One for the physicists out there!

[ForkTailedDrKiller]

I just bought a folding electric bike to stick in the luggage compartment of the Bonanza.

If the tyres are inflated to 65 psi at sea level, what's going to happen when I climb to 10,000 ft?

FTDK

[Yakka]

If what you are asking is, Will the tyres pop? Then the answer is no.

Cant be bothered going through the maths on that one but, they have an optimum pressure on the side of the tyres of say 65psi - This is not the maximum that it can be inflated to. They are designed to take extra pressure in the form of shock when the tyre is in use. If this was really an issue then car tyres would have the same problem when driving up large mountains etc.

I wouldn't be to concerned

[Ozgrade3]

I;d like to kow how thw space shuttle tyres hold together. i hear they are pumped up to some fantastic preasure then manage to stay intact in vacu,e + heat and cold of space the heat of re-entry. Now thats a tyre. Would hate to see te cost tho..

[Chimbu chuckles]

Probably because they are filled with nitrogen...which doesn't expand or contract with changing temperature.

FTDK...a complete non issue...but you could get them filled with nitrogen too if you wish...I had new rubber put on my Pajero recently and they filled them with nitrogen..and charged me $30...despite the fact I said air would be fine

[Andy_RR]

It's the differential pressure that inflates a tyre, not the absolute pressure. Climing to FL200 will add another 0.5Bar to the effective inflation pressure, so at 65psi that's only another 10% or so. Not much really.

Re: Space Shuttle tyres, if they are already at huge pressures, then putting them into a vacuum is only going to add 1Bar to the inflation pressure - didly squat in the scheme of things.

A

[YesTAM]

Errrrrrr.....Chimbu, Nitrogen follows the ideal gas law PV=nRT reasonably closely like most other gases at the pressures and temperatures you are talking about. The advantage of Nitrogen is that it is INERT.

Furthermore, since sea level pressur eis about 15 psi, the most pressure differential you are going to get is....15 psi in vacuum.

[Creampuff]

Do you worry about the Bonanza's tyres when you climb to 10k?

[ForkTailedDrKiller]

Creampuff

That's a really good question that only occurred to me after I put this post up.

Thanks for all the responses. It would appear to be a non-issue!

FTDK

[Lefthanded_Rock_Thrower]

From memory, anything inflated over 40psi is a DG for that reason, buy a pump.

[Capn Bloggs]

Chimbu,
I'm shocked! I used to believe everything you said. Now I'm not so sure!

[ForkTailedDrKiller]

Ah ha! The plot thickens! I detect a note of dissent creeping into the thread (eg a rock thrown left handed!).

Maybe I will just have to let the scientist in me have his head. I'll put the bugger behind a secure cargo net and take it to 10k to see what happens.

FTDK

[bushy]

Measuring pressure

That's an interesting one. I remember the medics being somewhat puzzled when they tried to take patients' blood pressure in flight.

[Miraz]

Most tires are filled with compressed air, which when dry consists of about 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases by volume.
Water vapor (humidity) can make up as much as 5 percent of the volume of air under worst-case conditions.
Filling your tires with nitrogen mainly does two things: it eliminates moisture, and it replaces skinny oxygen molecules with fat nitrogen molecules, reducing the rate at which compressed gas diffuses through porous tire walls. Removing moisture is a good thing as the presence of moisture means that compressed air does not follow the ideal gas law as the temp passes through 100 degrees.
That means, theoretically at least, that a tire filled with nitrogen retains optimal pressure longer and provides more predictable behaviour when worked hard.

[Seabreeze]

here are my thoughts
If msl pressure is P= 14.7 psi, and at 10,000ft P=~9.8psi (approx 2/3 atmosphere), then the tyre pressure relative to air at 10,000 ft will be
65+(14.7-9.8) = 69.9psi.
This should not be too much to blow your tyre.
[This assumes your tyre does not expand during ascent]
seabreeze

[Peter Fanelli]

You will of course make sure the batteries are disconnected and packed in a suitable container and the appropriate notifications are made to the captain, right?

[ForkTailedDrKiller]

PF - Its a bit hard to figure if your post in "tongue in cheek" or not.

The battery in my folding electric bike is an overgrown sealed Ni-Hydride unit like the one in my computer.

I guess as I am the Captain, I can consider myself to be appropriately notified!

If anyone is interested, the electric folding bike is a Sherpa Mk3. Weighs 21 kg, incl battery. I took it for a lap yesterday. Sits on 25 km/hr on the flat, running on just the lekky motor (I am 90+ kg). If I give it a bit on a helping hand by peddling it will run up over 30 km/hr. Has a range of 30 km on battery power only - more if you peddle a bit. I am pretty impressed with it.

Why did I get an electric folding bike? Cause I am fed up with places like Cairns and Rocky where I am forced to park the Bo on the opposite side on the field from the airline terminal and then have to get a taxi to and from the terminal to collect and return a rental car.

FTDK

[Chimbu chuckles]

Of course you're right re nitrogen

Someone, maybe an engineer, explained to me filling jet aircraft tyres with nitrogen for the reason I have stated YEARS ago and I just didn't think it through and the Tire mart fella mumbled something along those lines a few weeks ago and it just washed past me untested...everytime that happens I live to regret it

The simplest answer is nearly always correct...just the buffer built in for pot holes more than covers any increased pressure differential from climbing a mere 10000'...or even 30.

Bloggs...sorry

[Miraz]

A few gotchas for these batteries:-

• Keep them cool - at temps over 60 degrees they can release gases including hydrogen
• If you use them at temps over 40 degrees then they make leak - most NiMh batteries are highly corrosive
• Over charging can cause them to catch fire - even some time after they have been disconnected from the charger

And you were worried about the tyres?

Starting to make pedal power sound attractive...