Spring rate: Air Vs. Nitrogen?

[ICA]

I know that many teams (outside of F1) use Nitrogen in tyres opposed to air. I know that this is because nitrogen (should) have no water molecules in it.

But how does nitrogen effect the spring rate of the tyre compared to air?

Regards,

[ISLAMATRON]

I think the spring rate is mainly a function of the sidewall stiffness and the pressure in the tire... the Nitrogen is much more uniform and predictable in its pressure than air because of the above mentioned water molecules.

To answer your question, I dont think it changes the spring rate much, but when it does change it because of the rise in pressure with temperature it is much more predictable.

[ICA]

I remember in the stepney gate saga, when Ferrari's 'special' tyre gas was exploited, they said the biggest advantage was its spring rate over conventional gas'.

Maybe I am wrong, It would not be the first time

[ISLAMATRON]

I remember the big deal being about heat dissipation and coming up to temp faster. Dont remember hearing much about spring rates, but I could be mistaken.

[Miguel]

I'll go a bit off topic here, but since wheels operate at pretty low pressure* and temperature (around 100ºC I suppose), is there that much of a difference between Nitrogen and normal air? After all, normal air is 70% nitrogen. Also, it would be awesome if the engineers here could tell me why there is such a difference.

I could understand a difference in heat dissipation between CO2 and N2, since the molecules have different degrees of freedom and thus different heat capacity, but between N2 and air?

* Due to my work, my scale of pressure is a bit skewed, and "high pressure" for me means around 1 Mbar (yes, megabar)

[RacingManiac]

I think the maindeal for the Nitrogen was that because it is a manufactured gas(with standards and QC processes), the batch control and consistency is a lot better and predictable. Where as regular shop compressed air still depends heavily on the apparatus used and thus adding extra variable that needs to control. Why Nitrogen over argon and other gases initially when they are adopting this for racing, I don't know....

[Flummo]

Water is not the issue, the thing is that nitrogen varies very little in volume when the temperature changes, and inside a tyre that translates to less change in pressure when the temp changes. Oxygen and other things we have in air causes a bigger pressure variation, and since tyre pressure is important for car handling that is bad on a race car. (Yes, there is water in air too, but that would be easier to remove that than to remove EVERYTHING from the nitrogen.)

[Miguel]

Water is not the issue, the thing is that nitrogen varies very little in volume when the temperature changes, and inside a tyre that translates to less change in pressure when the temp changes. Oxygen and other things we have in air causes a bigger pressure variation, and since tyre pressure is important for car handling that is bad on a race car. (Yes, there is water in air too, but that would be easier to remove that than to remove EVERYTHING from the nitrogen.)

Are you trying to tell me that the equation of state of Air (70% nitrogen) deviates considerably from nitrogen? And that they deviate considerably from the Ideal Gas law (pV=nRT)? In a change of about 100ºC and two or so atmospheres? I can believe there's some deviation from the ideal gas law, but I doubt the deviation from, I don't know, van der Waals equation of state, is noticeable.

[ubrben]

Sorry guys - I'm loving the psuedo-science here being used to justify nitrogen in tyres.

Fact is - as Miguel's pointed out, the behaviour of air relative to nitrogen is essentially the same to any degree you can measure.

Any difference in pressure rise will be due to water content alone. Most race tyre manufacturers use a dried air system and it works fine.

I can accept that in a practical sense it's cheaper to use bottled nitrogen rather than buying an air drier, but don't pretend you're getting any effect beyond having less water vapour in your tyre.

As to ICA's comment about the spring rate with the Ferrari tyre gas - sorry simply wrong.

Ben

[Roland Ehnström]

Thanks for clearing that up!

[riff_raff]

The industrial nitrogen gas used to pressurize F1 tires is considered "dry". That is it has almost all moisture removed. Atmospheric air is mostly composed of nitrogen (78%), so chemically there is not much difference between compressed air and compressed nitrogen. The reason compressed air is not used in racing tires is that racing tires operate at temperatures above the boiling point of water. And since compressed air contains water vapor, the water vapor in the tire's air would turn to steam during a race. The water vapor's latent heat phase change would cause a rapid increase in the tire pressure, upsetting the handling of the car. Dry nitrogen has no water vapor present, so a tire inflated with it is much more stable over the tire's operating temperature range.

Regards,
Terry

[ubrben]

The industrial nitrogen gas used to pressurize F1 tires is considered "dry". That is it has almost all moisture removed. Atmospheric air is mostly composed of nitrogen (78%), so chemically there is not much difference between compressed air and compressed nitrogen. The reason compressed air is not used in racing tires is that racing tires operate at temperatures above the boiling point of water. And since compressed air contains water vapor, the water vapor in the tire's air would turn to steam during a race. The water vapor's latent heat phase change would cause a rapid increase in the tire pressure, upsetting the handling of the car. Dry nitrogen has no water vapor present, so a tire inflated with it is much more stable over the tire's operating temperature range.

Regards,
Terry

I'm sorry this is BS. If you pop down and see Michelin or Dunlop at an LMS race they're using dried compressed air not nitrogen. Provided the air drier is of sufficient quality there is no difference between nitrogen or air.

Ideal gas laws still apply and stray moisture can be a factor even if you use nitrogen because the tyre itself can absorb moisture during storage if things aren't controlled well enough.

Once again (with feeling) the gas you use is irrelevant provided the moisture content is low.

Ben

[timbo]

Once again (with feeling) the gas you use is irrelevant provided the moisture content is low.

Ben

The difference between nitrogen and air is small, but I believe that in Stepneygate it was discussed that Ferrari used CO2 and in that case there would be difference as CO2 is triatomic gas and has larger heat capacity that nitrogen.

[Ciro Pabón]

Are you trying to tell me that the equation of state of Air (70% nitrogen) deviates considerably from nitrogen?

Well, I don't know what you call "considerably", but, as usual, you all know my preferred style (long posts with lots of back of the envelope numbers, long live F1Technical!).

Miguel is right about the gas equation. However, remember this, Miguel (btw, with all due respect, are you starting to forget the basics? Too many nuclear equations, I guess...):

The volume of a gas at a constant pressure is directly proportional to the temperature of the gas within its gaseous range.

That's perfectly understandable. If you try to measure the pressure of Nitrogen at, let's say, 50 Kelvin, it's zero, because the thing is solid.

What does that mean? It means that any element that becomes a gas at temperatures below 90.2 Kelvin (the temperature at which oxygen becomes a gas) has a different rate of increase in pressure for an increase in temperature. Let's assume we have a temperature range of 300 to 350 Kelvin inside the tyre, to check the "pressure factor" of both elements.

Yes, yes, I know half of you have thrown your hands in despair after the previous paragraph. However, if I'm not mistaken (and I'm never wrong!).

Oxygen becomes a gas at 90.2K (Kelvin), increasing in volume (or increasing in pressure within a fixed volume for the temperature range mentioned) by a factor of .209, Nitrogen becomes a gas at 77.36K, increasing by a factor of .199.

So, my trusty calculator tells me that there is a difference of 0.01 in 0.209 (5 percent, give or take) of difference in pressure increase when you use nitrogen. As you start with 80% of nitrogen when you use regular air, you "affect" only 20% of 5 percent when you replace air by nitrogen.

In the end, my back of the envelope calculation tells me that you get a 1 percent difference in spring rate for an increase in temperature within the range I mentioned.

Big deal. Considerably? I don't know, but F1 is called the piranha club: any advantage, even if it's a placebo, counts.

However, I have two questions:

First: if the above is true (I repeat, as the mexicans say: I'm never wrong ... and when I'm wrong, I'm enchanting!) why don't they use helium? Helium becomes a gas at 4.22K (the lowest temperature for gas conversion of all elements), which gives me a pressure increasing factor of .158. Please, pass this clue to Williams, not to Ferrari or McLaren...

Second: how do they fill the tyres? Shouldn't the tyres require a complete vacuum before being filled? How do you get rid of the air inside, before filling with nitrogen? Damn, engineering is always full of "contaminants" that scientists don't take in account...

So, my answer is: yes, as spring rate variability goes, nitrogen is superior to oxygen and helium is superior to both. The differences are in the range of a few percent points. I won't go into helium buoyancy and less un-suspended mass, this is for another "stratospheric" thread... and we already had it, including the rotational energy of the lighter gas. We are nuts for racing, don't we?

However, if any entrepreneur is reading this, I have an idea: How about selling Bridgestone Tyres balloons at the entrance of GPs... filled with helium, of course (we should use another name to avoid lawsuits, like "Bridgeclone" or something). That would be funny, and I bet they would sell like hotcakes. Following that, we could sell also Max Mosley Balloons, inflated with hot air.

[ubrben]

Ciro - you might be right I won't claim to have checked everything you've written. But the key point here is that if I have a gas that gives slightly more pressure rise I can just set a cold pressure a touch lower to get the same hot pressure. That's a completely different matter to having a crazy pressure rise due to the tyre having a non-zero moisture content.

Timbo: It wasn't C02 used by Ferrari - it was a refrigerent gas. I've used the same gas in another formula and once you've found the correct cold pressure to get the hot pressure you want it's no different to using dry air - arguably there were some consistency benefits but it was never as clear cut as the media would have you believe following stepneygate.

Ben