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Tyre pressure on a plane...

NFMCNFMC Posts: 232
edited February 2008 in Tour & expedition
...I've read that you have to deflate your tyres when taking them on a plane.

Is there a definite reason to do this as I like my tyres as hard as possible and I'm only taking a hand-pump with me.

I'm guessing it has something to do with the pressure on the plane??? Is it extreme enough to knacker the tyre/valve?

Posts

  • andymillerandymiller Posts: 2,856
    I think it's an urban myth.
  • terongiterongi Posts: 318
    I think it used to br true when the cargo holds of aeroplanes were not pressurised like the cabin.

    My leaky memory of physics is that air pressure at altitude is lower, so the inner tubes would expand and could burst.

    Nowadays I think the cargo hold is pressurised like the cabin, so this is no longer an issue.

    You should check though, because I know they won't let you take co2 canisters on a plane (hold luggage or hand luggage). I'm not sure why that is, though.

    I'm sure the airline will tell you if you ask them; after all they're not particularly going to want things going bang in the hold of a passenger jet these days.

    Someone who knows what they are talking about might be along soon.
  • BrainsBrains Posts: 1,732
    andymiller wrote:
    I think it's an urban myth.

    Not at all, we have had to deflate our tyres on several occasions.

    It's not a totally unreasonable request as planes are not permitted to carry pressurised items, there is also an outside chance that when the air in your type expands as the plane climbs higher (remember the hold is not pressurised to the same degree as the the passenger section) so it could in theory explode.

    The solution is to not totally deflate the tyres, just make them appear flat, and then do your best with the hand pump at the airport on arrival and then stop at the 1st bike shop and borrow their track pump
  • grimpeurgrimpeur Posts: 230
    Let's do some maths.

    Average pressure at sea level = ~1 atm = ~14.7psi

    Average crusing altitude of airline = ~37000ft

    Average pressure at 37000ft = ~0.197atm = ~2.903psi

    delta = 14.7 - 2.903 = ~11.8 psi

    so a tyre pumped to 100psi at sea level would effectively be at 111.8psi at altitude.

    Any tyre is more than capable of handling that provided it is not over inflated. As always though, it is worth adding in a little safety room, so if you normally run 120 psi in your road tire deflate slightly to, say, 90 psi and you will be fine.
  • BrainsBrains Posts: 1,732
    The reason why baggage handlers are baggage handlers is partially due to their inability to do maths.

    Hence unless the tyre is visibly nearly flat you will not get past.
  • dennisndennisn Posts: 10,496
    grimpeur wrote:
    Let's do some maths.

    Average pressure at sea level = ~1 atm = ~14.7psi

    Average crusing altitude of airline = ~37000ft

    Average pressure at 37000ft = ~0.197atm = ~2.903psi

    delta = 14.7 - 2.903 = ~11.8 psi

    so a tyre pumped to 100psi at sea level would effectively be at 111.8psi at altitude.

    Any tyre is more than capable of handling that provided it is not over inflated. As always though, it is worth adding in a little safety room, so if you normally run 120 psi in your road tire deflate slightly to, say, 90 psi and you will be fine.

    Got to agree here. You could pump up your tires at the seashore, then send them to
    the moon and they probably would be ok.

    Dennis Noward
  • terongiterongi Posts: 318
    dennisn wrote:

    Got to agree here. You could pump up your tires at the seashore, then send them to
    the moon and they probably would be ok.

    Dennis Noward

    That is plainly ridiculous.

    You would need off-road tyres on the moon and they would not need to be inflated to such high pressures in the first place.
  • I got half way through an explaination of tyre pressures to a woman at the check in desk once, before realising and saying "this isn't going to change your mind, is it?" and giving up and letting the tyres all the way down :(
  • NFMCNFMC Posts: 232
    Thanks all...

    ...I'm taking the bike in a bike bag with internal bags for the tyres so I'm going to ram them up and worry about it when I get there.
  • I pump them up at the destination airport, then ride to a local service station and use their high-pressure hose to get them topped up. If you have Presta valves, you'll need to get a small adaptor fitting from your LBS.

    Obviously be careful with the high-pressure hose - it only takes a second or two to get tubes fully inflated.
    It's an uphill climb to the bottom
  • If you read the instructions on ryanair they tell you it is not necessary! They advise that you may wish to incase the tube bursts but considerately they mention you have to consider the inconvienance of re inflating. Therefore it is an urban myth perpetuated by some airlines.
    Peter
  • andrew_sandrew_s Posts: 2,511
    grimpeur wrote:
    Let's do some maths.
    Average pressure at sea level = ~1 atm = ~14.7psi
    Average crusing altitude of airline = ~37000ft
    Average pressure at 37000ft = ~0.197atm = ~2.903psi

    delta = 14.7 - 2.903 = ~11.8 psi

    so a tyre pumped to 100psi at sea level would effectively be at 111.8psi at altitude.

    Any tyre is more than capable of handling that provided it is not over inflated. As always though, it is worth adding in a little safety room, so if you normally run 120 psi in your road tire deflate slightly to, say, 90 psi and you will be fine.

    But aircraft baggage holds are pressurised to the same level as the cabin. Pets go in the hold, although the reason for pressurisation is so that the cabin floor doesn't have to be so strong (and therefore heavier).
    That pressure is equivalent to about 2000 to 2400m, as reported by the altimeter on my cycle computer. You are thus looking at a change of effective pressure of about 4psi
  • grimpeurgrimpeur Posts: 230
    Indeed I was assuming a worst case scenario in which the hold wasn't pressurized. But as you point out, on modern aircraft it is thus negating the need to do anything to your tyre on boarding a flight.
  • Before you go to the airport pump the tyres up to maximum. If they tell you to let the air out, press the valve in so air gushes out and then slowly let the valve back up so the gushing air gradually comes to a stop. The baggage handler will think they are empty and you will still have plenty of air in the tyre!

    More air in the tyre the better, they are never going to pop and there is a high chance the airline will drop your bike.
  • BrainsBrains Posts: 1,732
    . Therefore it is an urban myth perpetuated by some airlines.
    Peter

    Actually it's the Baggage Handling companies. Very few of the airlines do their own baggage handling, most airports have a single baggage handling company.

    However as the myth is perpetuated by the baggage handling companies, from several personal experiences you are unlikely to get past check in without making your tyres visibly flat.
  • pneumaticpneumatic Posts: 1,989
    The first time I took bike on plane, and not having done the maths (thanks for that, oh numerate ones), I sat on the plane in a cold sweat when I realised that I had forgotten to let the air out. I was sure the tyres would explode. Of course they didn't, so now I don't bother.

    Anyway, if you use a bike bag, they don't look.


    Fast and Bulbous
    Peregrinations
    Eddingtons: 80 (Metric); 60 (Imperial)

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