Spring rate: Air Vs. Nitrogen?

[timbo]

I think you wrong Ciro
That's because when you consider vaporization the volume and pressure changes abruptly. So when say liquid oxygen vaporizes at 90.2 it will have the same P*V value per mol as nitrogen at the same temperature if both behave as ideal gas.
It is unlikely that they would behave so, however it is tough to predict the deviations from ideality for a given gas.

2ubrben - do you mean freon? In that case it makes even higher difference, for single additional atom you get an increase of heat capacity by R. But I don't think that there's truly big difference in total heat capacity of the tyre with different gases. If you think about that for a second the more heat could gas store the more stable would be temperatures of the tyre that may give that consistency benefits that you mentioned.

[Ciro Pabón]

I might be wrong, Timbo, you know that (when I make jokes about me not making mistakes is because I expect somebody to correct me). I've been thinking since yesterday that the values I got are too high. But it's not that hard to calculate deviations for a real gas. I used the Wohl model for real gases. http://www.ccl.net/cca/documents/dyoung ... state.html

[Jersey Tom]

I'd take Ben's word on this one.

[timbo]

But it's not that hard to calculate deviations for a real gas.

Yes, I meant "predict" in a sense that knowing formula of a gas (say freon) you would be able to calculate deviation from ideality.
Oh, and BTW can dp/dV ratio be considered spring rate?

[riff_raff]

ubrben may well be correct when he states that F1 teams use dry compressed air in their tires now. I haven't been in an F1 pit area in many years.

But back in the late '80s when I was working for a race team, we used compressed industrial nitrogen in the tires. We also used compressed nitrogen cylinders to power the pneumatic impact guns used for tire changes, since the nitrogen cylinders could provide the high pressures (300 psi) we used to drive the guns, didn't require any electricity to run (like an air compressor), and were very easy to move around the pits.

[ubrben]

ubrben may well be correct when he states that F1 teams use dry compressed air in their tires now. I haven't been in an F1 pit area in many years.

But back in the late '80s when I was working for a race team, we used compressed industrial nitrogen in the tires. We also used compressed nitrogen cylinders to power the pneumatic impact guns used for tire changes, since the nitrogen cylinders could provide the high pressures (300 psi) we used to drive the guns, didn't require any electricity to run (like an air compressor), and were very easy to move around the pits.

No of course - I quite agree. Bottled nitrogen is better than wet air. The only problem I have is people trying to convince themselves that there's any difference between dry air and nitrogen.

I would never criticise anybody for using nitrogen. I would however criticise someone who purged a dry air inflated tyre from their tyre company and filled it with nitrogen.

Ben

[alelanza]

And what about Ciro's question of how you get the regular moisture filled air out of the tyre for you to fill it up with whichever dry gas you choose?

[ISLAMATRON]

And what about Ciro's question of how you get the regular moisture filled air out of the tyre for you to fill it up with whichever dry gas you choose?

same way you make a vacuum in an air conditioner system before you fill it with refrigerant.

[xpensive]

Classic physics was never my favourite, but I think urben makes perfect sense, it's just another case of people following a practice without thinking, what matters is the water content of course. If you happen to exceed vapourizing temp that is, but now I hear people are starting to use N2 on roadcars to avoid oxidation of the inside rubber!

And urben, a piece of advise to you as a newbie, if you hope for an admission from the moderator of being in the wrong, perhaps you should try the state lottery while you're at it?

[ubrben]

And urben, a piece of advise to you as a newbie, if you hope for an admission from the moderator of being in the wrong, perhaps you should try the state lottery while you're at it?

I'm a newbie to the forum but if there's one area I know it's race tyres, I'll disagree based on the facts not hierachy

Have never won on a lottery BTW...

Ben

[xpensive]

You are my kind of guy!

[pitlaneimmigrant]

Bottled Nitrogen is still the norm in F1 pits, and in to clarify an earlier question, the tyres are flushed with a filling rig (pressurise, depressurise, pressurise etc etc) to get as much moisture out as possible.

My understanding is that the magical Ferrari tyre gas (some mix of CO2 and R134a or something weird like that) has no effect on spring rate as the compressibility of gases is fairly uniform. The perceived advantage was in it's specific heat which reduced temperature and pressure change (and subsequently spring rate change) as energy was put into the tyre.

[alelanza]

Bottled Nitrogen is still the norm in F1 pits, and in to clarify an earlier question, the tyres are flushed with a filling rig (pressurise, depressurise, pressurise etc etc) to get as much moisture out as possible.

Now that makes sense, thanks!