For the same reason that they have wings- you WANT the tires to have substantial weight because they have to keep contact with the track surface. Dropping weight from other areas of the vehicle is fine, but if the tires are too light you start losing traction and grip.
In any case, the weight difference for 10 cubic feet of nitrogen at 17-21 PSI (normal pressure range for an F1 tire during a flying lap) isn’t enough to affect performance, any more than a driver exhaling to drop weight might be.
Actually, chemists no longer refer to the noble gases as inert gases, because they too will react under extreme circumstances.
It is true, that nitrogen compounds are often very reactive, but they should be distinguished from nitrogen gas. In fact, one of the resons so many nitrigen compounds are reactive, is that their major product is nitrogen gas. Nitrogen gas itself is so low in energy that just about any reaction with nitrogen gas as a product is very favorable in energy.
It also follows, that nitrogen gas is so low in energy, that it will rarely react with anything. The noble gases actually refers to the ability of these elements to exist as single atoms without combining with others . I can assure you that a single atom of nitrogen is very very reactive, but nitrogen is diatomic and as such it exists as N2 or nitrogen gas.
I work with extraordinarily reactive compounds in an inert atmosphere box. That atmosphere is nitrogen. Nitrogen gas very rarely reacts with anything, but you are right in that it reacts more often than the most reactive of the noble gases. Nevertheless, you have to understand there is a distinction between compounds that contain nitrogen and nitrogen gas itself.
[ul][li]Less weight is not an issue with racers; if anything, more weight is desirable (to a degree). That’s why race cars are shaped the way they are: the wedge shape presses the car to the ground more as it moves through the air above the track, giving more traction.[/li]
[li]Nitrogen is cheaper than helium. 'Nuff said.[/li]
[li]Gassious helium (He) would leak out more quickly than gassious nitrogen (N[sub]2[/sub]). Helium gas is in units of atoms, nitrogen in atom pairs. The former is smaller, and more likely to leak out through minute pores in the tire rubber. E.g., helium put in non-helium-designed balloons will leak out of them in about a day; air (mostly N[sub]2[/sub]) will stay in them for weeks.[/li][/ul]
Weight is indeed a very important issue, less mass equals to faster accelerations, which make a big difference on a race. Aerodynamic surfaces are what keep an F1 from going ballistic, not the car´s weight.
Back to the topic, for an average car, using nitrogen for the tires won´t yield any value.
But what you said was that nitrogen was very reactive, which it is not. It is reactive, but not very. Some compounds of it are very reactive. Nitrogent itself is comparatively inert.
The op also asked where you would go for a re-fill. I would like to know, because, my local gas station doesn’t have a nitrogen compressor.
Ficer67
Because the teams wouldn’t want the cars floating off into the sky during the race.
I remember reading a book on the history of cycling and it mentioned a cyclist (I can’t remember his name) who was fanatical about weight reduction so he used to do things like fill his tyres with helium and cut off the ends of the laces on his shoes (it was a while ago). But the opinion of the authors was that the few grammes that he saved in weight made no difference however, the psychological boost that it gave him was important.
Well, not quite. Actual movement of gas through a solid is described by permeation, which includes both diffusivity and solubility. Here’s a pdf file explaining permeability in fairly plain language. The page also gives permeability numbers for N[sub]2[/sub] versus O[sub]2[/sub] (among other gases) through different materials. Take a look.
I also borrowed a book from a colleague (Handbook of Gas Diffusion in Solids and Melts by James E. Shelby) that has relative permeability numbers for N[sub]2[/sub] versus O[sub]2[/sub] for rubbers and polymers:
Permeability (10[sup]12[/sup] molecules/(sec*cm*atm)
Material O[sub]2[/sub] N[sub]2[/sub] Factor
Butyl Rubber 0.27 0.066 4.1
Natural Rubber 4.8 1.75 2.7
Neoprene 1.8 0.61 3.0
Viton 0.47 0.17 2.8
The rest of the materials, although having widely different permeabilities, seem to have O[sub]2[/sub] to N[sub]2[/sub] permeability ratios that fall within the same of range. As an interesting side note, permeabilities of natural rubber are 6.3 for helium, ~3.5 for argon, and a whopping 29 for carbon dioxide (!). Not at all what you’d expect just from molecular weight.
Now, I believe that tires are primarily butyl rubber, which exhibits an oxygen permeability that is four times that for nitrogen. Not negligible at all, and perhaps another reason to prefer pure nitrogen (although I imagine the practical effect of the permeation difference isn’t very great).
300psi on carrier otherwise 150psi. I had to change more than a few wheels and brakes on them. I mainly remember being told to stand well away from the blast cone of the wheel when inflating them.
Interesting, Rocketeer, I had never considered that. The only serious tire blowup I ever saw was my skipper taking off on the Connie… with the parking brake set. The catapult did not care a whit that the mainmount tires did not go round and round as they should. It was then we changed his nickname from “mild Bill” to “boom boom.” Fortunately we were near shore and he made a safe landing ar Miramar.
My buddy God of Aircraft Tires says that’s correct: the innermost layer of an aircraft tire is butyl.
I hadn’t realized that the leak rate could be so different between oxygen and nitrogen. Wow.
The innermost layer is the one responsible for gas-tightness. Just reread my last post and realized I should have explained that a bit better.
If these numbers are valid for mixtures of gas (which I’m guessing they are), you’d expect that a tire that has lost pressure through permeation will have lost significantly more (as a percentage or original amounts) oxygen than nitrogen. Even after repressurizing with air, there’s still much less O2 than in atmospheric air.
After a couple iterations, you’ll be approaching pure nitrogen in a tire.
But who cares.
Damnit. As a percentage OF original amounts.