Does anyone know if this would work or even yield any gains? I'm not too sure about how it would work at 100+mph, but I know some people who've done it to thier bmx bikes to save a bit of weight, and that was at 90-120psi. I'm not sure if it would really be rotating or static weight though... because I guess the helium in the tires would just stay in the same spot as the tire spins around it.

My only concern would be it expanding rapidly as the tires heat up...

 

Well it wont be much of a difference. A skinny would hold about 4 cubic feet of air which has a molecular weight of 28, so at 298*K and 40 psi that would only be 355 g. Helium has a molecular weight of 4, so the same volume would weigh 51 g.
Gas that is touching the tire and wheel will rotate at the same speed as the object it's touching but the speed will reduce is you move to the center of the cross section, the reduction of the speed depend on the viscosity of the gas.

 

Yeah... but it would be cool to brag about

 

You'd be stopping a the helium pump fairly often. He molecules are very small and they sorta sneak thru the rubber. Note how helium balloons don't stay inflated many days. It's rarely because the knot isn't tight.

Your typical Camaro wheel and tire goes about 20,000 grams, so as sssalah said, not much gain.

So why would the He expand rapidly (compared to air) as the tires heat up? Are you concerned about the helium bursting into flame perhaps?

I'm not sure I'd brag much about helium-filled tires to scientific types. Ricers might buy it, however.

Using dry nitrogen in your street car tire IS cool.

 

It might want to float off

 

Great idea... wouldn't happen to want to start a business would you?

Nitrogen... hmm, didn't think of that. What else is lighter than air?

 

Ive heard of many people (espeially Truckers) Using Nitrogen in their tires because the molecules are larger thus the tire stays inflated longer not to mention the pure Nitrogen dosent expand as much as regular air.

I also saw it on TRUCKS (with stacey david) on Powerblock. He recommended it because beadlock tires and big mud boggin tires leak more and he said that filling them with nitrogen keeps them inflated longer.

 

A little confusing, since more than 78% (by volume) of air IS nitrogen. And a quick check of the 'net confirms that both nitrogen and oxygen are composed of two atoms, in an ovoid shape, both with a major diameter of about 3 angstroms.

And, why (other than a minor difference in compressability factor) would nitrogen have a different expansion rate with temperature than air? Is it not subject to the same perfect gas law?

The advantage of nitrogen is that it acts as an inert gas, and does not oxidize the tire carcass. As the air migrates through the tire structure, it breaks down the chemical bonds, weakening the carcass, and allow a more rapid pressure loss as porosity increases. Nitrogen still flows out of the carcass, it just doesn't oxidize the components and increase porosity. Has nothing to do with the diameter of the atom or a difference in expansion rate with temperature.

 

Dry nitrogen is important. Air contains moisture (water) and when the tires heat up in a racing situation, the water boils, and the gas expands more.

It's not about the weight of the gas, flat. Forget that part. Hey, if it were, we'd use hydrogen, right? Lots lighter than helium. Lots.

If you want dry nitrogen, buy or rent a tank of it from your local welding supply company. I don't think the nitrogen molecules are much larger than air molecules. Probably a tad smaller. Most race tires are filled with nitrogen because it's dry. They get used up fast, so oxidization really isn't much of a problem, IMO.

Not sure why Stacy recommended nitrogen. He's one of the better car-guy actors on TV. Maybe more car-guy than actor. Admit it now, you watch Powerblock just to see Danica, right. I do... Spent this afternoon at Watkins Glen watching her play with the boys.

Bonus question for flat:If you are going to fill your tires with pure nitrogen, (or helium or hydrogen, argon, etc.) how do you get all the air out first?

 

Why I'd just start the motor and hook a line from the tire to the intake manifold

If you wanted all the air out you could use a vac pump, however it would probably pull the tire off the bead or damage the tire as it shriveled up like a raisin.

 

Good question....

Do you know the answer yourself?

I would think you would have to install the tire onto the rim in a vacuum environment(we'll do this on the moon ) and fill it with nitrogen there.

Or constantly fill the tire with N2 then deflate... fill with N2, deflate... to minimize the % of oxygen to as low as possible level.

 

Good call! That's the practical approach, and one that works. One fairly high pressure fill and deflate should get rid of a very high percentage of the pesky wet air. That was the answer I was thinking of.

 

HEY! Let's use the OTHER idea(taking ricers to the moon to fill tires with nitrogen) and just... leave them. Maybe we'll get lower insurance rates eventually with those idiots off the road

 

Good call! That's the practical approach, and one that works.

 

We use Nitrogen in tires exclusively in aviation for corrosion control purposes. the other added bonus is that if the tire burst from hot brakes no extra oxygen is added to the fire.

(I've seen alot of brake fires on aircraft)