# The ridiculous myth about letting bike tyres down when flying.



## Globalti (6 Jan 2012)

The post on BA and travelling with a bike prompts me to post this. 

Let's get this straight: the fuselage of a passenger aircraft is a sealed aluminium cylinder, pointed at the front and with a big round plate at the back, concave like the bottom of an aerosol can to resist internal pressure. The whole fuselage is pressurised to the equivalent of around 10,000 feet by compressors powered by the engines. This ensures there is sufficient oxygen available for healthy humans in the cabin and animals in the hold to breathe, as long as they remain sedentary.

Would your tyres explode if you rode your bike over a 10,000 ft Alpine pass? No, they would not.

So why listen to the carp about deflating your tyres before a flight? Because passengers and jobsworth arse-covering handling staff don't understand this simple principle, that's why.

The problems begin if the integrity of the fuselage is destroyed and pressure is lost. If this happens at 32,000 feet I expect there will be minor mayhem in passengers' luggage as tubes of toothpaste and bottles of shampoo will empty explosively while the odd packet of crisps might pop and passengers themselves will be a little distressed. However the pilot will descend rapidly to an altitude where there is enough oxygen and while he is descending, oxygen masks will drop to give a few minutes of safety margin.

I don't know how to calculate the pressures but I expect that at 32,000 feet a bicycle tyre in poor condition might bulge off the rim or pop as the threads fail at the weak spot but I'd be willing to bet that most would not.

Got it?


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## TheDoctor (6 Jan 2012)

It's simple. Standard atmospheric pressure is about 15 psi.
Would your tyres pop off the rim if you put an extra 15 psi in them? No.
Would, therefore, your tyres pop off the rim in a vacuum? Still no.
Is the air thin enough to be a near vacuum at 30-odd thousand feet? No.
Therefore no problem.


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## ColinJ (6 Jan 2012)

You are absolutely correct, but the trouble with jobsworths is that they don't like smartarses like us! 

On the subject of pressure changes in aircraft ...

I had terrible pressure problems with my ears and sinuses on my first few flights, but eventually discovered Earplanes which eliminated the problem for me. So, there I was on one flight to Spain with my Earplanes inserted, idly watching a young couple in the seats across the aisle playing tonsil tennis. I drank the last of the water from my 750 mL SIS bottle and closed the valve.

Eventually, the seat belt signs went on and we began our descent. I was blissfully unaware of the pressure changes involved until both young people started holding their ears and moaning. The young woman was in such pain that she started sobbing uncontrollably. I thought they were being a bit OTT until I glanced down at my water bottle and saw it being crushed almost flat by the ever-increasing air pressure! 

I've done some rapid descents off the big hills around Hebden Bridge and had my ears 'pop'. It never happens on the way up because I'm moving slowly and the pressures have time to equalise.


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## Brains (6 Jan 2012)

The issue is that FFA rules say planes should not be taking pressurised containers, aerosols, skuba tanks, tyres, camping gaz cylinders etc are all pressurised containers.
None are likely to blow at 30,000 ft and even if they did are unlikely to do any damage to the plane.

However having someting go 'bang' in the hold is most likly to cause your plane to be diverted to the nearest airport to see what happened.

I once spent an afternoon on the runway at Hamburg due to an alarm clock going off in the hold, they simply will not fly with any issues or potential issues outstanding, so I don't have a problem in deflating my tyres. Just take a pump for the other end.


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## Ticktockmy (6 Jan 2012)

[QUOTE 1670351, member: 45"]Who pumps up the plane tyres then when it's on its descent?[/quote]


Aircraft that will fly at higher altitudes, in the main use nitrogen.

Nitrogen won't entrain moisture, so the vast majority of jets require either nitrogen for the tires. While some compressors and storage tanks may exceed the industry standard, for compressors, of 125 psi, and may get to the ranges required for jets, dryers for regular air and the expense of maintenance makes it far less expensive to have nitrogen delivered virtually on demand by the AirGas, coming in cylinders with 4700psi crammed into them and allowing a mechanic to quickly, efficiently and easily service the tires of a jet up to the 225 or better psi that's required as determined by the manufacturer of the aircraft and the tire.

You also have the added safety of nitrogen being, as I mentioned before, an inert gas. Air contains, as well as nitrogen, oxygen, which is not an inert gas. Not only is it corrosive, in the form of a pure gas, it will spontaneously combust in the presence of petrochemicals, which are typically found in airplanes, in the wings, to which the landing gear is attached, and which most aircraft leak.
to sum up:
1. its non corrosive
2. its non flammable
3. it less likely to change its volume due to temp
4. it is less likely to change its volume at altitude.

Thus no one has to inflate the plane tyres when it decending.


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## Globalti (6 Jan 2012)

If bike tyres really were a danger to aircraft they would have been banned years ago along with hazardous materials. My company now employs three graduates who do nothing more than ensure our products are safety compliant for airfreight and seafreight.


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## TheDoctor (6 Jan 2012)

Ticktockmy said:


> Aircraft that will fly at higher altitudes, in the main use nitrogen.
> 
> Nitrogen won't entrain moisture, so the vast majority of jets require either nitrogen for the tires. While some compressors and storage tanks may exceed the industry standard, for compressors, of 125 psi, and may get to the ranges required for jets, dryers for regular air and the expense of maintenance makes it far less expensive to have nitrogen delivered virtually on demand by the AirGas, coming in cylinders with 4700psi crammed into them and allowing a mechanic to quickly, efficiently and easily service the tires of a jet up to the 225 or better psi that's required as determined by the manufacturer of the aircraft and the tire.
> 
> ...


 
Oxygen will spontaneously combust? Will it hell.
Petrochemicals will burn in air, if ignited, but an aircraft is sort of...surrounded by air anyhow.
Clue's in the name and all that.
Oxygen is a good oxidising agent, but air's pretty good at that too. If your wings are on fire, then the contents of the tyres are probably the least of your worries!!

DISCLAIMER - I am not an aircraft fitter or anything...


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## dragon72 (6 Jan 2012)

The check-in people always ask me, "Have you deflated your tyres?" 
I always lie, "Yes"
I never deflate them though. And nobody ever checks them physically.


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## TheDoctor (6 Jan 2012)

[QUOTE 1670880, member: 45"]No, but neither did you paste in some Google results.[/quote]
From here...


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## Brains (7 Jan 2012)

Globalti said:


> If bike tyres really were a danger to aircraft they would have been banned years ago along with hazardous materials. My company now employs three graduates who do nothing more than ensure our products are safety compliant for airfreight and seafreight.


 
It a pity a few more freighting companies don't do this.
We have just had to deal with a ship impounded in Finland, the reason was improper packing for the cargo which was bound for South Korea.
They had packed 120 Patriot missiles into cardboard boxes ! Loose, they had not even containerised them !


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## doog (7 Jan 2012)

I had what I consider to be a close call on a Ryan air flight in June. Just before my tour I had purchased some new Schwalbe marathon tyres. I had a blow out on the rear wheel in my garage when putting them on but really didnt think anything of it (although I thought they seemed a bit loose and easy to get on my rims) Inflated to 90psi went to the airport where some security guy asked if I had let them down (it was boxed and I lied)

At the other end I made the bike up at the front of the airport, cycled around the corner and the tube escaped from the rim and blew like a shotgun going off! 

With the suggested increase in pressure of 15psi when flying it must have been a close call. I was to have further blow outs on the tour( transpires the tyres are too big for the rims (25mm marathons on open pro's)


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## Peteaud (7 Jan 2012)

Ah but what about crisps.

On a plane the bag swells up, obviously if they are Walkers then the amount of air in the bag is even greater, but wouldnt a bike tyre do the same.


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## ColinJ (7 Jan 2012)

Brains said:


> It a pity a few more freighting companies don't do this.
> We have just had to deal with a ship impounded in Finland, the reason was improper packing for the cargo which was bound for South Korea.
> They had packed 120 Patriot missiles into cardboard boxes ! Loose, they had not even containerised them !


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## TheDoctor (7 Jan 2012)

Peteaud said:


> Ah but what about crisps.
> 
> On a plane the bag swells up, obviously if they are Walkers then the amount of air in the bag is even greater, but wouldnt a bike tyre do the same.


 
Indeed it would.
Crisp bags aren't built to handle 100 psi, though, and bike tyres are.
That's the difference.


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## slowmotion (7 Jan 2012)

1672063 said:


> I do that with my regular luggage. I get a random stranger off the street to pack my bag and lie about it when asked.


Top tip. I'll use that one when I next saunter through the Green Channel with a whole load of white powder.


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## fenlandpsychocyclist (8 Jan 2012)

If you look at the galaxy c5 aircraft, that has 28 tyres to take its weight of 350 tonnes ... thats a seriously big aircraft.

Now compare to the space shuttle that has 6 tyres to take its weight of 100 tonnes ... meaning those tyres have to be filled to
a very high pressure. And they spend up to 16 days in the vacuum of space without going ... pop!!


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## Globalti (8 Jan 2012)

Bike tyres are already pumped up hard and are immensely strong so another few percent of relative pressure isn't going to bother them.

A crisp packet is nowhere near inflated at sea level; at 10,000 ft they can be quite well inflated and being completely inflexible and designed for easy opening I expect they would burst at a seam at much higher than that.


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## frank9755 (8 Jan 2012)

Have fun taking the piss out of people who man airport baggage handling operations by telling them that there is a risk that a bike tyre could explode while on a plane and that it needs to be deflated. Occasionally one will believe this and prove his or her stupidity by proclaiming this gospel to members of the public.

Ironically, what does make tyres explode is the high temperatures encountered inside a parked car on a hot day. It's not that uncommon to have tyres go 'pop' - it happened to me last summer when I couldn't be bothered to take my racing bike out of the car when I got home. Happily the car wasn't a write-off 

Given that aircraft holds are generally a bit chilly, I suspect that tyres are less likely to explode in a plane than they are in everyday use.


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## Globalti (8 Jan 2012)

Interesting point. In an aircraft hold your tyres might be at 10 degrees C or lower; in a car in sunshine they could reach 50 or more.


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## Globalti (8 Jan 2012)

Does this mean I should keep my rubber in the 'fridge?


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## byegad (8 Jan 2012)

Ticktockmy said:


> Aircraft that will fly at higher altitudes, in the main use nitrogen.
> 
> Nitrogen won't entrain moisture, so the vast majority of jets require either nitrogen for the tires. While some compressors and storage tanks may exceed the industry standard, for compressors, of 125 psi, and may get to the ranges required for jets, dryers for regular air and the expense of maintenance makes it far less expensive to have nitrogen delivered virtually on demand by the AirGas, coming in cylinders with 4700psi crammed into them and allowing a mechanic to quickly, efficiently and easily service the tires of a jet up to the 225 or better psi that's required as determined by the manufacturer of the aircraft and the tire.
> 
> ...


 
And Nitrogen makes up around 80% of air.

Frankly the rules is stupid, even an unpressurised hold would not add 1 bar of pressure and would be a lot colder than the cabin so reducing pressure rather than increasing it. P.V/T remains constant so is you drop the temperature from 20C to -30C this is a drop of approximately 20% whereas a high pressure tyre at 100psi would only go up by 15% in a vacuum. 

So a requirement to reduce trye pressure by 15% or 20% of full sidewall rating would be an ultra cautious and less inconvenient precaution. I'd like to see Ryan air test a few bike tyres in their hold rather than their testing of flying conditions near volcanoes.


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## frank9755 (8 Jan 2012)

byegad said:


> And Nitrogen makes up around 80% of air.
> I'd like to see Ryan air test a few bike tyres in their hold rather than their testing of flying conditions near volcanoes.


 
To be fair to Ryanair, last time I looked, their rules explicitly stated that tyres do not need to be deflated.

The deflation thing is an urban myth amongst the baggage handler community and, it has to be said, some cyclists.


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## Globalti (8 Jan 2012)

frank9755 said:


> To be fair to Ryanair, last time I looked, their rules explicitly stated that tyres do not need to be deflated.
> 
> The deflation thing is an urban myth amongst the baggage handler *jobsworth* community and, it has to be said, some cyclists.


 
Fixed that for you.


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## Bromptonaut (8 Jan 2012)

fenlandpsychocyclist said:


> If you look at the galaxy c5 aircraft, that has 28 tyres to take its weight of 350 tonnes ... thats a seriously big aircraft.
> 
> Now compare to the space shuttle that has 6 tyres to take its weight of 100 tonnes ... meaning those tyres have to be filled to
> a very high pressure. And they spend up to 16 days in the vacuum of space without going ... pop!!


 
Both are designed to fly though, bike tyres are not. I suspect it's one of those marginal things where some airlines risk managers regard as requiring a control and others dont. If asked why not just do it? 

On the Galaxy the tyres can be inflated/deflated in flight. High pressure for departure from base, lower for landing on rough/ready forward airstips - where all the wheels are needed to spread the weight.

A laden Galaxy can land and stop in 1200m. Even medium size commercial airliners need around 2000. Any less and it's special briefing and Captain's landing


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## fenlandpsychocyclist (8 Jan 2012)

Bromptonaut said:


> On the Galaxy the tyres can be inflated/deflated in flight. High pressure for departure from base, lower for landing on rough/ready forward airstips - where all the wheels are needed to spread the weight.
> 
> A laden Galaxy can land and stop in 1200m. Even medium size commercial airliners need around 2000. Any less and it's special briefing and Captain's landing


 
Whoo .. clever, i didn't know that about their in-flight tyre management!!
I've seen the c5's land/takeoff at mildenhall (only 32 miles by bike from home).
Love the noise of those engines, especially when they come over wisbech at 8000 feet and and make "adjustments" to the engine revs
as one did a few weeks ago.

This video from 1min 45secs is the sort of noise i'm on about: 
View: http://www.youtube.com/watch?v=LvNwiczJ69k


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## Little yellow Brompton (8 Jan 2012)

fenlandpsychocyclist said:


> If you look at the galaxy c5 aircraft, that has 28 tyres to take its weight of 350 tonnes ... thats a seriously big aircraft.
> 
> Now compare to the space shuttle that has 6 tyres to take its weight of 100 tonnes ... meaning those tyres have to be filled to
> a very high pressure. And they spend up to 16 days in the vacuum of space without going ... pop!!


The C5 can change it's tyre pressures mid flight, so the problem of going pop ( or not ) doesn't arrise


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## Little yellow Brompton (8 Jan 2012)

Bromptonaut said:


> Both are designed to fly though, bike tyres are not. I suspect it's one of those marginal things where some airlines risk managers regard as requiring a control and others dont. If asked why not just do it?


 My money is more on outdated risk controls from the days of Rapides or DC3s, it's comparable to the decades out of date ban on mobile phones in hospitals.


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## Little yellow Brompton (8 Jan 2012)

Bromptonaut said:


> Both are designed to fly though, bike tyres are not. I suspect it's one of those marginal things where some airlines risk managers regard as requiring a control and others dont. If asked why not just do it?
> 
> On the Galaxy the tyres can be inflated/deflated in flight. High pressure for departure from base, lower for landing on rough/ready forward airstips - where all the wheels are needed to spread the weight.


 Although they were designed with that in mind it's very very, rare that a C5 would end up on a forward strip . The cost too much to risk compared with the alterative of transhipping to cheaper AC


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## dragon72 (8 Jan 2012)

I want to know why I can't listen to my iPod Nano on a plane...


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## frank9755 (8 Jan 2012)

Bromptonaut said:


> A laden Galaxy can land and stop in 1200m.


 
My Super Galaxy can stop far quicker than that, even with a full touring load, going downhill!


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## fenlandpsychocyclist (8 Jan 2012)

frank9755 said:


> My Super Galaxy can stop far quicker than that, even with a full touring load, going downhill!


 
What ... with the full 96 tonne payload onboard?
Thats my kind of training bike.


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## Alun (8 Jan 2012)

dragon72 said:


> I want to know why I can't listen to my iPod Nano on a plane...


Because it will distract you from buying all the overpriced crap on the plane


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## BigAndyH (12 Jan 2012)

> You also have the added safety of nitrogen being, as I mentioned before, an inert gas. Air contains, as well as nitrogen, oxygen, which is not an inert gas. Not only is it corrosive, in the form of a pure gas, it will spontaneously combust in the presence of petrochemicals, which are typically found in airplanes, in the wings, to which the landing gear is attached, and which most aircraft leak.
> to sum up:
> 1. its non corrosive
> 2. its non flammable
> ...


 
For an ideal gas PV/T = constant, and since N2 is near enough an ideal gas for our purposes, and is the major component of air, its volume will change with temp and pressure in almost exactly the same way as for air.



byegad said:


> Frankly the rules is stupid, even an unpressurised hold would not add 1 bar of pressure and would be a lot colder than the cabin so reducing pressure rather than increasing it. P.V/T remains constant so is you drop the temperature from 20C to -30C this is a drop of approximately 20% whereas a high pressure tyre at 100psi would only go up by 15% in a vacuum.


 
But temperature needs to be in Kelvin, so from 293 to 303 - a drop of only 3.4%, though in reality I'm sure the hold will get a lot colder than 20 C. The lower temp will reduce the gas volume, thus countering the effect of reduced pressure ( which will cause the gas to expand).


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## Ticktockmy (12 Jan 2012)

Normally the holds are heated, unless they are carying a stiffy, then the heating get turned off, and then not always, nothing worse than getting into the hold to find they have been cooking a stiffy for 13 hours. LOL Dont ahhf make them fart


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## steveindenmark (27 Jan 2012)

I work on the premis that it is not my plane and if you come in my house you follow my rules.

It makes everyone so much happier.

Steve


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## yello (27 Jan 2012)

> I work on the premis


 
I've worked on a number of premises in my time.


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## rollinstok (27 Jan 2012)

There is a fundamental flaw in your argument.. bicycle tyres are not designed to handle 500mph. I have done an equation and calculated that 4.37% of the air pressure in any bicycle tyre should be exhausted via the valve prior to boarding the aircraft, regardless of recommended maximum pressure of said tyre. I work for the EEC therefore I am correct.


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## Little yellow Brompton (27 Jan 2012)

steveindenmark said:


> I work on the premis that it is not my plane and if you come in my house you follow my rules.
> 
> It makes everyone so much happier.
> 
> Steve


I work on the premise that if I have paid to rent space then we agree the rules when I pay.


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## steveindenmark (27 Jan 2012)

You mean like the rule:

You let your tyres down? 

Steve


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## Little yellow Brompton (27 Jan 2012)

steveindenmark said:


> You mean like the rule:
> 
> You let your tyres down?
> 
> Steve


There is no rule, therefore when I pay no rule was agreed.


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