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Tyre pressure loss - what's going on?

navrig2navrig2 Posts: 1,511
edited October 2019 in Road general
I recently moved to the middle east and getting out for a ride hasn't been that easy because of the extreme heat.

I managed it 2 weekends ago. I had to rely on a CO2 cannister to get my tyres up to pressure as I hadn't bought a track pump at that point and I couldn't get enough pressure with the pocket pump. The CO2 got the tyres hard enough.

It was a short, hot and humid ride and the roads have a lot of debris - sand and small stones. The next morning both tyres were soft.

I decided it was time to get a track pump.

The tyres had been on the bike for a while and were thinning so I replaced them and the tubes. Pumped them up with the track pump and they have been sitting for a few days and no sign of pressure loss. All good.

I then looked at the old tyres and they were thin and have a few small stone cuts on the running surface. So I ditched them. I checked the old tubes by putting in some air and listening and feeling for leaks. Nothing. I added a bit more air, tightened the valves and left them. 4 days later they are still inflated and showing no signs of leaking.

So why did the old tyres with the old tubes deflate the day after the ride? Really strange.

Posts

  • sungodsungod Posts: 12,204
    co2 will escape from butyl far more rapidly than air
    my bike - faster than god's and twice as shiny
  • The rubber used in inner tubes is permeable to CO2 so this allow the tyres to deflate more quickly. I only use CO2 if i puncture whilst out then, when I get back home, deflate the tube and refill with air.
  • navrig2navrig2 Posts: 1,511
    I was aware of the incompatibility of CO2 and some inner tube materials but it was the speed of deflation which bothered me. 24-36 hours and the tyre was soft enough to press the tyre onto the inner wheel surface. When I have used CO2 previously it has taken the best part of the week to achieve that level of deflation.

    A quick Google suggests it's not particle size (permeability) but a chemical relationship between CO2 and butyl rubber:

    http://www.exploringoverland.com/overla ... fuhk7ouscc

    It still doesn't explain the deflation unless the increased ambient temperature has an effect. The outside temperature during the ride would have been 34+ degrees and during the day in the apartment probably almost 30 degrees. The aircon would drop that to 23 during the evening rising towards 30 again by morning.

    Given that generally heat increases endothermic reactions I suspect the softer butyl material was more reactive to the CO2.

    Then again I am a civil engineer, what do I know?
  • Wiggle?
    Advocate of disc brakes.
  • daniel_bdaniel_b Posts: 8,484
    Wiggle?

    Probably Merlin.
    Felt F70 05 (Turbo)
    Marin Palisades Trail 91 and 06
    Scott CR1 SL 12
    Cannondale Synapse Adventure 15 & 16 Di2
    Scott Foil 18
  • navrig2navrig2 Posts: 1,511
    Daniel B wrote:
    Wiggle?

    Probably Merlin.

    Nope. Merlin doesn't deliver here but Wiggle does, so Wiggle.
  • Maybe an engineer but you first reply doesn’t come across as very civil.

    Nothing in your first post to point to you being aware of CO2 and butyl tubes hence the replies you got.
  • daniel_bdaniel_b Posts: 8,484
    navrig2 wrote:
    Daniel B wrote:
    Wiggle?

    Probably Merlin.

    Nope. Merlin doesn't deliver here but Wiggle does, so Wiggle.

    I blame Merlin for not delivering to the middle east in that case.
    Culpable at least.
    Felt F70 05 (Turbo)
    Marin Palisades Trail 91 and 06
    Scott CR1 SL 12
    Cannondale Synapse Adventure 15 & 16 Di2
    Scott Foil 18
  • navrig2navrig2 Posts: 1,511
    Maybe an engineer but you first reply doesn’t come across as very civil.

    Nothing in your first post to point to you being aware of CO2 and butyl tubes hence the replies you got.

    Not sure what is not civil about my reply and I profusely apologise for not declaring my full knowledge and understanding.

    The replies to my first post were very useful as they prompted my memory of the CO2 issue however the speed of deflation made me explore it further and resulted in more knowledge about the issue. I decided to share that increased knowledge but my apologies for trying to be sharing. :shock:

    Grief!!
  • navrig2navrig2 Posts: 1,511
    Daniel B wrote:
    navrig2 wrote:
    Daniel B wrote:
    Wiggle?

    Probably Merlin.

    Nope. Merlin doesn't deliver here but Wiggle does, so Wiggle.

    I blame Merlin for not delivering to the middle east in that case.
    Culpable at least.

    Fair point. I'll raise this with Merlin next time I order something from them :D

    I wonder if I order from Wiggle and have it delivered will the Haribro be liquid when it arrives?
  • imposter2.0imposter2.0 Posts: 10,839
    navrig2 wrote:
    Then again I am a civil engineer, what do I know?

    You’ll know how to pour concrete...?
  • navrig2navrig2 Posts: 1,511
    Imposter wrote:
    navrig2 wrote:
    Then again I am a civil engineer, what do I know?

    You’ll know how to pour concrete...?


    Yup :D, amongst a few other things.
  • First.AspectFirst.Aspect Posts: 3,417
    navrig2 wrote:
    Imposter wrote:
    navrig2 wrote:
    Then again I am a civil engineer, what do I know?
    You’ll know how to pour concrete...?
    Yup :D, amongst a few other things.

    Please can you make more effort to make motorway bridges and multi-storey car parks more attractive in future.
  • navrig2navrig2 Posts: 1,511
    navrig2 wrote:
    Imposter wrote:
    navrig2 wrote:
    Then again I am a civil engineer, what do I know?
    You’ll know how to pour concrete...?
    Yup :D, amongst a few other things.

    Please can you make more effort to make motorway bridges and multi-storey car parks more attractive in future.

    You are asking an engineer to consider form rather than function!! You don't know engineers very well do you :lol: ?
  • First.AspectFirst.Aspect Posts: 3,417
    navrig2 wrote:
    navrig2 wrote:
    Imposter wrote:
    navrig2 wrote:
    Then again I am a civil engineer, what do I know?
    You’ll know how to pour concrete...?
    Yup :D, amongst a few other things.

    Please can you make more effort to make motorway bridges and multi-storey car parks more attractive in future.

    You are asking an engineer to consider form rather than function!! You don't know engineers very well do you :lol: ?
    Good point. It's a bit like asking IT to test something before declaring it fixed.

    Sorry.
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