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Altitude and tire pressure? Altitude and tire pressure?
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Photo by Marc Gibaud, Clouds on Tres Cerros and Mount Fitzroy, Argentinian Patagonia

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Photo by Marc Gibaud,
Clouds on Tres Cerros and
Mount Fitzroy, Argentinian Patagonia



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  #1  
Old 6 Jan 2016
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The question was about unusual tyre pressure readings, not how the tyres acted on the road.
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Old 6 Jan 2016
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Quote:
Originally Posted by Tim Cullis View Post
The question was about unusual tyre pressure readings, not how the tyres acted on the road.
Hey Tim, News Flash! These two points are LINKED. You can't talk about one without mentioning the other. Pressures affect the ride and the ride (and bike) may need pressure adjustment depending on what the pilot "feels". The Pilots perceptions are KEY to it all.

If my bike "feels" weird (what ever the hell that means!) I might get off and put a gauge on the tires ... or maybe use my EYES and notice I've got a flat.

Seat of the pants "feel" is our last best hope for survival on a bike!
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  #3  
Old 6 Jan 2016
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I understood that moisture in air causes no significant departure from the ideal gas law under normal practical driving conditions. When that is pointed out, all sorts of other reasons surface like causing rust on the rims or the tyres rot out on the inside which in itself is a load of rot or it rusts the steel cords or... or... .
The bit about using nitrogen in normal car and truck tyres gets shot down every time it is raised so I don't know why it can't stay dead.

As for the actual pressure inside a tyre. Couldn't you make an argument that if you go up in altitude, the air pressure is pushing less on the outside of the tyre so the tyre becomes effectively over inflated - but high altitudes are usually associated with lower ambient temperatures which reduce the running pressure, thus mitigating any altitude effects.

Then again ....

or maybe even .....

Just ride.
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Old 6 Jan 2016
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Originally Posted by Tony LEE View Post

As for the actual pressure inside a tyre. Couldn't you make an argument that if you go up in altitude, the air pressure is pushing less on the outside of the tyre so the tyre becomes effectively over inflated - but high altitudes are usually associated with lower ambient temperatures which reduce the running pressure, thus mitigating any altitude effects.

Then again ....

or maybe even .....

Just ride.
Excellent point....

We need a official science boffin to solve this for us
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Old 6 Jan 2016
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Originally Posted by *Touring Ted* View Post
Excellent point....

We need a official science boffin to solve this for us
They are too busy with the global/climate warming/change/cooling conumdrum.

Boyle's law applies though.

"the law is accurate enough to be useful in a number of practical applications. It is used, for example, in calculating the volume and pressure of internal-combustion engines and steam engines".
From Boyle's Law - HowStuffWorks
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Old 6 Jan 2016
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I had the three main gas laws—Boyle's, Charles' and Henry's—drilled into me from my days in BSAC (scuba).

Gases heat up as they are being compressed, one of the two reasons for immersing scuba tanks in water whilst being filled (the other being to mitigate the effect should a bottle fail). Gases rapidly cool when being deflated which is why those tiny CO2 canisters used to inflate a tyre have a mesh cover—the canister drops to subzero temperature.

Charles' law states the pressure varies directly in proportion to the temperature (°K) which is why you are told to measure tyre pressures when the tyre is cold, but many people don't realise this. When the hot tyre cools the pressure drops and the tyre is under inflated.

On another thread here or maybe another forum, someone was asking me how I was getting on with mousses in my KTM 690R (supposedly the equivalent of 0.9 bar or 13 psi). I had to say that I couldn't actually notice any difference between my 690 in Spain with mousses and my 690 in the UK with standard inner tubes which are probably at 2 bar.

So as Ted says, just keep riding.
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Last edited by Tim Cullis; 6 Jan 2016 at 11:52.
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Old 6 Jan 2016
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There is one situation where tyres need to be inflated to a non-resting value and that is when the vehicle is stored in a heated garage but will be operated in a very cold environment. I guess if it was stored in airconditioned garage but operated in summer desert conditions a similar allowance would need to be made.
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Old 6 Jan 2016
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Originally Posted by Tim Cullis View Post
I had the three main gas laws—Boyle's, Charles' and Henry's—drilled into me from my days in BSAC (scuba).
With all 3 you can have some fun in the global warming debate.
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