16 replies to this topic

[Top Fuel F1]

I know some one who went to the Le Mans (Type) race at Sebring this year. They claim that the teams were inflating the tires with a gas other than ambient atmospheric air. I don't know if this is true; but it did bring another question to mind: What is being used in F1? Even if it is just taken and compressed from the local air, do they dehumidify it or do anything else to it?

[jetsetjim]

Everyone these days uses pure Nitrogen to fill the tyres, as it is much less susceptable to pressure changes over a range of temperatures.. It allows the tyres to stay much more consitent.

[lumepo03]

Well not everyone uses Nitrogen in racing. Many vehicles that run at Le Mans use dry air. Any gas in pure form is stable in its pressure increase.
That is an ideal gas law. Nitrogen is inert so it has the "no fire" risk checked. Filling a tyre with N2 does not give the inflated pressure a pure N2 rating. Instead it only accounts for 2/3 of the total volume. The ambient pressure was already in the tyre so 5 tyre purges would have to be performed to get it to at least 99.5%. There is another gas which is even better then N2 and that is G7 it has a weight benefit and is even less likely to permeate through the tyre.

[Pingu]

What is G7?

[Scoots]

According to Bridgestone the tires are delivered with dry air, and "some, not all teams" replace it with something else.

[AdamLarnachJr]

Is'nt the whole case against air is the moisture content in a compressed line? Hence the wording "dry air"?

[Mark Beckman]

Adam you can buy cheap and quite successful dryers commercially, water contamination for a car spray painter is a serious problem and in line dryers have been available for a long time, but the case against air is heat and the pressure increase that goes with it.

Nitrogen is a great cooling agent and, as has been said already, doesnt have much effect on it under pressure compared to air, thats why it is used also under pressure (100psi to 200 psi is common) in just about any quality racing shock absorber (damper unit).

Many race Teams I have seen use Nitrogen (well a gas in bottles anyway) in their tyres and I have seen a few rally Guys use it too.

[8nebula]

Some tyre shops will even fill your car tyres with nitrogen, however I have never found it makes too much difference.

[lumepo03]

The advantages for using N2 in racing and N2 in street tyres are quite different. The use of any gas in its purest form is to limit the grawth of the tyre. This allows a team to set ride height, adjust dampener rebound, spring settings and aerodynamics without having as large variation once the tyres achieve their operating temperature. By removing moisture the tyre will assume a more desired operating window when it comes to the above. N@ being inert offers the advantage of not being a fire hazard. The same can be applied to a road vehicle but as a tyre approaches operating temperature with N2 the tyre pressure remains closer to a 5% change versus the 25% of air. This can give a road car a smoother ride and less NVH (Noise/Vibration/Harshness) problems. The main reason for use of N2 in a road vehicle is that air permeates through a tyre at the rate of about 1-2 psi per month, which is why after 6 months a tyre that would normally have 32 psi has 23 psi. According to government statistics(pick a country) 80% of the vehicles on that countries roads have at least 1 tyre that is underinflated by more that 30%. This leads to premature replacement of tyres and a waste of petrol as underinflated tyres use more fuel. Imagine riding a bycycle on the pavement and then pedaling on sand. Not only does it use more energy to pedal in the sand it is not very stable when it comes to handling. The rate of permeation with N2 is about 60% less. This is because of the molecular structure of N2. My DATA shows that Michelin tyres have a zero permeation rate. I have several Michelin tyres that were inflated with N2 almost 15 years ago and not 1 psi difference. Temperature changes affect air filled tyres by 1 psi for every 10 f change in temperature. That is that a tyre filled to 30 psi on a 70 F day will be 28 psi on a 50 F day or 41 psi if the tyre temperature was operating at 180 F. This changes the hysterysis of the rubber and thus effects ride quality and performance. Another good reason to use N2 in a street tyre is that air helps promote aging/oxidation. A tyres life expectantcy is 4-5 years. What happens is thta hte air in the tyre chamber causes oxidation to start almost immediately. Add heat and you accelerate oxidation of the rubber and the steel belts. Most tyre dealers call this dry rotting, but say this happens from exposure to sunlight, WRONG. It happens because the steel belts have rusted. The amouint of miles a tyre has driven has no real affect on belt seperation. I have seen failures on tyre, we have inflated with air, after 6 years of just sitting (wrapped in a dark plastic bag stored at room tempertaure).

http://www.nitronics.com/research.htm

N2 tyre use on the road will slowly come into vogue for enviromental reasons as well as economic and safety and performance reasons.

[Pingu]

Originally posted by lumepo03
The advantages for using N2 in racing and N2 in street tyres are quite different. The use of any gas in its purest form is to limit the grawth of the tyre. This allows a team to set ride height, adjust dampener rebound, spring settings and aerodynamics without having as large variation once the tyres achieve their operating temperature. By removing moisture the tyre will assume a more desired operating window when it comes to the above. N@ being inert offers the advantage of not being a fire hazard. The same can be applied to a road vehicle but as a tyre approaches operating temperature with N2 the tyre pressure remains closer to a 5% change versus the 25% of air. This can give a road car a smoother ride and less NVH (Noise/Vibration/Harshness) problems. The main reason for use of N2 in a road vehicle is that air permeates through a tyre at the rate of about 1-2 psi per month, which is why after 6 months a tyre that would normally have 32 psi has 23 psi. According to government statistics(pick a country) 80% of the vehicles on that countries roads have at least 1 tyre that is underinflated by more that 30%. This leads to premature replacement of tyres and a waste of petrol as underinflated tyres use more fuel. Imagine riding a bycycle on the pavement and then pedaling on sand. Not only does it use more energy to pedal in the sand it is not very stable when it comes to handling. The rate of permeation with N2 is about 60% less. This is because of the molecular structure of N2. My DATA shows that Michelin tyres have a zero permeation rate. I have several Michelin tyres that were inflated with N2 almost 15 years ago and not 1 psi difference. Temperature changes affect air filled tyres by 1 psi for every 10 f change in temperature. That is that a tyre filled to 30 psi on a 70 F day will be 28 psi on a 50 F day or 41 psi if the tyre temperature was operating at 180 F. This changes the hysterysis of the rubber and thus effects ride quality and performance. Another good reason to use N2 in a street tyre is that air helps promote aging/oxidation. A tyres life expectantcy is 4-5 years. What happens is thta hte air in the tyre chamber causes oxidation to start almost immediately. Add heat and you accelerate oxidation of the rubber and the steel belts. Most tyre dealers call this dry rotting, but say this happens from exposure to sunlight, WRONG. It happens because the steel belts have rusted. The amouint of miles a tyre has driven has no real affect on belt seperation. I have seen failures on tyre, we have inflated with air, after 6 years of just sitting (wrapped in a dark plastic bag stored at room tempertaure).

http://www.nitronics.com/research.htm

N2 tyre use on the road will slowly come into vogue for enviromental reasons as well as economic and safety and performance reasons.

Twaddle. I repeat, what is G7?

[lumepo03]

I may have gotten the name incorrect on G7 it may actually be called SE7.
Whatever it is called it is a product of Air Products. It is used in the $200 Nike sport shoes. It has also gained popularity in Germany as a tyre inflation gas that is much lighter then air and helps in tyre performance.
I have an technical bulletin from Mario Moniz of Air Products somewhere in my old files, hopefully they are not in my attic in France, as I am in the US at the moment.

[desmo]

Probably SF6, sulfur hexafluoride.

I realize there are flammibility issues, but as an example how much weight, if any, could be saved using elemental H (chosen solely for its low atomic weight) as a tire inflation gas?

[Pingu]

One cubic foot of air weighs 1 1/4 ounces. The molecular weight of Hydrogen is 1/15th that of air. If you guess a tyre having a volume of 2 cubic feet, then, when inflated to one bar (giving an internal pressure of 2 bars absolute) you would have

1.25 / 15 * 2 * 2 = 0.333 ounces (9 grams) which is not much ....

A tyre of the same size pressured on air would weigh 2 1/2 ounces.

[Evo One]

The problem with light gases is that they tend to be able to escape through much smaller holes than heavier gases such as dry air and nitrogen. Hydrogen would be ruled out due to flammability issues and helium would require tyres that had better sealing properties which would probably negate the weight saving.

[lumepo03]

Your calculations on air are theoretical. The real world has moisture content in the air, unless you live in the desert. The inflation of a tyre is also very dependant on the specific baromemtric pressure, how much humidity is in the air. I have seen race tyres with has much as several ounce of water in them. Add the fact that balance weights are added to the tyre and you now have a heavy tyre. Incidently, the Lexus LS 400 had a massive tyre NVH problem (Noise/Vibration/Harshness) that was traced to moisture in the tyre. 1 tyre was found to weigh 1/2 pound more then the others, while trying to cure the problem. This was at the factory not a dealer.

I will try to post a more detailed article sometime in the future or at least pass it on to tech forum editor.

[palmas]

Originally posted by lumepo03
Your calculations on air are theoretical. The real world has moisture content in the air, unless you live in the desert. The inflation of a tyre is also very dependant on the specific baromemtric pressure, how much humidity is in the air. I have seen race tyres with has much as several ounce of water in them. Add the fact that balance weights are added to the tyre and you now have a heavy tyre. Incidently, the Lexus LS 400 had a massive tyre NVH problem (Noise/Vibration/Harshness) that was traced to moisture in the tyre. 1 tyre was found to weigh 1/2 pound more then the others, while trying to cure the problem. This was at the factory not a dealer.

I will try to post a more detailed article sometime in the future or at least pass it on to tech forum editor.

That's why we use air dryers, so the air moisture does not go inside the tyre!

If you have moisture (should I call it a flood) in your tyres, remove it and avoid your traditional tyre inflating place.

[lumepo03]

I conducted a study on inflation stations available at your local petrol/gas station. BFGoodrich/Goodyear/Bridgstone/Michelin trucks at the race circuits were also tested. I also was able to gather information on the "Glitter Domes" tyre retailers. About 1000 compressors were tested and I was only interested in the final product. I was amazed the number of businesses that had state of the art dryers but failed to bleed down their filter tanks. The same goes for the Race tyre mounters. What was truly eye opening were the Petrol/Gas stations. Not only was there water, not moisture but water there were unacceptable amount of oil in one. There was enough to perform a small oil change. Sand debris and some other residue were all to frequent in many of them.

The study used an oxygen analyser to measure the the amount of oxygen in the tyre. Once we broke down the tyre we were able to measure the fluid left in them and to analyse it. Each tyre was balanced and weight before after the the fills. We suffered a 10% loss rate on tyres that were mounted. Most of it at the tyre dealers. The compressor line that the service station used for mechanical work was the best that we tested. About 70% of the compressors that had dryers put out unacceptable amounts of moisture.