hint... I crunched it down to about 8.1 moles of gas (using 60L per wheel and 80*F). To get grams just multiply each molar weight by 8.1

Hydrogen (H2) = 8 grams
Helium (He) = 32 grams
Nitrogen (N2) = 227 grams
Air = 238 grams
Oxygen (O2) = 260 grams
Nitrous (N2O) = 356 grams
Propane (C3H8) = 380 grams

Yep... Helium would save you ~195 grams per wheel... or about a pound and half per set of 4... of course the primary problem is that Helium only has an atomic radius about 1/2 to 1/3 that of nitrogen gas... it'll leak down 2 to 3 times as fast (and it's damn expensive in comparison).

 

For those that get a kick outta this kinda stuff, here's the ratio of diffusion times for the gasses above compared to air:

Hydrogen (H2) = 3.83 times that of air
Helium (He) = 2.71 times that of air
Nitrogen (N2) = 1.06 times that of air
Air = standard
Oxygen (O2) = 0.96 times that of air
Nitrous (N2O) = 0.82 times that of air
Propane (C3H8) = 0.79 times that of air

Note however that is is assuming the same sized hole for all the gasses... in application the variation from the rate of air diffusion would be much more extreme as additional pores would be available to the smaller molecules, while larger molecules would have even fewer pores (and diffusion rates as a whole).

On a side note... if you were trying to shave some weight over N2 filled tires, Acetylene would be a bad choice. Yeah it's 16 grams less per wheel... but it explodes at pressures above 15 psi.

 

You know there's a problem when you start quoting yourself.

Steve, you obviously have a great deal of extra time on your hands. Might I suggest community service? Or perhaps a new major just for fun? Or how about a lovely trip to the dentist on a midsummer afternoon?



-Mindgame

 

ROFLMAO!

I'm still waiting for an opinion on whether the air (or helium or nitrogen or whatever) sloshes around inside the tire when you launch. I suppose we could put little cilia-like instruments inside the tire carcass (think inner ear canals) and measure it. Maybe Steve would be a good candidate to try this.

 

lol... thanks a lot guys.

I admit it... I miss the sciences from time to time. Biochem major and I'm stuck working at "a small" software company. Make sense? no more than instant information processing.

As for the fluid flow, there are benefits to using lighter gases. Just like fluids, gasses can be measured for viscosity and although I'm sure there are exact measurements for them, most gases are all pretty close to eachother... about a million times less than castor oil.

Viscosity ratios between gasses, I believe it has to do with a cube of the atomic diameter... but its been a while on that one.

Measuring with a rim-mounted sensor might be fine for pressure (aka run-flat tires) but that alone would have be belive the contained air acts somewhat like a spinner (if anyone's seen those damn things on SUVs )... basically friction/sheering to get up to speed, and probably spools down like a flywheel... but with tiny amounts of mass. Centripital force probably plays a little role in this one as well ... and the inner carcas texture would affect the boundry layer thickness in a major way... espeically at the bottom when it deforms/flattens at the contact patch.

calculating volumes, weight, and diffusion rates are easy... flow patterns in such a crazy system would be a nightmare and I'm not too sure any normal probe-type sensor could do it justice.

Maybe the use of Radon gas, an open-end CAT scan, and a portable dyno could help us out. hmmmm.... come to think of it I do know an X-ray technician.

 

the scary part is that we only see what gets posted...........we dont see all the conversations and arguments he has with himself.

 

Hmmm... would you look at that... an online gas viscosity calculator:
http://www.lmnoeng.com/Flow/GasViscosity.htm

Hydrogen (H2) = 0.48 times that of air
Carbon Dioxide (CO2) = 0.81 times that of air
Nitrogen (N2) = 0.95 times that of air
Air = standard
Oxygen (O2) = 1.10 times that of air

 

[On a side note, CO2 is an interesting solution for 4x4 / off-roaders who air-up their monstrous tires after rock-crawling at 5psi... although it's not usually available in a "dry" supply and because of it's low-pressure condensation point tends to be difficult to carry in bulk (N2 cylinders just need to run higher pressures...~4500psi while CO2 is limited to ~1000psi... 4.5 times less gas in the same tank volume )


You made a large error when you figured the capicity of a CO2 tank as 4.5 times less gas than nitrogen in the same tank volume.

When CO2 reaches 1000 psi at roughly 80 degrees it becomes a liquid. The amount of the gas stored now becomes a function of the volume of the tank and the density of the liquid CO2. I would expect to be able to store at least a 100 times the volume of CO2 in a liquid form. Since heat and expansion room are all that is required to change the liquid back to a gas, CO2 would be much more useful for inflating large tires.

I just found this quote, they say 3000% increase from liquid to vapor.

How it works:

The liquid is many, many times denser than vapor. As I recall, the expansion ratio of CO2 is something like 3000%. In other words, a given volume of liquid, for example one cubic inch, will expand into 3,000 cubic inches of gas/vapor. What this means is, there is an enormous amount of potential energy, or “stored” energy in liquid CO2, much more so than in already-vaporized CO2. The more you expand the gas, the less energy it has per given volume. This is why some people refer to “over-expanding” CO2; doing so simply robs it of useful potential energy.

 

whoops... yeah, max pressure only relates gas to gas phase. Liquid (like nitrous, CO2, and propane) would be largely based on liquid density at pressure.

Although "technically" I guess the statement's still correct... you can't possibily store more CO2 gas in the same tank as Helium.... lower condensation pressure demands it... although MOLES of CO2/Helium would be different of course.

 

speed of light is so slow... lets just jump right to the speed of gravity....

 

Actually, I don't know of any drag racers that use anything other than compressed outside air in their tires. I know none of the nitro teams do.

 

Almost all high end endurance racers use "dry nitrogen".

As soon as any one mentions the word "Quantum", I quit reading. Those guy have proved that everything is nothing and nothing is everything and both at the same time!!!

 

Maybe? A final recap.
There are two main reasons for putting dry Nitrogen in a race tire, both have been mentioned.
One, is that N2 expands less then Air at operating temps. This helps reduce over pressurization, which improve consistency, and allow better suspension tuning.
The second, is that it greatly reduces oxidation of the tire. All modern tires have one or several anti-oxidents agents within the tire compound to help with this problem. Under high pressures and temperatures the O2 molecules become very active and oxidation can occure very rapidly.

 

 

LOL!!!

Aside from the fact that now my head hurts and I seem to have odd telepathic powers now...

I asked one of my physics Prof's this and they had a hard time answering:

If you take a volume of gas and compress it, it naturally wants to expand. If you keep compressing it, it REALLY wants to expand. What is the mathematical point at which it gives up and decides to compress itself?

and my personal favorites:

How does Gravity work? Describe gravity without using that term.

What is time? Describe time without using that term.

(The hardcore guys wont be challenged, but I like many others will be picking our brain bits off the monitor)