F1technical.net

Hi all

For a while, I have been trying to think of reasons as to why nitrogen is mixed with oxygen in F1 tyres. I was of the opinion that nitrogen is denser than oxygen however, recently,I figured out that the it's not so.

What are the advantages of nitrogen over oxygen?

http://lmgtfy.com/?q=nitrogen+race+tires

Nitrogen is just one option. Can use dry air, can use other gas mixtures for various reasons...

Nitrogen doesn't change psi so much.

strad wrote:Nitrogen doesn't change psi so much.

I doubt it. The Van der Waals constants for N2 and O2 are almost identical so the air (in general N2 and O2 mixture) and pure N2 would change pressures identically with the temperature.

http://chemed.chem.purdue.edu/genchem/t ... iation.php

I rather think that the cause is the availability of the compressed nitrogen which may be used as the source of dry gas to pump the tyres if the moisture is the factor here.

I think you are right with your assessment piast9 - IMHO
The critical factor is the moisture content of the gas used, as far as the pressure increase due to temperature goes.

The underlying fact is, that compressed N2 as a "technical gas" is normally "drier" the compressed air.
But if you could have both with the same moisture content, the result would be very similar.

Another factor is related to safety, the absence of oxygene in pure N2 has a benifical effect when we consider the possibilities of an fire, due to high temperatures.
It´s not an issue in racing tires, but a consideration in truck and bus tires.

N2 offers perhaps adventages, when it comes to chemical reactions with the rubber molecules inside the tire, as there will be no oxidation, due to the absence of O2, but this is something, JT or Ben maybe can talk about in greater detail, as I lack the indeep knowledge in this respect.

Just my 2cents - happy to be proven wrong by the tire experts

Thought earlier about advantages in termo properties of N, now see it's not the case.(heard/don't remember source) N has 4 times bigger molecule, than O. Rubber is porous. That can be one of reasons to use N, can it be reasonable?

It's only used because its dry.

Arunas wrote:Thought earlier about advantages in termo properties of N, now see it's not the case.(heard/don't remember source) N has 4 times bigger molecule, than O.

The difference in sizes is 30% however the diffusion coefficients in certain rubber compounds may differ more. But whether this is the reason for using the nitrogen or not - I don't know.

From a chemist: there is no real way of measuring the size of a gas molecule, because molecules are not really made of billard balls. Different methods and different theoretical concepts will result in different sizes for the same molecule, but at all practical effects, for a gas inside a tyre, O2 and N2 are almost identical. O2 is an oxidant though and N2 is more chemically inert.
The key is to avoid having H2O in the tires, which under certain circumstances might even condense, with the concomitant large change in volume and tire pressure.

It was discussed here before:
viewtopic.php?f=6&t=6407&hilit=water+in+tires&start=15

I wonder if you could use helium in the tires so as to make the tires lighter possibly

As JT and 47heavy noted, industrial N2 is used for inflating F1 tires because it is inert and free of water. Since F1 tires can operate at temperatures above the boiling point of water, if there was any water present in the tire's gas volume it would turn to steam, significantly changing the inflation pressure. N2 is also cheap (since the earth's atmosphere is composed mostly of nitrogen gas), and it is handy to have in the pits because the pneumatic impact guns used for wheel changes use high pressure nitrogen gas from cylinders.

http://www.paolipitstop.com/eng/pdf/brochure2010.pdf

The critical factor is the moisture content of the gas used

That was the point...Nitrogen doesn't hold as much moisture

well air has quite a bit N² content so the difference is not that big in real world.

The issue with water content is a LOT more than what you fill into the tyre though

Fitting stone cold tyres in a warm tent or to a warm wheel may lead to condensation on the inside of the tyres...as might a not too well maintained compressor ..I was always amazed in the paddock that nobody seemed to think about that.
And for whatever reason the tyre mounting compound contains water as well so a tyre mounting guy could put in some pressure rise surprises just by using a big blob of that stuff trapped into maybe only one of your new tyres....

I was always very very pedantic or may I say neurotic about tyres wheels etc very closely monitoring pressure rise and drop with temps...eveen before the tyre ever was offered to the car..
To have no oxixene in the wheel should be a good one for the tyre to reduce oxidising..

How much oxidizing is an issue?

there was some story going around that ferrari found out with the special gas they used some years ago found the tyres degrade much less and it was counted towards the gas being inert towards the tyre ...
maybe JT is prepared to comment on this.considering his stance towards nitrogen it may be rubbished in one sentence..

http://www.purigen98.com/ScienceHome.html

the ferrari tyre gas was a mixture 50%Co² and 50% R404A :
A team headed by Andrea Seghezzi of Monza, Italy, in association with Gruppo Sapio developed the gas and subjected it to extensive track testing.

It was discovered that the HFCs were able to effectively conduct the heat generated during the rotation of the tyre to the wheel rim at a more or less constant pressure. The wheel rim then acts as a radiator, exchanging the heat with the outside air, maintaining a lower internal temperature and preventing it from overheating. This is particularly effective on aluminium or magnesium wheels.

Racing rubber inflated with air also suffers from the effects of some internal chemical interactions, which damage the structure of the tyre, and can result in a sudden drop in performance. Due to the high capacity for heat transfer, tyres inflated with the new gas mixture achieve excellent longevity, since the temperature of the tyre is kept low and the pressure is constant.

After extensive tyre testing the best blend of HFCs was found to be 52 per cent Tetrafluoroethane, 44 per cent Pentafluoroethane and four per cent Trifluoroethane. This mixture, known as HFC R404 A, was found to be most effective in a racing tyre when it was inflated with a blend of 50 per cent HFC R404 A and 50 per cent CO2.