. Nitrogen changes pressure with temperature slightly less than water does. But bicycle tyres stay close to ambient temperature almost always.

  3. Nitrogen is less reactive than oxygen, so your tubes will last a little longer. But since tubes normally fail due to punctures rather than oxygen embrittlement it's going to be tricky to measure.

Note that the nitrogen in a bicycle tube will not be in contact with the rim, so the silly motorist argument about less rim corrosion doesn't apply to bicycles at all. In compensation bicycles get a much simpler change-over: just deflate the tube, squeeze all the air out of it, then inflate it with nitrogen. No need for repeated inflate-purge cycles.

But remember that the difference is only in the 20% of the molecules that you've changed from "other" to nitrogen, 80% are nitrogen in both cases.

Also, due to the difference in percolation rates, over time the air in your tyres will slowly become more nitrogen-rich (the other gases percolate out faster than the nitrogen). If you get no punctures, after a few years your tyre might contain over 80% nitrogen!

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On the morning of triathlon competition, when sun comes up and air became hotter, you'll hear blowing tire every several minutes over racks with couple thousand bikes. So, if you don't want surprise in the race day, you can use dry nitrogen or even dry air for tires.

Last year my tire blew up on the hot intersection on red light also.

I don't think if there any performance advantage using it.

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That is almost surely the result of incompetent maintenance on behalf of the triathletes. I've pumped my tires up to max for my tires (120psi) outside in -20F weather, ridden around, then brought my bike inside, resulting in nearly a 100 degree temperature swing, without any sort of problems. –  whatsisname Jun 19 at 16:54
    
The blown tire in the heat is due to uneven heating & resulting uneven expansion of the tire. –  Daniel R Hicks Jun 20 at 22:35

The biggest advantage to filling your tires with Nitrogen is consistency.

Air pressure fluctuates based on temperature, whereas Nitrogen fluctuates to a much much lower degree. http://www.popularmechanics.com/cars/how-to/repair-questions/4302788 While this article is talking about car tires, the principle is the same. People who ride competitively can have an advantage with Nitrogen simply because the pressure is always where they want it. Also, if you ride your bike a lot in many different weather conditions, Nitrogen can save you money in the long run since your tires wear slower (assuming you always keep the tires at the ideal pressure).

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You'd have a hard time convincing me that any of that was "significant" -- that the effects were even measurable. And even if you do manage to reduce tire wear slightly you can buy a lot of tires for the $1000+ that a nitrogen generator costs, or the $10 a pop service stations charge. –  Daniel R Hicks Dec 17 '13 at 17:20
    
Yeah, that's a pretty hard sell considering that the earth's atmosphere is already 78% nitrogen. You're much better off filling your tires to the proper pressure before each ride vs. having the incorrect pressure of nitrogen because of the time and cost constraints of going to the service center every time you want to top up your tires. –  Kibbee Dec 17 '13 at 17:49
    
@Blam: That example will be useful when I fill my tires up with water and go riding inside the crater of an erupting volcano. Until then, that comparison is just silly. –  whatsisname Jun 19 at 16:49

Absolutely none. Filling tyres with nitrogen matters in Formula One car, not in bicycle. In bicycle, difference between air and nitrogen filled tyres is hardly measurable. All advantages of nitrogen in bicycle tyres are no more than placebo.

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what is the reason for filling with nitogen in formula one car –  SpringLearner Jun 20 at 11:40
    
@SpringLearner - It gives them something like a 0.5% edge in rolling resistance. Which will win a F1 race, but won't get you where you're going even 1 second faster. –  Daniel R Hicks Jun 20 at 22:32
    
More than that, at formula 1 heat levels it behaves more predictably than regular air. –  Batman Jun 21 at 1:39

Not going to delete to lose the down votes.
The stated question is advantage is nitrogen. Not should I use nitrogen. I cover the technical side of the characteristics of nitrogen versus air and the chemical and physical reason for the differences.

  1. A nitrogen molecule is larger than oxygen so it does not leak as easily/rapidly.
    Nitrogen is actually a little lighter than oxygen and an nitrogen atom is smaller. In air they both occur as molecules of two atoms. The they way the hold hands is different so N₂ is slightly bigger then O₂. http://www.getnitrogen.org/pdf/graham.pdf

    O2 "permeates" approximately 3-4 times faster than does N2 through a typical rubber.

  2. Stable and non-reactive.
    Oxygen, nitrogen, are water are all relatively stable and non-reactive.
    Oxygen is a stronger oxidizing agent. Nitrogen oxidizes the rubber at a lower rate.
  3. Better PVT characteristics. Nitrogen does not change pressure with temperature as much as air. You don't want the pressure in your tires to change.
  4. Storage and transportation
    There are some of rent a bike racks the use nitrogen because it is easier to get a storage and transportation permit. Oxygen alone is not combustible but it supports combustion. Nitrogen is not combustible does not support combustion.
Why nitrogen versus an inert gas such as Argon?
Nitrogen exists as a molecule N₂ and is nearly as stable as an inert gas. It is used because it is available. Nitrogen is a byproduct of liquefaction and fractional distillation of air to produce oxygen. Nitrogen is not an inert gas but a nitrogen molecule N₂ is very stable. It is a relatively cheap dry stable (non reactive) gas. And does not easily liquefy (boiling point of -320 F).

Why does Nitrogen have better PVT characteristics?

In the operating range of a tire oxygen and nitrogen have the same PVT characteristics. They are both ideal gasses. Ideal in that they don't liquefy and have neither attractive nor repulsive forces. They are neutral.

A bicycle does not generate enough friction to change the temperature much. Bicycle will be pretty close to ambient temperature. If you start a ride in the AM you may get a 10 Celsius swing by 2 PM.

Relative to the ideal gas law, PV = NRT, oxygen and nitrogen have the same behavior. T is absolute in that equation. 0 Celsius is 272 Kelvin (absolute). 10 to 20 Celsius is a difference of 4% in pressure. So if the tire started at 100 PSI the pressure when to 104 PSI.

Water is the PVT problem. Water is not an ideal gas. In the operating range of a tire H₂0 can exist as a gas and a liquid. From the liquid state to gas state the volume change is over 100 (this is how you can inflate a tire with a little CO₂ cartridge).

In the range of 10 Celsius versus 20 Celsius the vapor pressure of H₂0 nearly doubles at atmospheric pressure.
Vapour pressure of water

Over that same 10 Celsius swing what is the pressure change of water. The vapor pressure of water doubles. Where the ideal gas (N₂) changes 4% water changes 100%. In that same range the water pressure goes up 1 PSI. So the total PSI is 105. At only 1% composition water contribute 25% of the pressure change. The statement from Moz that Nitrogen changes pressure with temperature slightly less than water does is not correct. The difference is 40X but at only 1% that 40X is still not much of a total contribution.

So a 1% pressure difference in 10 centigrade. Racers will go after grams. 1% may matter to them. It is not clear if racers users nitrogen (in tires). I see sellers stating it is used by races but I don't see and races saying they use nitrogen.

Nitrogen is used in altitude tents to reduce the O₂ content. This stimulates the production of red blood cells. So racers may use tires as an excuse for nitrogen tanks.

From 0 to 100 Celsius the vapor pressure of H₂0 goes from 611 to 101417 Pa. In that operating range H₂0 is over 100 times more sensitive to temperature than nitrogen or oxygen relative to pressure. So for a race car the change is noticeable.

Why CO₂ in those portable canisters and not nitrogen?
CO₂ compresses to liquid state at a lower pressure then nitrogen. The boiling point of CO₂ is -56 Celsius. Can use CO₂ to inflate a tire and not risk it going back to a liquid state in the operating range of a tire.

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Can you actually run the numbers for us please? Given two tyres, one filled with air at typical compressor output composition and one with nitrogen, what is the actual difference in pressure as the temperature changes from, say, 5°C to 35°C, and how does that change rolling resistance? Your answer doesn't seem to actually get to the affect on bicycle performance that the question is asking for. –  Mσᶎ Jun 19 at 4:03
    
@Mσᶎ The question is why nitrogen? Your answer does not quantify difference in rolling resistance nor quantify the difference in percolate. You state "Nitrogen changes pressure with temperature slightly less than water does" without explanation. The question is why nitrogen instead of air? One of the reasons is water. And I explain why the water is bad. –  Blam Jun 19 at 14:15
    
@Mσᶎ Like your web site you have done some cool projects. –  Blam Jun 19 at 14:30
    
You toss out a lot of numbers but nowhere do I see how those numbers translate to a practical advantage that would justify the time and cost of using nitrogen. Slower leakage is nice, but really, it takes me 60 seconds to top off a tire. Rubber in tubes oxidizing has never been an issue for anyone except old bikes that have been sitting in storage. So all that's left is less change with temperature fluctuations, but you haven't shown how the difference is significant enough to matter. –  Carey Gregory Jun 19 at 14:38
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If you can't demonstrate a tangible benefit then I don't think you've answered the question. It sounds like you're saying your answer is actually a comment on Moz's answer rather than an answer itself. –  Carey Gregory Jun 19 at 19:27

protected by Gary.Ray Dec 17 '13 at 17:58

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