Cycling UK Forum

simonhill wrote:
The reason I don't like doing it, landsurfer, is because it can damage sidewall and tube. The bike can be sitting on the flats for a long time, maybe dropped on them, etc. My tyres have thin, flexible sidewalls.

Please i don't want to sound flippant but just get some suitable tyres fitted ......
You don't use a helmet cam do you .... ????

thirdcrank wrote:It's a while since this recurring topic surfaced. Can somebody remind me where a plane's own tyres fit into this?

Their designed to cope with it ....
It's called Engineering.

cycleruk wrote:

meic wrote:The most pressure increase that the tyre can possibly experience is another 15psi and that is in the vacuum of deep space!
So it is unlikely to exceed the max rated pressure of the tyre/wheel assembly in a cargo hold rapid decompression.

If "deep space" is a vacuum then how come the earth's atmosphere, at a higher pressure, doesn't get sucked off into it.

That'll be gravity

I am pretty sure that when they designed the aircraft tyres, the exposure to a 15psi drop in external pressures was so low down their list of design criteria that it wasnt even on it!

tatanab wrote:

thirdcrank wrote:It's a while since this recurring topic surfaced. Can somebody remind me where a plane's own tyres fit into this?

Plane tyres are typically around 200 psi, therefore the percentage difference of one atmosphere is about half the percentage difference of a pedal cycle tyre at 100 psi which might or might not (according to manufacturer's spec) be specified to 115ps. Perhaps the baggage handlers do not want to be checking the tyre pressures of every pedal cycle they carry, so it is easier to say "let them down". I always let mine down, not fully, but with enough remaining air that they hold shape yet collapse easily under pinching fingers. Some wheel chairs and children's prams etc have pneumatic tyres - I wonder if the handlers bother to check them.

This is just a ramble to introduce what tyre pressures are used by planes, and with no scientific or logical reasoning for needing to deflate pedal cycle tyres.

fastpedaller wrote:

cycleruk wrote:

meic wrote:The most pressure increase that the tyre can possibly experience is another 15psi and that is in the vacuum of deep space!
So it is unlikely to exceed the max rated pressure of the tyre/wheel assembly in a cargo hold rapid decompression.

If "deep space" is a vacuum then how come the earth's atmosphere, at a higher pressure, doesn't get sucked off into it.

That'll be gravity

Careful .... it appears someone doesn't believe in space ....... or gravity ...... or science ... or sanity

meic wrote:I am pretty sure that when they designed the aircraft tyres, the exposure to a 15psi drop in external pressures was so low down their list of design criteria that it wasnt even on it!

Ditto cycle tyre manufacturers.

Cabin pressure in an aircraft will vary with the altitude it is flying at.

Aircraft holds are pressurised to the same pressure as the cabin.

On the aircraft I fly, the maximum cabin pressure is 8.4psi, which is equivalent to being at 8000' above sea level.

So the bike tyres are not going to burst on a normal flight.

Even if we lost all pressurisation, as has been said before, the increase in tyre pressure would only be 15psi. I would expect the tyre to withstand that or else we would be getting punctures all the time due to pot holes and bumps through normal riding.

If you want to see a good example of the effect of cabin pressure, drink a bottle of water empty and reseal it before the aircraft starts to descend. After landing it will be quite crumpled by the increase in pressure.

landsurfer wrote:

simonhill wrote:
The reason I don't like doing it, landsurfer, is because it can damage sidewall and tube. The bike can be sitting on the flats for a long time, maybe dropped on them, etc. My tyres have thin, flexible sidewalls.

Please i don't want to sound flippant but just get some suitable tyres fitted ......
You don't use a helmet cam do you .... ????

My tyres are very suitable. Suitable for long distance touring, which is mainly what I do. Foldable Marathon Supremes. Just finishing 2,400 kms in Japan.

I don't wear a helmet, unless forced to by the law, eg Oz or NZ.

I have also seen many wheelchairs delivered from the aircraft hold to the aircraft steps. None of them needed the tyres pumping up before being used.

Daniel Fox wrote:I have also seen many wheelchairs delivered from the aircraft hold to the aircraft steps. None of them needed the tyres pumping up before being used.

We flew from Edinburgh to Beziers on Ryanair in september. At the oversize baggage counter in Edinburgh, the attendant brought up the old chestnut of "are the tyres deflated?", I said they weren't, he then insisted that they be deflated, I asked him to call the airline or his manager and check, he made the call, and got told to allow the bikes through with the tyres as they were. They were still in one piece and inflated when we arrived in Beziers.
I also asked him if they asked wheelchair users to deflate their tyres, to which he replied that they did! I didn't believe him.

Daniel Fox wrote:I have also seen many wheelchairs delivered from the aircraft hold to the aircraft steps. None of them needed the tyres pumping up before being used.

Many wheelchairs (I think possibly all of those I know) use solid tyres - because the costs of a puncture are so severe. Additionally the comfort is acceptable at low speeds...

Powered chairs are different, although I'd expect that to make the flight really complex...

If say for some reason the pressure drop did burst the inner tube what's the worst that could happen? When I've had inner tubes burst its been loud but totally benign

PrestonCyclist wrote:If say for some reason the pressure drop did burst the inner tube what's the worst that could happen? When I've had inner tubes burst its been loud but totally benign

..............but, but, bicycles are dangerous, everyone knows that.

tatanab wrote:This is just a ramble to introduce what tyre pressures are used by planes, and with no scientific or logical reasoning for needing to deflate pedal cycle tyres.

I read somewhere that there is a shred of logic behind the rule. BIG tyres (tractors, building plant, etc) can be inflated to as low as 10 PSI. An extra 15 PSI obviously becomes a big deal, something for which the tyre probably isn't designed. And a tyre of that size exploding in the hold has potential to cause catastrophic damage to the plane, so it's essential that they're deflated.

So airlines have a rule in large letters saying 'TYRES MUST BE DEFLATED' and then in very small print ('except bicycle/wheelchair tyres'). And even if it must be staggeringly rare for that type of vehicle to travel by plane and practically never on the type of planes we take our bikes on, we get caught out by somebody remembering the large print bit of the rule.

I guess car tyres come somewhere in between, and cars are flown around slightly more often. An overinflated tyre would be at risk with an extra 15 PSI, so I guess it matters for them as well.

Personally I find the issue annoying because we fly with the tandem which has 1.75" tyres at 80 PSI. That's quite a lot of inflating to to with a handpump.

if anyone is worried about lightweight tyre/rim damage when deflated, might I suggest that a short length of pipe lagging might be zip-tied to the bottom of the wheels (which are themselves zip-tied to prevent rotation)..? If this is done, the bike can be stood on its wheels (even if it can't be wheeled along) without such risk of tyre/rim damage.

Re-usable zip-ties make this sort of thing easy enough to do.

cheers