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john alexander
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Post by john alexander » 01 Nov 2004, 19:38

Hi my son in the RAF tells me that tyres on jets are filled with nitrogen and if you do the same on car tyres they will run cooler,and nitrogen is better for the rubber.Comments please john.

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Post by oilyspanner » 01 Nov 2004, 19:40

Was told the same thing a few weeks ago, apparently it has a lower coefficient of expansion too, supposed to improve tyre life and fuel consumption! usually costs about a fiver, have not tried it yet.

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Post by Kowalski » 01 Nov 2004, 20:27

Nitrogen may be better for the rubber on the inside of the tyre, but the rubber on the outside will still be exposed to the air. Have you ever noticed how the inside of the tyre doesn't age in the same way that the outside does? Something to do with exposure to sunlight...
Air is made of various gasses, Nitrogen (78%), Oxygen (21%), Carbon dioxide (0.04%) the remainder being inert gasses and water vapour. The component of air that causes expansion problems is the water vapour content, theoretically, if you could use dry air that would be as good as the nitrogen from an expansion point of view.
As for tyres running cooler with nitrogen in them, since it has a 'lower thermal expansion' you are able to run a higher cold tyre pressure with nitrogen since it won't expand as much and produce a peak hot pressure as air would.

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Post by Mads » 02 Nov 2004, 02:01

I agree with Kowalski that sunlight is probably the worst tyre killer.
The 'lower thermal expansion' bit is however not very likely in my oppinion, as the behaviour of fairly inert gasses under moderate pressure, e.g. Oxygen and Nitrogen, are idential, i.e. Pressure is proportional to the absolute temperature measured in e.g. degress Kelvin (0°C = 273Kelvin, 100°C =373Kelvin). My guess is, that jets tyres are filled with nitrogen in order to avoid condensation of water vapour (formation of ice inside the tyres) at the extreeme temperatures at 12000ft.
Nitrogen is probably also better for the tyre material, as oxygen, given time, will attack rubber making it hard and brittle. This process is accelerated by heat and pressure (and UV-light), but I doubt it will be a problem for the average motorist.
My guess is that tyre temperature is more or less determined by the friction generated when the tyre roles on the road balanced against the heat removed by cold air sweeping the tyre. In this balance the heat capacity of the compressed air in the tyre is very insignificant, and henc it is very unlikely that a Nitrogen tyre would run colder than an "air" tyre.
All in all my choise will be to use my fiver on a better engine oil or maybe as an investment in future spares: A few flowers for he misses.

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Post by jeremy » 02 Nov 2004, 02:25

Tubeless tyres have a thin layer of rubber on the inside to seal them. This doesn't form part of the structure and so if it perishes a little on its surface it won't affect the structual strangth of the tyre. Having said that I have never seen any perishing of that layer.
Of course the air inside the tyre is captive and so if any perishing takes place it will only happen while there are active compounds available and will stop when they have been used up.
I have seen various attempts to market nitrogen for tyre inflation, based on the usual scare tactics but they seem to dissappear rapidly. the tyre manufacturers have landed us with strange things over the years, the last being the safety tyre that needed a metric diameter rim (some early BX had them I believe. They don't seem to be trying to make us use nitrogen (supplied by them no doubt!)
Checking pressures on a nitrogen tyre will be a real problem unless you go to a nitrogen station.
I agree with mads - better uses for the money!

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Post by Kowalski » 02 Nov 2004, 15:35

Formula one teams use Nitrogen in the tyres of their F1 cars, the reason given was that air doesn't expand predictably with temperature because the water vapour content varies.
Dry gases will behave more like an ideal gas than gases with a water vapour component, since the water vapour will condense out under pressure and evapourate again under temperature.

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Post by tomsheppard » 02 Nov 2004, 15:49

And dry nitrogen is cheap, as well as being inert.
Use Air. This nitrogen thing is just the same BS as paying £30 a yard for speaker cable instead of using 13A flex to do the job.

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Post by NiSk » 02 Nov 2004, 16:34

No no Tom!
Use cooker connecting wire (preferebly single stranded) - it's much better than 13A flex.

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Post by tomsheppard » 02 Nov 2004, 16:42

single stranded wire hardens and breaks- besides, I've got a gas cooker!

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Post by bernie » 02 Nov 2004, 16:58

And gas cookers make for better toast

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Post by beezer » 02 Nov 2004, 17:08

The topic seems to have digressed but speaker wire depends on power output and length of cable run. You wouldn't use lighting flex to jumpstart your engine just as you wouldn't be wise to use too low a rating flex to power speakers. Leave all the 'oxygen free' arguments to the audiophiles. '13 amp' mains flex will not necessarily handle 13 amps. My PA rig has a 3 kilowatt output and I stick to heavy duty speaker cable designed for the job. For my small gig set up I would be quite happy to use mains flex if it was 4 core.
One more thing, how do you do a roadside top up with a nitrogen filled tyre?

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Post by Kowalski » 02 Nov 2004, 17:15

You use your nitrogen bottle silly!

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Post by beezer » 02 Nov 2004, 17:18

But that is full of helium in case I get stuck in a flood.

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Post by tomsheppard » 02 Nov 2004, 17:36

13A wire will carry 13A at up to 250 Volts ac. Ignoring HF skin effects which all occur above audio frequencies, there are very few systems that need more than this. A 3 KW output (Presumably RMS per Channel?) would be happy to run on 13 Ampere cable. As a professional broadcast audio engineer, I wouldn't need anything more than that. After all, your 3KW won't be feeding just one drive unit, will it?

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Post by ItDontGo » 02 Nov 2004, 18:20

I read a paper once (well read the summary the rest was too boring) and it concluded there was a slight effect on higher audio frequencies with crap cable. It was due to the current in the centre of the wire building up quicker than at the outer part. I doubt anyone would really notice unless they had two units together and even then they would be hard pushed.
What kind of speaker can handle 3 kilowatts? If it was a dummy load that would be over 27 amps. The ouput power on audio equipment could mean anything. Not many people give RMS because thats the true figure. Why would they when they can say they have 4 times that by quoting the peak music power output.
If you had a 3kw amplifier would the power lost in the cable mean that you couldn't hear anything? After all you know 2.8kw just aint load enough is it? Although if 200w was going into the cable then it might get a bit hot.