N27 - Nitrogen vs Compressed Air in Tyres

[TDIESEL]

If anyone pays to put nitrogen in their tyres for street use, I have a freezer full of ice I can sell to you for your next trip to Antarctica

[wai]

However, when great accuracy is required, changes in pressure are more predictable to racing teams if you use a dry gas or eliminate water vapour.

The problem is that when nitrogen is used in place of air, the water used to seat the tyre is not removed, and neither is the tyre and rim placed in a chamber where it is first dryed and then all the air eliminated and replaced with nitrogen before the bead is seated and the tyre inflated.

So, in the main, it is not going to be that different if at all.

[greymad]

The problem is that when nitrogen is used in place of air, the water used to seat the tyre is not removed, and neither is the tyre and rim placed in a chamber where it is first dryed and then all the air eliminated and replaced with nitrogen before the bead is seated and the tyre inflated.

So, in the main, it is not going to be that different if at all.

In which case might not a silicone spray be used instead?
Anybody here know anything about the process used when aircraft tyres are fitted to rims?
That could possibly be informative...

[Diesel_vert]

The problem is that when nitrogen is used in place of air, the water used to seat the tyre is not removed, and neither is the tyre and rim placed in a chamber where it is first dryed and then all the air eliminated and replaced with nitrogen before the bead is seated and the tyre inflated.

So, in the main, it is not going to be that different if at all.

Racing tyres are designed to operate at relatively high temperatures. For example, the optimum temperature for a Formula 1 dry-weather tyre is around 100°C, so if varying amounts of water vapour were to be present, it would make it very difficult to predict pressures at full racing conditions. In addition, rubber oxidises at an increased rate at these temperatures, which is the other reason why eliminating oxygen helps. Formula 1 tyres have two valves to allow the air inside to be purged.

Further reading:
Tyre use in Formula One - F1technical.net
Under pressure - Bridgestone, tyres, and the importance of air - Formula 1.com

[Diesel_vert]

In which case might not a silicone spray be used instead?
Anybody here know anything about the process used when aircraft tyres are fitted to rims?
That could possibly be informative...

It isn't necessary to fill them in a vacuum.

On braked wheels, aircraft tyres are required to be "inflated with dry nitrogen or other gases shown to be inert such that the gas mixture does not exceed 5 percent oxygen by volume."

An aircraft tyre inflated to say, 200 psi, with commercial grade nitrogen (99.5% purity) at STP conditions, will achieve a nitrogen content of 98.0% - which is probably sufficient enough for the remaining oxygen content not to support any potential combustion in case of a tyre explosion.

So using it in road car tyres is definitely a w**k and waste of money...

I'd say so.
Passenger car tyres simply aren't designed to be subject to such conditions where nitrogen is seen to be significantly beneficial.

Well, maybe except if you own a Bugatti Veyron and regularly do 400 km/h runs.

[greymad]

It isn't necessary to fill them in a vacuum.

On braked wheels, aircraft tyres are required to be "inflated with dry nitrogen or other gases shown to be inert such that the gas mixture does not exceed 5 percent oxygen by volume."

An aircraft tyre inflated to say, 200 psi, with commercial grade nitrogen (99.5% purity) at STP conditions, will achieve a nitrogen content of 98.0% - which is probably sufficient enough for the remaining oxygen content not to support any potential combustion in case of a tyre explosion.



I'd say so.
Passenger car tyres simply aren't designed to be subject to such conditions where nitrogen is seen to be significantly beneficial.

Well, maybe except if you own a Bugatti Veyron and regularly do 400 km/h runs.

Re the Veyron, I'll keep buying the lottery tickets..!
Don't know where the reference to "filling them in a vacuum" comes from - could we still try to find an authority from somewhere who actually has knowledge of the procedure with which aircraft tyres are fitted to the wheels and inflated (with the N2..)?

[Diesel_vert]

Re the Veyron, I'll keep buying the lottery tickets..!
Don't know where the reference to "filling them in a vacuum" comes from - could we still try to find an authority from somewhere who actually has knowledge of the procedure with which aircraft tyres are fitted to the wheels and inflated (with the N2..)?

In any case, it's pointless to inflate a permeable object which is to be used in the open environment for an extended period of time (such as a tyre) using a gas that's 100% pure - nitrogen or otherwise.

As predicted by Dalton's law of partial pressures, oxygen will actually migrate back into the tyre - until the pressure of oxygen equalises to that of the atmosphere (which is 21.2 kPa or 3.1 psi at sea level), given enough time.

In other words, you'll always eventually end up with 21 kPa worth of oxygen in your tyres, regardless of the initial purity level of the inflation gas.

[gldgti]

Got it done for free when I had my R spec tyres put on. I certainly wouldn't pay for it though, it's just a way for tyre fitters to make a few extra bucks in a very competitive market imho....

And the first prize goes to this response!

[Transporter]

could we still try to find an authority from somewhere who actually has knowledge of the procedure with which aircraft tyres are fitted to the wheels and inflated (with the N2..)?

You could ask Gavin he could know more about it View Profile: h100vw - VWWatercooled Australia

[GarryO]

I'd always understood that the reason in motor racing for using N2 rather than air was to minimise pressure rise with increased temperature - as the air, even though being 78% N2, had a greater coefficient of themal expansion. In street use I see it as a load of w**k - something to brag about (like 35 profile tyres in the street, but it's only my opinion .. go ahead & spend the $$ if you want).
What I had NOT thought about was the use of N2 in aircraft where it's bleedingly obvious that if the tyres are subjected to hours of seriously sub zero temperatures, you don't want the pressures to be off (ie below) spec when you touch down. Thanks, Wai...

The reason for using nitrogen in aircraft tyres is not pressure but because of the condensation freezing and the instability that can cause, can you imagine a chunk of ice forming on the inside of the tyre and then being suddenly subjected to the massive acceleration found in typical use in even a small aircraft tyres upon landing.
Dry compressed air will give the same benefit and can be readily sourced from any dive shop that fills SCUBA tanks.

[San Gimignano R]

The reason for using nitrogen in aircraft tyres is not pressure but because of the condensation freezing and the instability that can cause, can you imagine a chunk of ice forming on the inside of the tyre and then being suddenly subjected to the massive acceleration found in typical use in even a small aircraft tyres upon landing.
Dry compressed air will give the same benefit and can be readily sourced from any dive shop that fills SCUBA tanks.

There are more reason that this.

Does not promote corrosion as an inert gas. Will not intensify fires (brake) if tyre deflates or explodes from rejected takeoff and the likes and heat/fire is present.

As a nitrogen molecule is larger than oxygen, thus gases are less likely to slowly leak from solid rubber retaining a longer constant pressure. http://www.getnitrogen.org/pdf/graham.pdf

Less susceptible to temperature AND pressure changes due to a higher absorption coefficients.

A few of many reasons...

San G.
(Airline Pilot)

[greymad]

There are more reason that this.

Does not promote corrosion as an inert gas. Will not intensify fires (brake) if tyre deflates or explodes from rejected takeoff and the likes and heat/fire is present.

As a nitrogen molecule is larger than oxygen, thus gases are less likely to slowly leak from solid rubber retaining a longer constant pressure. http://www.getnitrogen.org/pdf/graham.pdf

Less susceptible to temperature AND pressure changes due to a higher absorption coefficients.

A few of many reasons...

San G.
(Airline Pilot)

Interesting link - good reading: I presume that when you refer to "absorption coefficients" you are talking about "permeation"?
The argument given in the link however, seems to compare/contrast the behaviour of pure O2 with pure N2.
Which would be fair enough, except that, as we know, air is already ~ 80% N2.
Since you're in the industry can you ask around as to what (if anything) is used to provide lubrication to seat the tyres on the rims?
Thanks...

[San Gimignano R]

This is true WRT pure O2.

Permeation is "the flow through of one substance through another".

I will try to find out your answer, however the biggest reason for its use is the inability for Nitrogen to "feed" a fire.

The effect of temperature and pressure mostly affects the contaminants in compressed air, ie moisture as previously stated. Whilst it will fluctuate the Nitrogen will fluctuate much less that that filled with "air".

[greymad]

This is true WRT pure O2.

Permeation is "the flow through of one substance through another".

I will try to find out your answer, however the biggest reason for its use is the inability for Nitrogen to "feed" a fire.

The effect of temperature and pressure mostly affects the contaminants in compressed air, ie moisture as previously stated. Whilst it will fluctuate the Nitrogen will fluctuate much less that that filled with "air".

Yeah, "permeation" is a new word for me ... I'm much more familiar with "permeability" (not to be confused with "porosity").
Look forward to the gen on tyre fitting procedure for aircraft: thanks.

[brad]

Look forward to the gen on tyre fitting procedure for aircraft: thanks.

I worked at QF Engineering for 17 year. Hands-on in the components area & then planning for sheet metal, undercarriage, machine shop, interiors, evacuation systems, prop shop & other stuff, so I was never directly involved in the wheel shop.

From observation:
Widebody rims are in 2 halves with an o-ring seal. The o-ring gets a light coating of oil/lube but everything else is wiped clean with alcohol.
The tire is dropped on the rim-half, o-ring fitted & the other rim-half fitted & bolted/torqued. Tire assembly is placed in a cage, then they simply try & inflate the tire. If it won't seat with normal pressure then i think they used talc to lubricate the bead.

They did have some type of purging process but I never looked very closely (usually walking to the canteen). They used to let them sit for a few days as well & would periodically check the pressure.

Sorry i can't be more helpful but it wasn't my area. Ask me about bench testing an RR RB211 Variable Inlet Guide Vane controller & I can make a bit more sense (not much though).