Tires filled with helium: what?

[Alphamazing]

I'm watching Mythbusters right now, and they're talking about a football filled with helium and the distance it goes. I've also heard some bicycle racers fill their tires with helium. What do y'all think the effect of filling OUR tires up with helium? Any effect?

[brembo]

I know a few guys who put Nitrogen in their tyres, supposedly it's less prone to pressure fluctuations and slow leaks  No idea if it actually works that way, but they get it for free so why not eh.

[ajgs500]

It will be real great when ur tires get hot and the helium causes them to explode....anyone remember the Hindenburg?

[Alphamazing]

It will be real great when ur tires get hot and the helium causes them to explode....anyone remember the Hindenburg?

Umm, that was HYDROGEN, which is extremely flammable. Also, it wasn't caused by pressure.

[Church6360]

double crap, i missed mythbusters. i dunno, less mass inside the tire, less rotational mass? but enough to matter? i donno, call the mythbusters and get hem to ask a moto GP rider (like colin edwards, or rossi) to flog a bike with different gasses in the tires and see if it maes a diference.

[Caffeine]

IMO, it's a waste of time/money to fill them with anything but air.  All that helium or nitrogen would make a difference of what, a gram or two?   Maybe a psychological advantage for racers.

Helium: not flammable
Nitrogen:  Highly explosive.   Which might make a sudden flat tire (and a stray spark from the rim on the track) very interesting!   

[sledge]

Nitrogen is not a flammable gas, are you getting mixed up with Hydrogen? Nitrogen is inert and whats termed a dry gas ie has no disolved water in it unlike air. One of its uses is for inflating aircraft tyres that are subjest to temperatures way below freezing point.

[Wrecent_Wryder]

=78

[sledge]

I dug out some data sheets for industrial gasses and I have just done some rough calculations in my lunch hour in a attempt to see if compressed helium would offer any weight saving advantage over compressed air. I had to estimate the total internal volume of the tyre and wheel and I assumed a tyre pressure of 35psi and didnt account for any change in temperature and its effect on the gas. I wont bore you all with the figures and how I did it but in conclusion the difference in weight is negligable and you would save more weight by having a damn good C*** before you got on the bike!!

[Ed89]

You probably can use the ideal gas law to estimate how much lighter it makes the tire, say for a volume of pi * 17 inch * pi * (3 inch)^2 at 35psi and ambient room temperature.  But if you really want to explore more, you have to think about the rotation of the tire and the moment of inertia of a torus and how it affects acceleration and turning characteristics.

What the hell, let's see what's the difference in weight.

Estimating from that fact that 1 m^3 of air is about 1kg (as comparison, 1 m^3 of water is 1000kg), and the volume of the tire is about 1500 cubic inch, which translates to 0.025 cubic meter, that means there is about 0.025 kg of air in a punctured tire.  Since we ride with tires that are not punctured, say at 35psi, which is 35psi above atmospheric pressure, and 1 atm (atmospheric pressure at sea level) is about 14.6 psi, so 35 psi is about 2.5 atm, but that is guage pressure so we have to add 1 atm to make it 3.5 atm absolute pressure.  Assuming the ideal gas law PV = nRT holds (which should at this pressure and temperature range), it is a simple ratio so a tire at 35psi has about 3.5 * 0.025kg = 0.08kg of air.  Now, air is mostly (78%) nitrogen, which has a molecular weight of 14, and helium has a molecular weight of 4, then the ideal gas law again will tell us that if we use helium instead of air, the helium will weight about 4/14 less, so about 0.025kg.  That's a weight saving of about 0.05kg, or for SI-impaired people (you know who you are ), roughtly 0.1 lb.

[EDIT: foobar in calculation, I can't multiply ]

Not a whole lot.  I am not going to do the moment of inertia jazz.    Probably won't make much of a difference in handling characteristics anyway.


Cheers,
e.

P.S.  Yes, Helium has a very high diffusivity because it is such a small molecule, i.e., it will leak big time.  In fact, you can put helium in a completely sealed (weld it if you want) inch-thick canister, and it will seep through the steel.  I kid you not.  Air will seep through steel (or any other solid, porous or otherwise) as well, just not as fast.

P.P.S.  Helium is super inert.  Hydrogen they use to send the space shuttle into orbit, so not very inert.  Nitrogen molecule is also inert, but some nitrogen compounds are very explosive.  The 'N' in TNT stands for nitrogen.

[annguyen1981]

I know a few guys who put Nitrogen in their tyres, supposedly it's less prone to pressure fluctuations and slow leaks  No idea if it actually works that way, but they get it for free so why not eh.

There is a couple tire shops in my area that are offering Nitrogen for your tires, and they claim the same things...  Slow or no leaks, and less fluctuations due to temp changes.  I've been considering it for my car for about a year now.

[sledge]

I got the figure of 0.02333 (rec) kg. I could easily manage that first thing in the morning after a night out on the beer and a good curry! 

[Jake D]

And just to clarify, gravity is a force, not an acceleration. 

[skrap1r0n]

It will be real great when ur tires get hot and the helium causes them to explode....anyone remember the Hindenburg?

[ukchickenlover]

From a quick search on the web I found this

''Another interesting point is that most of the F1 teams use dry nitrogen gas to inflate their tyres instead of air. This is done for two reasons. Firstly the moisture content of air is variable depending on the local weather conditions and this differs considerably between some of the exotic locations on the GP calendar. By using dry nitrogen gas the tyres will behave in a predictable way wherever they are being used. The second reason is that air is a mixture of nitrogen (78%) and oxygen (21%). Oxygen gas is far more reactive than nitrogen and at the high operating temperatures of F1 tyres (> 100°C) the oxygen reacts with the tyre, reducing the total pressure inside. Using pure nitrogen removes this problem and tyre pressures remain far more consistent.''

[sledge]

There is a garage near me making claims that Nitrogen is a better option in tyres than air. I can believe that in certain applications its can be benificial and offer certain advantages such as aircraft and F1 cars but I cant see what good it will do in a bike tyre other than to reduce the risk of corrosion to the wheel. When the tyre and bike makers start to say put Nitrogen in thats when I will start doing it.


http://www.merityre.co.uk/why_nitrogen.htm

[ajgs500]

Ehhhh helium hydrogen who cares!!!!  Silly boys!!!!  Fire is always cool!!!  FIre!!! Fire!!!!

[RVertigo]

Well, even according to the MythBusters, there was a weight difference when they used Helium to fill the football...  In fact, the helium filled ball was lighter than the empty ball...  But, only by a few grams or something...


It would probably make a weight difference in a tire, but I can't imagine anyone would use it because it leaks so much.

[gsmetal]

Several years ago I read an article from the World Helium Council based in Recatastan, Norway. Several engineers performed month long tests to see if they could increase the mileage of conventional cars and trucks by replacing the air in the vehicles tires with helium thereby making the vehichles lighter.

After a two month span, they were able to log a 34% increase in MPG.

The article was largely unnoticed here in the USA - suppressed by the big oil companies no doubt.

You can see the results of the test via this link:

http://www.am.qub.ac.uk/mecpc/mpegs/multi2_014.mpg

[Caffeine]

Whoops!  Yeah, I typed "nitrogen" instead of "hydrogen".  That's what I get for posting at 5:00 in the morning!