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[STMO123]

Took a tyre to kwik fit today for a puncture repair. Total cost £22.50 which included £1.50 for nitrogen inflation. Why?

[tigers_gonads]

Nitrogen is a inert gas.
It expands very little when it gets hot so your tyres stay the same presure 

[martin42]

Just need to make sure they do use it as I've seen them use normal air and charged for nitrogen 

[Abiton]

So they can charge more. 

Nitrogen expands just as much as air with heating, air is 80% nitrogen after all...

[Kevin Wood]

So they can charge more. 

Nitrogen expands just as much as air with heating, air is 80% nitrogen after all...

Indeed. It's used in motorsport and aviation because it doesn't contain moisture, which really does expand once it gets hot, and causes more issues if it gets really cold. I doubt it will give much benefit on a road car, though.

Also - ask yourself this. What is in the tyre before they inflate it? That's right. Most of the volume is air before they add nitrogen. The tyre would need evacuating or purging of air if you were to fill it with 100% nitrogen.

[cem_devecioglu]

So they can charge more. 

Nitrogen expands just as much as air with heating, air is 80% nitrogen after all...

Indeed. It's used in motorsport and aviation because it doesn't contain moisture, which really does expand once it gets hot, and causes more issues if it gets really cold. I doubt it will give much benefit on a road car, though.

Also - ask yourself this. What is in the tyre before they inflate it? That's right. Most of the volume is air before they add nitrogen. The tyre would need evacuating or purging of air if you were to fill it with 100% nitrogen.

yep..all gases expand by heat and if it cant expand pressure increases PV=nrT

[smithpa7]

So they can charge more. 

Nitrogen expands just as much as air with heating, air is 80% nitrogen after all...

Indeed. It's used in motorsport and aviation because it doesn't contain moisture, which really does expand once it gets hot, and causes more issues if it gets really cold. I doubt it will give much benefit on a road car, though.

Also - ask yourself this. What is in the tyre before they inflate it? That's right. Most of the volume is air before they add nitrogen. The tyre would need evacuating or purging of air if you were to fill it with 100% nitrogen.

yep..all gases expand by heat and if it cant expand pressure increases PV=nrT

Simple really

[hotel21]

I thought it was to do with molecule size in that nitrogen molecules were 'larger' than standard air thus did not leak through the gaps in the rubber/tyre molecules......

[CaptainZok]

Dunno really B but when you think about it if that were true oxygen leaks out leaving 80% nitrogen and you top it up with air, after a couple of refills it's going to be pretty close to pure nitrogen isn't it?

[hotel21]

Yup, that was also my thinking John when I first read about it yonks ago but it's used in aircraft landing gear so there must be something in it....

[STMO123]

Right. Thanks for explaining that. So there's no danger of my tyres exploding when I drive to asda and take my doggie out. I mean, I sometimes go as fast as 38mph.

[cem_devecioglu]

from
http://www.airliners.net/aviation-forums/tech_ops/read.main/70358/
 
"Aircraft tires are filled with nitrogen because it's a inert gas and therefore doesn't corrode the wheel as opposed to regular compressed air wich contains oxygen, highly corrosive. "

and they say
 
"The main reason for use in aircraft tires as noted in a few instances above is that nitrogen does not react readily with the rubber compounds or metals used in tires and will not support combustion in case of a tire fire.

Nitrogen is also used as a pre-charge for various hydraulic systems in aircraft including the main acumulator and propellors.

Many maintenance procedures include instructions to inject dry nitrogen in various plumbing systems (pitot/static etc) to clean them.

Oxygen in any somewhat pure state on the other hand is very much feared in aircraft maintenance unless you are actually filling the oxygen tanks.

If you expose any type of oil or grease to pure oxygen, it will spontaneously combust (burst into flames) because the reaction with the oxygen is so violent it releases great amounts of heat.

So when oxygen is in use or if you're filling oxygen tanks, don't hang around with your oily coveralls."

[Entwood]

100% Nitrogen is used in aircraft tyres for several reasons :

No moisture: (1) moisture freezes at altitude at the lowest point of the wheel, and would cause massive out-of-balance if solid on touchdown.... if liquid it resists the start of rotation .. (2) It also causes corrosion.

Molecule size : Nitrogen molecules are large in comparison to oxygen and water molecules and so "seep" less thus maintaining a more stable pressure

Temperature change : the different compositions of normal air react to temperature change in different ways, thus a variable "mix" will give a variable response ... 100% nitrogen will be far more stable

An aircraft tyre is subject to tremendous temperature change ... at the end of the take off roll it is extremely hot having had to support the whole weight of the aircraft throughout its acceleration. At cruise it is extremely cold ... around -44 C .. at the end of the landing roll it is once again very hot, both from the weight and the action of the brakes. It also has to withstand almost instant acceleration from stationary to the rotations of 180mph (ish) on touchdown .....so stability is extremely important.

IMHO very few of those facts cross over to "normal" cars, although they may affect F1 cars somewhat more !!

So, again IMHO, a waste of time ... especially if, like me, your tyre pressures change frequently due to load ..

[Richie London]

Right. Thanks for explaining that. So there's no danger of my tyres exploding when I drive to asda and take my doggie out. I mean, I sometimes go as fast as 38mph.

you not got your mobility skooter yet Steve

[STMO123]

Right. Thanks for explaining that. So there's no danger of my tyres exploding when I drive to asda and take my doggie out. I mean, I sometimes go as fast as 38mph.

you not got your mobility skooter yet Steve

I go dirt-tracking with that at the weekend