the world's craziest idea

what would happen if you filled a unicycle with helium like the tire and frame I have a friend that was looking into buying a bike that was filled with helium and was really lite but does the helium realy make it lighter?? or is it just the carbon frame ? this bike is lighter that light and I like the concept like what if you could make a unicycle that is extremely lite would this really work???

This is really my friend asking but still seams like a good idea.
try this link
hope I don’t sound crazies:o

What are you filling with helium?

The frame? If it’s gas-tight anyway, you’d better suck it vacuum.

The tyre? Would make a unicycle one or a few grams lighter (compared to air-fill) depending on the tyre size. However, regular tyres don’t hold helium for a long time.

Conclusion: impractical idea.


Even if you could spend all that extra cash to seal and use parts to hold the helium, it would not be worth the weight reduction to fill it with helium. It would be as rediculus as filling it with… well, puppies.

I’ve heard of this idea before, I think it was in BMX, but i don’t remember any of the details, as I was in like 4th grade and thought that all the pros used it:p I don’t remember if someone actually tried this, or if it was like this, just a theory :thinking:

Helium is lighter than air because it is less dense. Ergo, to fill a tire properly with helium, you would need more helium than you would need normal air in order to get enough pressure in the tire. In the end, you wouldn’t really lose any weight at all.

nah, it’s still less dense under the pressure of the atmosphere, under the pressure of a balloon, etc.
Why not tire pressure? Though you would probably only save a few grams…


It would certainly dent/bend more easily.
But why is that an issue on a road bike?
It’s not like this is being considered for a trials…and even then you could find a good compromise. It’s not like frames bend inwards before they simply break at the weld.

Air weighs about 0.075 lbs per cubic foot at standard atmospheric pressure. If you have some huge trials frame made of 1" tubing, we can estimate the volume to be somewhere around 30 cubic inches (way bigger than it really is). If you pull a vacuum in said frame you’ll be able to save a whopping 0.001 lbs, or about half a gram!

:stuck_out_tongue: lol, it wouldn’t make your unicycle a lot lighter, and I think it’s expensif to fill your tire,… with helium :smiley:
But you can try it :smiley:

yup. but you have to consider the seatpost, which isn’t practical to have a vacuum in at all, so with 22" of 1" tubing (the sides on a trials frame) I would estimate the volume at 69.1150384 cubic inches, actually.
I dunno where you got 30, so double your calculations
double again for a 36er
and again for the Coker V2
nothing for the nimbus(no air)

even if the uni is lighter, it still has the same mass. it would still be just as hard to move around.

air has mass :roll_eyes:
more so then helium and umm…a very large number of times that of a vacuum.(you’ll never get a perfect vacuum, sorry.)

I gave it 40" of 1" tubing (includes the seatpost)

40*(pi*0.5^2) = 31.4 cubic inches.

sorry, I squared the diameter:o
my bad.
You’re still off though, in the same direction I was.
How do you square a half again?:stuck_out_tongue:
(ok, the seatpost COULD potentially be two feet long…but no vacuum there by any reckoning of mine)

Wow, a lot of bad physics in this thread.

How high do you think atmospheric pressure is? Barometic pressure at sea level is 15 psi. Someone can calculate the yield strength of steel or aluminum, but I assure you that it’s well above 15 psi. The strength of your frame is based on its own structural integrity, not on the air inside it holding it together. Air is highly compressible in any case.

As noted, the unicycle would have less mass, for essentially the same reason that a balloon filled with air has less mass than a balloon filled with water.

Ideal gas law: PV=NRT. Pressure in an ideal gas is a function of the number of atoms of gas, along with volume and temperature. The molecular weight of the atoms is not important; that’s why helium balloons float. (NB: The composition of the gas can make a difference, because real gases do not behave ideally, but for most purposes the ideal gas law is a good approximation.)

All that being said, it is correct that the real effect of filling any part of your unicycle with helium is far too small to be worth doing.

Don’t underestimate the power of 15 pounds added onto normal stress on a frame…but it still isn’t a major problem.

its 15lbs in every direction at all times… not just 15lbs resting on top of it.

That’s still trivial in this context. Think about the force of a 200-pound person-plus-pack landing a 2’ drop; I’m not going to bother calculating it, but it’s probably two orders of magnitude higher than 30 psi. And still our tubes don’t fail in the center; they fail at the weld, which is not where an internal vacuum would apply most of its force.

Why not fill the tire with hydrogen? It weighs half as much as helium. But still, losing even a pound or two, or wearing lighter clothing, or scraping the paint off your uni, would probably have a bigger affect.

Way to re-word the first thing I said on that so it sounds smart :roll_eyes:
15psi could push a near-bend past the limit.
This is highly unlikely(say you run over your uni with a car and the frame is laying on a rail in just the wrong spot), but as air is so light in any case, why are we still discussing this?