# When flying, deflate tires?



## mustang1 (8 May 2016)

I packed my bike up for its first flight and deflated the tires almost completely. I've read people deflate complete to others who don't deflate at all. How about you?


----------



## Yellow Saddle (8 May 2016)

I would love to know why airlines make you deflate the tyres. Can anyone shed light on this rule?


----------



## byegad (8 May 2016)

The theory from the airline's point of view is that in an unpressurised hold the drop in external air pressure will cause the tyre to blow. Given air pressure at sea level is 14psi or there abouts, if your tyre is inflated to the maximum allowed (sidewall) pressure less 14psi it will have no effect. In theory in a vacuum the internal pressure will have the same effect as full pressure at sea level. In reality the drop in temperature at altitude will mitigate the loss in external pressure anyway.


----------



## screenman (8 May 2016)

Yellow Saddle said:


> I would love to know why airlines make you deflate the tyres. Can anyone shed light on this rule?



They read about it on the net.


----------



## screenman (8 May 2016)

I think the idea might date back to when planes had outside toilets.


----------



## Deleted member 23692 (8 May 2016)

I wonder if they deflate the undercarriage tyres too


----------



## gavintc (8 May 2016)

screenman said:


> I think the idea might date back to when planes had outside toilets.


The ones on the wings were the most challenging. Thank goodness, they developed to the system described by Billy Connolly; 
View: https://www.youtube.com/watch?v=CcOn5_SbCSA


----------



## midliferider (8 May 2016)

I did this first time I took the bike on the plane. Now I don't do it at all. They won't ask you any questions as long as you have paid the exorbitant fee that they charge.


----------



## Lonestar (8 May 2016)

Yellow Saddle said:


> I would love to know why airlines make you deflate the tyres. Can anyone shed light on this rule?



Air we go?


----------



## screenman (8 May 2016)

midliferider said:


> I did this first time I took the bike on the plane. Now I don't do it at all. They won't ask you any questions as long as you have paid the exorbitant fee that they charge.



Is it expensive to take a bike with you? I always thought it was good value.


----------



## Yellow Saddle (8 May 2016)

byegad said:


> The theory from the airline's point of view is that in an unpressurised hold the drop in external air pressure will cause the tyre to blow. Given air pressure at sea level is 14psi or there abouts, if your tyre is inflated to the maximum allowed (sidewall) pressure less 14psi it will have no effect. In theory in a vacuum the internal pressure will have the same effect as full pressure at sea level. In reality the drop in temperature at altitude will mitigate the loss in external pressure anyway.


All the planes I've flow in other than my brother's Piper Cub, the hold is pressurized. My dogs can testify to that, as can the livestock frequently carried on airplanes. I've been on an Air Mauritius flight where the smell of goat was so strong nobody chose the meat options on the in-fight meal. I made up the bit about instant vegetarians, but you get the point. Even the air in the hold and cabin is all the same recycled air.


----------



## Keith Oates (8 May 2016)

The times I've flown with a bike the ground staff have always told me to deflate the tyres. If it is necessary or not never mind it's the airlines rules so conform to them. The same thing applies to switching off your mobile, if you are asked to do it then follow the request as it's not going to cost you anything.!!!!!!!!!!!!


----------



## Yellow Saddle (8 May 2016)

Keith Oates said:


> The times I've flown with a bike the ground staff have always told me to deflate the tyres. If it is necessary or not never mind it's the airlines rules so conform to them. The same thing applies to switching off your mobile, if you are asked to do it then follow the request as it's not going to cost you anything.!!!!!!!!!!!!


Yeah yeah, civil obedience and all that. I'd like to know why. Why can't I ask that question? I'm a naturally curious person.


----------



## Mad Doug Biker (8 May 2016)

Ffoeg said:


> I wonder if they deflate the undercarriage tyres too



That is exactly what I thought when I read this too!
I mean, the tyres have to be hard enough for the gear to take the strain when taking off/landing, so how would that work? Are they filled with something special stuff that doesn't expand? ....... Self deflating and inflating tyres? (A load of bull, I know)...... What?


----------



## ufkacbln (8 May 2016)

They used nitrogen gas in undercarriage tyres as the pressure effect is less than air.

The downside is that they do lose pressure quickly (something like 5% per day IIRC)

At least one air crash has been cause by these defective pressures or air being used instead of Nitrogen


----------



## Deleted member 23692 (8 May 2016)

They use nitrogen in aircraft tyres to eliminate moisture, which freezes due to the low temp at high alititude. The ice can throw the tyre/wheel out of balance causing unwanted vibrations on landing. It also helps control temperature, and changes in pressure due to moisture presence too.

Nitrogen also has bigger molecules than oxygen, so tyres containing pure N will deflate slower than those containing air.

All the above just leads to consistency in usage


----------



## bigjim (8 May 2016)

My B I law is a BA captain and says it's nonsense. Not needed in modern planes. I've had at least two bike bags damaged as the handlers have torn them open in order to deflate my tyres. If I box my bike I never deflate the tyres. I've not been asked about them for years by check in.


----------



## fatblokish (8 May 2016)

Last time I flew I didn't deflate 'em, but someone in the ground drew decided to do this for me. Next time I fly I will deflate them to the point where they feel squishy, in the hope that the ground crew will not deflate them any further to save me the effort of fully pumping them up when I arrive.


----------



## midliferider (8 May 2016)

screenman said:


> Is it expensive to take a bike with you? I always thought it was good value.



Yes it is always good to take your own bike perhaps except a place like Majorca where renting is relatively cheaper and you get good choice.

But airline charge is excessive when compared to what they charge for other similar items. This is specially true for Ryan air.


----------



## screenman (8 May 2016)

I suppose we have to balance things out a bit, Ryan Air cheap tickets higher other costs, other carrier higher ticket etc.


----------



## jefmcg (8 May 2016)

I heard it's because lower pressure tyres on trucks and tractors can and do explode leading to potentially dangerous bits if tyre flying around the hold. So they make a blanket rule for tyres, rather than a complicated one.


----------



## bigjim (8 May 2016)

jefmcg said:


> I heard it's because lower pressure tyres on trucks and tractors can and do explode leading to potentially dangerous bits if tyre flying around the hold. So they make a blanket rule for tyres, rather than a complicated one.


I think that may relate to unpressurised cargo plane holds. passenger jets have pressurised holds so the pressure is more or less the same as at ground level.


----------



## jefmcg (8 May 2016)

bigjim said:


> I think that may relate to unpressurised cargo plane holds. passenger jets have pressurised holds so the pressure is more or less the same as at ground level.


I'm still holding out for "simple rule". Deflate all tyres on all flights. Done. No confusion, no ambiguity. Only a slight chore at the far end.


----------



## Ajax Bay (8 May 2016)

If they ask, say that you have and write that on the box.


Ffoeg said:


> Nitrogen also has bigger molecules than oxygen,


Unless this is a canard; err, no: N2, O2. Li Be B C N O F Ne.

Edit after @Ffoeg post: See his link.


----------



## Deleted member 23692 (8 May 2016)

Ajax Bay said:


> err, no


Err yes

http://www.getnitrogen.org/pdf/graham.pdf


----------



## Yellow Saddle (8 May 2016)

jefmcg said:


> I'm still holding out for "simple rule". Deflate all tyres on all flights. Done. No confusion, no ambiguity. Only a slight chore at the far end.


Slight chore?

Have you ever seen what a mess a deflated MTB tyre with tubeless sealant makes if it is deflated? The bead pops off, out comes 2l of goop and you have a huge mess. It is impossible to re-inflate at the other end without lots of hands, plenty of cable ties, 16 tyre levers and a 300hp compressor.


----------



## Supersuperleeds (8 May 2016)

screenman said:


> I think the idea might date back to when planes had outside toilets.



any excuse to post this:


----------



## DaveReading (8 May 2016)

bigjim said:


> I think that may relate to unpressurised cargo plane holds. passenger jets have pressurised holds so the pressure is more or less the same as at ground level.



Yes, the only unpressurised passenger aircraft you are likely to find yourself flying on (to the Outer Hebrides, for instance) are little 19-seaters that you'd never get a bike on anyway.


----------



## Profpointy (8 May 2016)

Cunobelin said:


> They used nitrogen gas in undercarriage tyres as the pressure effect is less than air.
> 
> The downside is that they do lose pressure quickly (something like 5% per day IIRC)
> 
> At least one air crash has been cause by these defective pressures or air being used instead of Nitrogen



i would be astonished if a single crash has been caused by inflating with air instead of nitrogen. Defective tyres I could believe - but the difference btween 78% nitrogen and 100% nitrogen - don't believe it


----------



## Brandane (8 May 2016)

screenman said:


> Is it expensive to take a bike with you? I always thought it was good value.



It is good value if you avoid the likes of EasyAir/RyanJet.. BA will carry it as part of your luggage allowance; so as long as it (and any other check in luggage) is within your 1 piece/23kg limit then it won't cost you anything.

I voted for no deflation. I have taken my bike to Florida twice. This year it involved 3 flights and two airlines (BA/AA) outbound and 2 flights (both BA) inbound. I took my Tricross which has 28mm tyres at 90 psi, so not exceptionally high pressure. The bike and aircraft both survived, as they have done on several other flights.


----------



## ufkacbln (8 May 2016)

Profpointy said:


> i would be astonished if a single crash has been caused by inflating with air instead of nitrogen. Defective tyres I could believe - but the difference btween 78% nitrogen and 100% nitrogen - don't believe it



Google Mexicana Flight 940

One of the key findings as the cause was one of the wheels in the central undecarriage containing pressurised air as opposed to Nitrogen

If you still don't believe, take it up with the official investigators


----------



## screenman (8 May 2016)

Are the comparable in initial ticket price? I only ask as next year I intend to cycle a bit in other countries.


----------



## Profpointy (8 May 2016)

Cunobelin said:


> Google Mexicana Flight 940
> 
> One of the key findings as the cause was one of the wheels in the central undecarriage containing pressurised air as opposed to Nitrogen
> 
> If you still don't believe, take it up with the official investigators



I'm afraid I still don't believe. If they are really saying the margin os that tight that a little bit of oxygen os that disasterous they had already been sailing extremely close to the wind. Now if the nitrogen thing was one of a long list of failings along with not screwing the wings on properly or whatever, then fair enough


----------



## Fab Foodie (8 May 2016)

mustang1 said:


> I packed my bike up for its first flight and deflated the tires almost completely. I've read people deflate complete to others who don't deflate at all. How about you?


Never do when I put the Brommie in the hold.


----------



## ianrauk (8 May 2016)

No point. Keep inflated. No one checks.


----------



## Brandane (8 May 2016)

screenman said:


> Are the comparable in initial ticket price? I only ask as next year I intend to cycle a bit in other countries.


As always, it depends...... Obviously if I fly anywhere it's from Scotland which sometimes involves an extra flight to London/Amsterdam/Paris or wherever for a connection. That can severely bump up the price on the "budget" airlines. Strangely that isn't always the case on BA, in fact I posted about this at the time when I booked my flights to Orlando back in December. Flying Glasgow to London, then London to Orlando, the quoted cost was less than flying from London to Orlando! (I double checked it).
For European flights e.g. to Bordeaux 2 years ago - again by the time I had factored in the total cost of fare + luggage + whatever other extra charges various airlines throw in; I was cheaper flying with BA..


----------



## classic33 (8 May 2016)

Profpointy said:


> I'm afraid I still don't believe. If they are really saying the margin os that tight that a little bit of oxygen os that disasterous they had already been sailing extremely close to the wind. Now if the nitrogen thing was one of a long list of failings along with not screwing the wings on properly or whatever, then fair enough


http://aviation-safety.net/database/record.php?id=19860331-1&lang=en
Read the bottom of the page.
or
http://ecperez.blogspot.co.uk/2009/09/crash-of-mexicana-de-aviacion-flight.html


----------



## ufkacbln (8 May 2016)

Profpointy said:


> I'm afraid I still don't believe. If they are really saying the margin os that tight that a little bit of oxygen os that disasterous they had already been sailing extremely close to the wind. Now if the nitrogen thing was one of a long list of failings along with not screwing the wings on properly or whatever, then fair enough




As I said, you can believe or not.... many sources reporting the official investigation of the crash

From the Aviation Safety Network, 



> Flight 940 took off from Mexico City (MEX) at 08:40 for a flight to Puerto Vallarta (PVR), Mazatlán (MZT) and Los Angeles (LAX). The left main gear brake was overheated during the takeoff run. When the aircraft had reached FL310 the heat caused a tyre on the left hand main gear to explode. Fuel and hydraulic lines were ruptured and electrical cables severed resulting in a cabin decompression. An emergency was declared, but spilt fuel ignited and caused a massive fire on board. Control was lost and the aircraft crashed into a mountain in the Sierra Madre, at an elevation of 9000 feet._* It was found that the tire had been serviced with air rather than nitrogen. The air, under high temperature and pressure, resulted in a chemical reaction with the tire itself. This led to a chemical explosion of the tire.*_




Flight Safety Australia:



> Nitrogen inflation serves a vital safety purpose in aircraft tyres, as demonstrated by the horrible fate of Mexicana Airlines flight 940. It was a Boeing 727 that crashed in 1986 after a dragging brake overheated a wheel on take-off, eventually causing an explosion and fire after the gear was retracted. All 167 on board died. _*The tyre had been filled with compressed air instead of non-flammable nitrogen.*_ CASA airworthiness directive AD/WHE/4 mandates nitrogen inflation of tyres for aircraft with an MTOW of more than 5700kg, as well as for smaller aircraft if their tyres are speed-rated to more than 266km/h. The reason for using nitrogen is to eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile isoprene gas (produced by severe heating of the tyre)causing an explosion.




_*The concensus is that the tyre was wrongly filled, caused an explosion which downed the aircraft*_


Please feel free to disbelieve, but if you wish to continue to challenge this, then you need to take it up with the investigators


----------



## classic33 (8 May 2016)

Reading those, it was the brakes dragging that caused the overheating. 
Causing the tyre to explode.
Fueling the fire, nitrogen wouldn't have fueled any fire.


----------



## Ajax Bay (8 May 2016)

Thanks to @Ffoeg :
"O2 does have a greater molecular weight (32) than N2 (28), but O2 is actually smaller in size. Thus, O2 fits through the relatively tight passage
ways between polymer chains in the rubber more easily than does N2. The difference is size between O2 and N2 is very [very, very] small, only about 0.3 times 10 to the -10th meters (0.00000000003 meters). O2 "permeates" approximately 3-4 times faster than does N2 through a typical rubber, as is used in tires, primarily
because O2 has a slightly smaller effective molecular size than does N2." (The O2 molecule is 'narrower' - see @Ffoeg 's link in post #27 for more, much more.)


----------



## Brandane (8 May 2016)

classic33 said:


> Reading those, it was the brakes dragging that caused the overheating.
> Causing the tyre to explode.
> Fueling the fire, nitrogen wouldn't have fueled any fire.


The exploding tyre also ruptured hydraulic lines and fuel lines, and severed electrical cables. The fuel ignited and from that point they were in trouble.


----------



## classic33 (8 May 2016)

Brandane said:


> The exploding tyre also ruptured hydraulic lines and fuel lines, and severed electrical cables. The fuel ignited and from that point they were in trouble.


An exploding tyre filled with an inert gas wouldn't have fuelled the fire though.
Chances are it would explode, whatever you gas(es) you used. All other things being equal.


----------



## Brandane (8 May 2016)

classic33 said:


> An exploding tyre filled with an inert gas wouldn't have fuelled the fire though.
> Chances are it would explode, whatever you gas(es) you used. All other things being equal.


Yebbut .... I don't think in this particular case the oxygen in the tyre would have contributed much to the fire. Leaking aviation fuel and severed electrical cables don't need much encouragement .


----------



## Ajax Bay (8 May 2016)

classic33 said:


> Chances are it would explode, whatever you gas(es) you used. All other things being equal.


The overheated tyre exploded BECAUSE O2 was present inside the tyre (ie 20% of the gas inside the tyre). If the gas inside the tyre had been N2 (100%) the explosive reaction would not have occurred. As @Cunobelin has quoted:
"The reason for using nitrogen is to eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile isoprene gas (produced by severe heating of the tyre) causing an explosion."


----------



## newfhouse (8 May 2016)

screenman said:


> Are the comparable in initial ticket price? I only ask as next year I intend to cycle a bit in other countries.


It cost me £28 on Easyjet CPH - LGW. I put the bike in a clear CTC bike bag, no damage. Good value, I thought.


----------



## classic33 (8 May 2016)

Ajax Bay said:


> The overheated tyre exploded BECAUSE O2 was present inside the tyre (ie 20% of the gas inside the tyre). If the gas inside the tyre had been N2 (100%) the explosive reaction would not have occurred. As @Cunobelin has quoted:
> "The reason for using nitrogen is to eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile isoprene gas (produced by severe heating of the tyre) causing an explosion."


It wasn't the tyre that got hot though, it was the wheel onto which it was fitted. Caused by "a dragging brake".


----------



## DaveReading (8 May 2016)

Cunobelin said:


> Google Mexicana Flight 940
> 
> One of the key findings as the cause was one of the wheels in the central undecarriage containing pressurised air as opposed to Nitrogen
> 
> If you still don't believe, take it up with the official investigators



Without seeing the investigation report, rather than Wikipedia's misquoting of it, it's not possible to say whether the tyres being filled with air was the cause of the accident or simply a contributing factor (aircraft tyres filled with 100% nitrogen also explode from time to time, usually as a result of brake overheating, and sometimes result in collateral damage, so nothing new in that).

Either way, no investigator would make reference to the centre undercarriage on a Boeing 727, as there is no such thing, which màkes one wonder what else may have been lost in translation between the original investigation report and Wikipedia's account of it.


----------



## Alembicbassman (9 May 2016)

Letting the air out makes the bike lighter so they can add a few grams of cargo


----------



## mustang1 (12 May 2016)

It was my first flight with any bike so deflated the tires. Upon arrival at the hotel I popped into the LBS and got a hundred psi into the tires. I'm happy enough.


----------



## Drago (11 Apr 2017)

Its to stop people from smuggling air around the world.


----------



## Phaeton (11 Apr 2017)

midliferider said:


> I did this first time I took the bike on the plane. Now I don't do it at all. They won't ask you any questions as long as you have paid the exorbitant fee that they charge.


I've never deflated my tyres & I've never paid to have the bike onboard it's always been classed as sporting goods & included in the cost.


----------



## Globalti (11 Apr 2017)

An aircraft hold is held at around 10,000 feet pressure so as to ensure the people inside it have enough oxygen to live.

Do the competitors in a bike race deflate their tyres when they cross a 10,000 foot col in the Alps? No they don't.
Do the tyres burst? No they don't.
Would a tyre bursting in the hold endanger an aircraft? No it wouldn't.
Do pressurised aircraft fuselages have unpressurised holds? No they don't, the floor would explode downwards.


----------



## Yellow Saddle (11 Apr 2017)

Globalti said:


> Do pressurised aircraft fuselages have unpressurised holds? No they don't, the floor would explode downwards.


In support of this sentence, you forgot to mention that pets and livestock are routinely transported in holds. I believe on a certain Irish airline they even crate humans for transport in the sub-economy section.


----------



## Globalti (11 Apr 2017)

On overheating tyres, there's a video on YouTube that shows a brake test on a 747 where the brake discs can be seen glowing red hot. Once the aircraft comes to a stop the tyres automatically deflate so as to prevent an explosion. A tyre explosion releases a huge amount of energy and can cause damage to systems that can cause a fire, as explained by others in this thread. A woman was killed by a car tyre exploding when she held it on her lap in a small car: http://news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/8600833.stm

Blind, unquestioning obedience to idiotic rules really boils my wee; I will challenge anything I see as jobsworth idiocy. Unfortunately jobsworths have to be given rules because when they are allowed to exercise judgement they often get it wrong, due to being idiots.


----------



## Milkfloat (11 Apr 2017)

One of my favourite vids - the money shot is at about 25 seconds.



and these ones are where people got a little hurt.


----------



## Ajax Bay (17 Apr 2017)

Drago said:


> Its to stop people from smuggling air around the world.


Holy (11 month) thread resurrection, Batman (@Drago )!


----------

