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Old 2019-05-24, 06:25 AM   #1
Vogelfrei80
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Helium in a foss tube will leak?

Dumb question?
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Old 2019-05-24, 06:56 AM   #2
finnspin
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Probably.

Also yes, since it will provide very small weight savings for the price and effort. You can either do the math yourself or google it to find someone that has done it already. Bottom line is, you probably wouldn't be able to measure the weight difference if you put the unicycle on a scale afterwards.
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Old 2019-05-24, 07:26 AM   #3
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Helium leaks very easily. I doubt it would stay inflated for long.

I assume you are thinking of saving weight by using Helium in the tube.

Air has a standard density of about 1.2 kg per cubic metre while Helium is about 90 grams. Raised to four atmospheres (60 psi) gauge, amounts to a difference of about 5.5 grams per litre. (Assuming all the air was removed, we multiply by five rather than four since the first atmosphere in the tube doesn't register on the pressure gauge.)

A big 36 inch tyre with say a 7.5 cm (3 inch) wide circular cross-section would have a volume of about twelve litres so you would be saving about 65 grams of mass by using Helium instead of air.

Someone might want to check my logic and maths.
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Old 2019-05-24, 07:46 AM   #4
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Quote:
Originally Posted by OneTrackMind View Post

Someone might want to check my logic and maths.
I was bored too and did the math with very similar numbers, and got 68 grams of weight savings. More than I expected, if you have a pretty accurate scale you might actually be able to measure that. (most home scales are accurate to 0.1 kg).
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Old 2019-05-24, 08:43 AM   #5
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Thermoplastic inner tubes (which I think FOSS tubes are) should, I think, stay inflated with helium longer than butyl tubes. One of their advantages is that they keep air pressure better so presumably this makes them less permeable to helium as well. Quite how they would compare to the mylar foil used for helium balloons I have no idea.

Some info on thermoplastic tubes:

http://www.polyurethanes.basf.de/pu/...h_applications

Quite whether it is a good idea or not, looking at more aspects than just weight saving, is explored (somewhat tongue-in-cheek) here:

https://www.cyclist.co.uk/in-depth/7...es-with-helium
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Old 2019-05-24, 11:01 AM   #6
Vogelfrei80
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I was just wondering about the rotational weight saving for a light road 3.8 fat tire with a fat foss tube.

Not meant to improve overall weight, intersted only in the rotational mass.
Not interested in butyl tubes, nor in tubeless setup, nor in heavy spokes or rim...

Why not a fat termoplastic tube filled with helium?
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Old 2019-05-24, 11:12 AM   #7
Vogelfrei80
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Quote:
Originally Posted by DrD View Post
Thermoplastic inner tubes (which I think FOSS tubes are) should, I think, stay inflated with helium longer than butyl tubes. One of their advantages is that they keep air pressure better so presumably this makes them less permeable to helium as well. Quite how they would compare to the mylar foil used for helium balloons I have no idea.

Some info on thermoplastic tubes:

http://www.polyurethanes.basf.de/pu/...h_applications

Quite whether it is a good idea or not, looking at more aspects than just weight saving, is explored (somewhat tongue-in-cheek) here:

https://www.cyclist.co.uk/in-depth/7...es-with-helium
The last link seems to tell me: helium is not so important... but if you use a big air tire... made to be ride not at low psi... not in a butyl tube... you could save the weight in the most important part a uni...

Can you help me with the math for a 3.8" inflated at 40PSI?
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Old 2019-05-24, 01:19 PM   #8
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Quote:
Originally Posted by Vogelfrei80 View Post
Can you help me with the math for a 3.8" inflated at 40PSI?
The volume of the tube is its cross sectional area times the average distance around the tyre measured in centimetres to give a result in cubic centimetres which is the equivalent of a millilitre. Air weighs about 1.2 grams per cubic centimetre. Multiply this by the number of atmospheres pressure plus one.

The cross-sectional area depends on the rim as well as the tyre and there are irregularities but it approximates a circle with a diameter equal to the maximum width of the mounted tyre.

The area is pi times half the width of the tyre squared.

The length is the pi times slightly less than the nominal wheel diameter. This is best measured in the individual case as we know that tyre sizes are just numbers.
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