Helium in tyre...

What volume of air do you think would be in the average Gazz 24" x 3"? Or more to the point (and saving me a lot of thaught and time :)), how much lighter would a unicycle be that’s fitted with a Gazz filled with helium? Is helium the lightest available gas?

What if you made a uni that had some sort of really light gas in the tyre, frame, cranks, and seat?


Are there really unicycles or bikes with light gases in the tires?

where did you get that cartoon???

I think that Hydrogen is a tiny bit lighter, but by a very small amount. Not to mention that it’s extremely flammable, so I wouldn’t recommend it.
I’ve never heard of putting helium in tires before. I always inhale helium whenever I can get my hands on some. But then, that was just from balloons. I’m assuming you mean like a tank of it.



I love the cartoon Andrew and thanks for the website too.
That made me laugh today. I love a good laugh, Gags and a good Jokes too.


most bicyclists that go for the hour record have helium filled tyres…

Good thinking James, why not fill your lungs with the stuff too, not only will it make your voice comical to others, but you’ll be lightning fast too with you saving all that wieght that heavy air would take up in your lungs. I can see it now all the top athleats at Unicon sucking down helium ballon’s before each race to get that edge…


I think you’d have to do a lot of refilling. The molecules are pretty small, and eventually pass through the average elastic, where air will not. Hence the fact that helium balloons lose their bouyancy so quickly unless coated inside with special goop. Maybe Slime plus helium would work. But for anyone smart enough to want to shave off that minimal amount of weight, better to just leave their shorts behind so others can quickly place the appropriate label upon them.

Hmmm…I wonder if we could have an hour record in unicyling too?

Conceivably one could do 25-35k in an hour on a unicycle in a velodrome on a Coker with aero bars and helium filled tyre. That would be about half the bicycle hour record (49.???km after they downgraded it). That would be so cool!

I think hydrogen is approximately half as heavy as helium. Hydrogen has only one proton; helium has two. I can’t remember about how many neutrons there are in each.

Hydrogen is explosive, rather than inflammable. A subtle difference, but important in some circumstances. :astonished:

To calculate the volume of air/helium in a tyre:

You need to think of the innter tube as a cyclinder.

Calculate the cross sectional area. That is Pi x (radius squared)

That’s the radius of the cross section of the tube. So if the inflated tube is, for example, 3 inches across, the radius is 1.5 inches and you square that and get 2.25.

Pi is 3.14, so you multiply 3.14 X 2.25 = 7.065 inches.

Now you need to calculate the length of the cyclinder. That will be very roughly the circumference of the wheel. In fact it will be a bit less than the circumference of the rim of the tyre, and a bit more than the circumference of the rim. What you could do is measure the diameter of the rim, measure the diameter of the inflated tyre, and average the result.

e.g. Rim 26 inches, tyre 28 inches, average 27 inches.

The circumference is Pi x diameter
3.14 x 27 inches = 84.78 inches

Now the voulme of the tube is the lenght of the cylinder, multiplied by the cross sectional area:

84.78 x 7.065 = 599 cubic inches.

But to find how much air/helium the tube contains, you need to multiply the volume by the pressure in Bars/Atmospheres.

1 Bar is approximately 14 pounds per square inch. So if the tube is inflated to 56 psi, that’s 4 Bars, so the tube contains the equivalent of 599 x 4 cubic inches of air/hydrogen. Say 2,400 cubic inches.

Now all you need to do is find the weight of air/helium per cubic inch.

Remember to use the same units all the way through: either inches or centimetres.

Personally, I shall carry on using air and not worrying.

Hydrogen: one proton, no neutrons (unless you have deuterium (spllng?) which has one proton and one neutron but is still hydrogen - chances of finding an atom of deuterium in pure hydrogen aprox 1%)

Helium: two protons, two neutrons.

Relative atomic masses: H 1
He 4

Therefore Hydrogen is a quarter of the mass of helium.

However u dont want to use hydrogen in ur tyre, it could explode. If you had pure hydrogen there would be no oxygen to burn, but get a slight leakage of oxygen into the tyre and the tiniest static spark would send you flying!!

You could include a BBQ ignition or an electric piezo ignition, and ignite your tire just before heading for the finish line of your record breaking burst. Maybe being sent flying could give you the edge over the competition who are using heavy helium tires. People would say “Look at her/him go, s/he is on fire!”

LOL! unfortunately it would wreck the uni and probably burn the skin off ur buttocks!! Or melt ur lycra shorts to ur arse!

O yeah, me being thick I forgot Helium is monatomic (one atom in a molecule) whereas hydrogen is diatomic. Ive forgoten, but would this mean it is only half the weight at the same pressure or would it still be a quarter? (i was away from school when we were doing moles and stuff)

Anyone care to answer??


Re: Helium in tyre…

This has come up a few times on the list in the past few years.
You will save more weight by doing a few other things first.

Here are a few suggestions of reducing the overall weight.

get rid of the tool kit, the camel back and excess clothing.

try to lighten up other areas - cranks, clamps and seat and post.

Cutting off any excess seat post length will probably save more weight than
fiddling around with expensive gasses will.

For the ultimate in light weight riding you would need buy a sexy Roger
Davies carbon fibre uni, put hydrogen in the tyre and ride it nude. Shaving
off all your hair could also save a little extra weight.

Wayne van Wijk

“andrew_carter” <andrew_carter.nltzm@timelimit.unicyclist.com> wrote in
message news:andrew_carter.nltzm@timelimit.unicyclist.com
> What volume of air do you think would be in the average Gazz 24" x 3"?
> Or more to the point (and saving me a lot of thaught and time :)), how
> much lighter would a unicycle be that’s fitted with a Gazz filled with
> helium? Is helium the lightest available gas?
> What if you made a uni that had some sort of really light gas in the
> tyre, frame, cranks, and seat?
> Andrew
> ±---------------------------------------------------------------+
> | Attachment filename: cartoons - helium.gif |
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> andrew_carter - Temporary Onza-ist…
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> andrew_carter@mail.com
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> ------------------------------------------------------------------------
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> View this thread: http://www.unicyclist.com/thread/25216

Re: Helium in tyre…

A clarification…

> For the ultimate in light weight riding you would need buy a sexy Roger
> Davies carbon fibre uni,

I am referring to the sexiness of the carbon fibre unicycle, not that of
Roger Davies.

Wayne van Wijk

Re: Re: Helium in tyre…

Do they actually weigh much less than a lightweight steel unicycle would? I reckon they’re mainly only cool because of the ‘high tech material thing’ rather than actually being any better than a well made steel / alu / ti one.

The ones people are riding don’t weigh all that much, but mainly because they don’t have big fat tyres & inner tubes and they have lighter than standard seatposts, lightweight XC rims and a suzue hub rather than a fat splined hub.

It’s a nice material and all, but I’d guess it’s the same as bikes, where there are ultra-lightweight bikes made out of both steel and CF (and other materials), and you can pretty much make lightweight frames from any material.

Personally ignoring the price I don’t think it’s that sensible a material for muni or muni parts for two reasons, firstly that if it gets scratched it needs fixing up and secondly the failure mode is cracking rather than bending. I’ve had steel parts bend and trust me, I’d much rather my seatpost bent and fell off slowly than suddenly went crack and left me sitting on what’s left.

When you take into account the price, we’re talking about hundreds of pounds to save the difference in weight between not eating a pie (mmm pie) before a ride, or (probably less that) not using a DH innertube in your gazaloddi, or just having a slightly lighter tyre.


Re: Helium in tyre…

(All numbers are approximate)

OK this is not practical at all but since Andrew asked specific

The volume of a Gazz 24 x 3 is 600 cubic inches or 3871 cm3 as
Mikefule correctly pointed out. Suppose you have an absolute pressure
of 4 bar in your tyre (that pressure would normally be called 3 bars
since it is 3 bars above the ambient atmospheric pressure). Then you
have an amount of gas in your tyre equivalent to 15.5 litres of air at
atmospheric pressure.

One mole of gas at standard P and T occupies 22.4 litres. So your Gazz
at 4 bars (absolute) contains 0.69 mole of gas. That amount of air
weighs 10 grams. If it were helium it would weigh 2.8 grams, a
reduction of 7 grams. If it were hydrogen it would weigh 1.4 grams, a
further reduction of 1.4 grams. All of that is ‘not something to write
home about’ as the Dutch say.

Like others have said there is the problem of leakage. Helium probably
leaks the quickest because it is mono-atomic and hence very small.
Hydrogen may diffuse through rubber, I don’t know; it does diffuse
through some metals. (It’s not really a safety hazard as the
concentration of H2 in the air will be below the explosive limit
unless you have a MASSIVE leak.) Filling cranks with gas as Andrew
suggested is usually no option, as most cranks are solid. Filling a
frame with gas requires something to shut it off which will ADD
weight. And if it were closed anyway you could make it vacuum - can’t
get any lighter than that as long as we stay away from antimatter. And
an ‘air’ saddle? Not more than a few grams at most.

Pee before you ride, it sheds much more weight!

Klaas Bil - Newsgroup Addict

"Money isn’t made out of paper, it’s made out of cotton. "

Re: Re: Helium in tyre…

Made a mistake there. That much air weighs some 20 grams so there is 10 grams more to gain. Still no big deal.

Klaas Bil