Tyre Pressure with Nitrogen.
Turbo Mini Forums

Went to a local tyre depot to get some rubber put on some wheels and they tried to charge me extra for filling them with nitrogen.

So i enquired about said nitrogen and its benfits for my money. I was told F1 bla bla bla etc. Oh wow, so i asked for more. The gas dosen't expand like air giving me more consistent tyre pressures. I couldn't really argue with the last bit. So i asked what they set the tyre pressures to. The guy said "we set them at the manufacturers recommended pressure". I said "but your chart on the wall is for cold air pressures, dosen't this mean my tyre will always be under inflated as the nitrogen will not expand to give me the correct hot running pressure?". He looked confused the poor fella.

I told him to take it out and put air in and knock the few quid of the bill.

The Nitrogen is dry wich is good for limiting corrsion of the wheel, but thats about it for road use, especially as the pressure's you see recommended are cold air temps not nitrogen.

The main reason why Nitrogen is used by F1 etc. is two fold.

1) it is dry so it's density is very constant, even with extremes of temperature. This means more consistency which is ultra improtant when your talking about 1000ths of a second making the difference!

2) Nitrogen is available in nice easy to transport and handle bottles rather than having to carry around compressors etc.

That is how I understand it anyway. Worked with Bridgestone for a while when I was fresh out of Uni but that was just data analysis at base not trackside...

Every day is a school day ...........

How fast and how expensive ...... the same question...

I know all about it. Your right RodgerM

Change of a few lbs can have quite an effect on ride height when you are dealing with big wide slicks. Older flat bottom cars could be really sensitive to this as there were no ride height limits in those pree having half a tree bolted to the underside of the car days !! lol

My point was some that a company sells you this at a cost, they don't know what they are on about and they sell you a tyre that is gonna run under inflated.

Keep ya money in ya pocket and use air at recommeded pressure

Edited by Mirage on 9th Mar, 2007.

Ive used nitrogen once, I carry a bottle in the back of my work van, only used it as my foot pump was broken, lol!
Shane.

Those were the days ........

Looking forward to the "no development era" ... great ..... :(

Every day is a school day ...........

How fast and how expensive ...... the same question...

Service just isn't an option these days.

Every day is a school day ...........

How fast and how expensive ...... the same question...

I dont like the new regs. I think the engine spec fix is crazy, if you have an inherant problem your stuck with it.

Then you get the "in my opinion" the FIA interpreting the rules to suit it's self. Look at the fiasco with the renault mass dampers. They got banned as an adjustable aeroo device as they said it would affect reight height and thus the aero of the car !!!! In that case they should ban springs and dampers.

On the flip side, if you are liked then you can run flat disks on your wheels, despite the rules saying that the wheel must be of homegenous material. It was claimed that the disk was part of the brake duct !!!! I think the rules say that only the wheels & tyres are allowed to be changed in a pit stop.

Gettin a bit of topic ! lol

The bit about not expanding is bull. All gases follow the pv=nrt law.

http://www.jbperf.com/

Yeah, it's the moisture vapour.

And if CO2 hasn't gone mad in the last week or so isn't the atmosphere about 78 Nitrogen anyway !!!!! lol

Jean, your correct with pv=nrt but remember bottled Nitrogen is purified to be nearly perfectly elemental where as air is always going to be a compound, one which is not consistent for altitude, humidity etc.

I didn't say that it doesn't expand, of course it does which is why they still have to put heat into the tyres when running slow etc. I said Nitrogen is more consistent.

Richard was, I think, saying that the co-efficient of thermal expansion will be different and that the manufactures "cold air pressure" is actually relative to the required "warm" running pressure and the relationship would be different between air and pure Nitrogen.

The quote from the spud at the tyre place "The gas dosen't expand like air giving me more consistent tyre pressures" is actually correct when you consider the English colloquisms from Richards part of the world (assuming Stafs). "Like" being used to mean "in the same way as".

Sorry ..... having a 'defend the people day' after having some total fooken idiot try and shoot down my entire team at work .... unfortunately the prat in question is our so called boss...... Of no relevence at all .. sorry.

I'll get my coat.......

Every day is a school day ...........

How fast and how expensive ...... the same question...

Spot on RodgerM. Guess i should have made it a little clearer, but it's friday i'm tired and a few beers allready consumed !! lol

Spud was at my local "Staffs tyre fitters" It's a hole different language up here ! But for all i know spud may have thought it was miracle gas !

Don't forget about the moisture

I was under the impresion that nitrogen is used because of the lack of H2O. Air contains water in a gasseous form, it can form saturated droplets of water within the tyre under certain conditions depending on the Relative Humidity and pressure of the air when pressurising the tyre. This will adversly change the tyre pressures as the tyre heats up and cools down. It is unavoidable when using air. OFN ( Oxygen Free Nitrogen) is Dry and contains no H2O. It is more predictable and as such you can calculate the increase and decrease of tyre pressures more acurately as you have taken the relative humidity element out of the equasion. When there is a saturated fluid present such as H2O, Water, Moisture, condensation, dew, sweat, whatever you wish to call it, you cannot calculate the results The gas laws work on Gasses, not saturated fluids.

The only other reason I see is, air contains helium, the smallest molecule of any sort of volume in air tha can and does leak through the molecular structure of the tyre itself, thereby changing the pressures, but only marginaly, hardly worth bothering about.

I can see it being a benefit on all out race cars where 10th of a second matters, as trye temperatures and pressures can be moitored, and tested with repeatable results to give the optimum figures for the best lap times.

For a road car, i dont see the benefit

Thanks for the clarifications guys. And I didn't want to imply that any of you was talking bullsh1t.

One additional reason I could see not wanting any water in your tires, and it's definitely more valid here in Canada, is that in cold weather if you want to adjust the tire pressure and have to let some air out, you could get a frozen valve which would be very annoying. And you wouldn't even need to have below 0 temperature due to the cooling of expanding air.

Jean

http://www.jbperf.com/

i run helium in my tyres, in the hope that it reduces drag on the drag strip.....

Yep. I think Rodger means air as in a mixture of gases and H2O

And the figures on the charts of cold pressures are based on air with some sort of average humity figure. Not sure what it is though.

Also you tend to get a greater pressure increase on the first heat cycle you put through it as the tyre has some moisture in the inner carcas

Nic i thought you'd started running your car on methane !!! hows it going?

well they are all out for shafting your hard earned money out of you !
you did right

jbelanger too cold for me over there
anything below 5c and iam out of it

mind you worked in -28c in 1 hour bursts for over 5 years

we use nitrogen on aircraft tyres. it is used because of the temperature and expansion rate. if you think when a tyre goes from 0-350mph with 20 tonnes sat on top, its gonna get fecking hot! also it is used because it is inert. ie, when the tyre goes bang, it goes bang, not kaaaaboooooom!

balls to the blower!!!



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