Tyres inflated with CO2...

essex-commuter
essex-commuter Posts: 2,188
edited May 2012 in Commuting chat
deflate quicker than those inflated with air. *FACT.

I have read this before but I've just noticed that the rear tyre I inflated last week with CO2 has lost about 20-30psi, a tyre with normal air in it would take months to lose this much.

No question, just a comment!


*unless I have a slow!

Comments

  • mudcow007
    mudcow007 Posts: 3,861
    happens to mine too

    although my tyres lose air too if the bike is left for a few days
    Keeping it classy since '83
  • UndercoverElephant
    UndercoverElephant Posts: 5,796
    Absolutely true, the molecules are small enough to permeate through the rubber. You should always re-inflate the next morning.
    Sun - Rain - Snow
  • nameinuse
    nameinuse Posts: 71
    CO2 permeates faster through rubber than most other gasses - according to an utterly thrilling paper in the Journal of Membrane Science I just found, around 50 times as quickly as nitrogen (the main constituent of air) does. Makes me wonder why they don't fill those bulbs with nitrogen instead.

    Ah, Friday afternoons waiting for the computer to do something...
  • spasypaddy
    spasypaddy Posts: 5,180
    if i co2 my tyre i empty the tyre when i get home and reinflate with track pump
    BMC TM01 - FCN 0
    Look 695 (Geared) - FCN 1
    Bowman Palace:R - FCN 1
    Cannondale CAAD 9 - FCN 2
    Premier (CX) - FCN 6
    Premier (fixed/SS) - FCN3
  • madtam
    madtam Posts: 141
    Some car tyre places charge a premium to inflate with nitrogen because it doesn't permeate out as fast so the tyre stays up longer.


    Anyone want to comment on using Helium or Hydrogen in tyres to reduce weight ?? :mrgreen:
  • tgotb
    tgotb Posts: 4,714
    madtam wrote:
    Anyone want to comment on using Helium or Hydrogen in tyres to reduce weight ?? :mrgreen:
    Probably quite hard to keep it in for any decent period of time (and the weight savings, if you work them out, are tiny).

    I believe NASA used nitrogen for the space shuttle's tyres...

    EDIT: 'cos I'm bored, I just worked it out. The air in a single 21x700c tyre inflated to 100psi weighs around 4g. Can't be bothered to work it out for Helium, but it's clearly more than 0g. You'll gain more by having a haircut...
    Pannier, 120rpm.
  • SimonAH
    SimonAH Posts: 3,730
    A lot of race cars inflate with N2 as well.

    I used to spend a lot of time on a Mini (classic) forum when I was building my last one and there was a monstrous long thread where some of the guys were explaining why they filled their tyres with N2 and the huge perceived benefits they derived....

    Personally I use an 78% nitrogen blend in all my tyres as I find it the best compromise of cost versus performance.
    FCN 5 belt driven fixie for city bits
    CAADX 105 beastie for bumpy bits
    Litespeed L3 for Strava bits

    Smoke me a kipper, I'll be back for breakfast.
  • optimisticbiker
    optimisticbiker Posts: 1,657
    madtam wrote:


    Anyone want to comment on using Helium or Hydrogen in tyres to reduce weight ?? :mrgreen:
    A 700C x 23mm tyre is about 0.59L (treating it as a torus with inner radius 0.304m and outer 0.327m) and therefore holds 4kg of air @ 6Bar (100psi) (using ideal gas law). Seems a bit high, but i can't see the flaw in my thinking...

    Helium is about 15% as dense as air so would weigh 0.6kg at the same pressure, but you couldnt use rubber tubes because they are porous to helium.
    Invacare Spectra Plus electric wheelchair, max speed 4mph :cry:
  • walkingbootweather
    walkingbootweather Posts: 2,443
    TGOTB wrote:
    The air in a single 21x700c tyre inflated to 100psi weighs around 4g. Can't be bothered to work it out for Helium, but it's clearly more than 0g. You'll gain more by having a haircut...
    .

    Isn't helium a 'lifting gas'? If you had big enough tyres couln't you make your bike effectively weightless?
    Nobody told me we had a communication problem
  • madtam
    madtam Posts: 141
    Do you always use the same nitrogen blend or do you change it depending on conditions ?



    On the Hydrogen/Helium front I have a feeling that to get the same pressure I think you end up with pretty much the same weight as unlike a latex balloon a bike tyre is pretty inflexible so you don't displace the air the same. Anyway the weight of the volume of any gas is so bloody small it is going to be pretty difficult to measure let alone notice.
  • Initialised
    Initialised Posts: 3,047
    nameinuse wrote:
    Makes me wonder why they don't fill those bulbs with nitrogen instead.
    Probably because liquid nitrogen would cool the tubes enough to make them crack.
    I used to just ride my bike to work but now I find myself going out looking for bigger and bigger hills.
  • team47b
    team47b Posts: 6,425
    Nitrus oxide so when you have a pun*ture you can simply laugh it off :oops:
    my isetta is a 300cc bike
  • SteppenHerring
    SteppenHerring Posts: 720
    OptimisticBiker wrote:
    madtam wrote:


    Anyone want to comment on using Helium or Hydrogen in tyres to reduce weight ?? :mrgreen:
    A 700C x 23mm tyre is about 0.59L (treating it as a torus with inner radius 0.304m and outer 0.327m) and therefore holds 4kg of air @ 6Bar (100psi) (using ideal gas law). Seems a bit high, but i can't see the flaw in my thinking...

    Helium is about 15% as dense as air so would weigh 0.6kg at the same pressure, but you couldnt use rubber tubes because they are porous to helium.
    I think I can see the flaw. 1 litre of nitrogen apparently has a mass of 1.251 grams. So a tyrefull at 6 bar could be 4 grams - not kilograms.

    CO2 is a bit heavier. Air is mostly N2 (molecular weight 28 ish) with a bit of O2 (32 ish) so CO2 at 44ish is a bit heavier.
  • steelie600
    steelie600 Posts: 519
    madtam wrote:
    Some car tyre places charge a premium to inflate with nitrogen because it doesn't permeate out as fast so the tyre stays up longer.

    Half true, yes for road cars this is the case but for race cars and bikes, the nitrogen is more stable than normal air and devoid of any water content. As when you heat up normal air it expands significantly more than just N2. Heat up N2 it hardly expands over the operating range of the tyre, which enables more precise tyre pressures and ultimately faster laps.

    Basically its cos theres no moisture in it!
    Idiot ^^^^^^^^^

    Ralph

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