Nitrogen in tyres
Discussion
ATG said:
ferrisbueller said:
Mave said:
ferrisbueller said:
is it down to the fact that Nitrogen keeps a more constant pressure with varying temps when compared to humble air?
Why is that? Doesn't Nitrogen follow the same gas laws as air, ie PV=mRT?
Is m not different then? Why don't you dig out your steam tables and let us know - don't know where mine are...
This subject was done (to death) a few weeks back, and I think it's fair to say that the conclusion was that the primary benefit of nitrogen was that it was dry. If your tyres are going to get sufficiently hot that condensation inside the tyres will boil, you might benefit from dry gas. Is that going to be relevant on a road car? Nope. It also appears to be true that nitrogen difuses more slowly through the tyre than oxygen ... but given that my air-filled tyres don't need reinflating at all frequently, I can't see how that is supposed to be important.
to be perfectly clear, it isn't that there is anything special about nitrogen ... it's just that nitrogen happens to be an easy way of getting hold of a very dry gas.
p.s. back of the envelope suggests filling with Helium would shave about 20 grammes off the mass of the car.
Edited by ATG on Tuesday 25th July 13:04
Nearly as much as folding the back seats down then
ATG said:
ferrisbueller said:
Mave said:
ferrisbueller said:
is it down to the fact that Nitrogen keeps a more constant pressure with varying temps when compared to humble air?
Why is that? Doesn't Nitrogen follow the same gas laws as air, ie PV=mRT?
Is m not different then? Why don't you dig out your steam tables and let us know - don't know where mine are...
p.s. back of the envelope suggests filling with Helium would shave about 20 grammes off the mass of the car.
Edited by ATG on Tuesday 25th July 13:04
forgive me, it's been a long time. but is the molecular mass of air not different to that of nitrogen, albeit slightly due to the fact 80% of it is Nitrogen? so m would be different.
Not that that really matters as, as i said in my later post i think the quick calcs, that someone later did, based on the steam tables would yield the answer - proven to be negligible.
does helium not give an effective lift of circa 1 kg/m^3? if so, my fag packet calcs, based on a 205/50 15, and assuming it's basically a hollow thick walled cylinder, would yield a lift of around 220grms!
Again, I'm happy to be corrected. The learning is appreciated.
Given that it makes little or no difference then, why are so many people paying the £1 a tyre to have Nitrogen pumped into them.
ferrisbueller said:
ATG said:
ferrisbueller said:
Mave said:
ferrisbueller said:
is it down to the fact that Nitrogen keeps a more constant pressure with varying temps when compared to humble air?
Why is that? Doesn't Nitrogen follow the same gas laws as air, ie PV=mRT?
Is m not different then? Why don't you dig out your steam tables and let us know - don't know where mine are...
p.s. back of the envelope suggests filling with Helium would shave about 20 grammes off the mass of the car.
Edited by ATG on Tuesday 25th July 13:04
forgive me, it's been a long time. but is the molecular mass of air not different to that of nitrogen, albeit slightly due to the fact 80% of it is Nitrogen? so m would be different.
Not that that really matters as, as i said in my later post i think the quick calcs, that someone later did, based on the steam tables would yield the answer - proven to be negligible.
does helium not give an effective lift of circa 1 kg/m^3? if so, my fag packet calcs, based on a 205/50 15, and assuming it's basically a hollow thick walled cylinder, would yield a lift of around 220grms!
Again, I'm happy to be corrected. The learning is appreciated.
Given that it makes little or no difference then, why are so many people paying the £1 a tyre to have Nitrogen pumped into them.
What do you calculate the volume as then? I get somewhere around 0.005m3, which gives a total saving of ~60g at 32psi, unless I'm missing something (it's a looooong time since I did any buoyancy calcs!)
ferrisbueller said:
ATG said:
No the "m" isn't different. It is just the amount of gas expressed in terms of the number of molecules. It's usually written as an "n" not an "m".
forgive me, it's been a long time. but is the molecular mass of air not different to that of nitrogen, albeit slightly due to the fact 80% of it is Nitrogen? so m would be different.
No, the number of gas molecules/atoms (delete as appropriate) in a given volume at a given temperature/pressure is the same no matter what the molecular/atomic mass.
ferrisbueller said:
Mave said:
ferrisbueller said:
Mave said:
ferrisbueller said:
is it down to the fact that Nitrogen keeps a more constant pressure with varying temps when compared to humble air?
Why is that? Doesn't Nitrogen follow the same gas laws as air, ie PV=mRT?
Is m not different then? Why don't you dig out your steam tables and let us know - don't know where mine are...
Don't know what you mean by "is m not different then". Thinking about it, I guess gamma is different between nitrogen and air, but I would have thought you wouldn't be able to measure the difference in pressure it makes with a tyre gauge
Sorry. I could have worded that better. I meant that in the tables there are tables for various gases and their properties at various temps. I think from those that you'd be able to calculate the relative change you'd see in pressure for the different gases for a given change in temp. I suppose you'd assume V as a constant and no leakage.
The "is m not different" thing is based on the fact that if R and V are constant then a given change in T would cause a resultant change in P that would be related to the differing m's.
Feel free to tell me that's all bollox
Coefficient of expansion?
Ok, I understand that my good ladies 306 has one tyre that weighs a little less and it's pressure won't change as much at speed. (Albeit unlikely to get much above 100mph). Given that my digital pressure gauge from Halford (tested by Ride mag to be one of the best) reads in 0.5psi increments. Am I right in thinking I've been charged for something that's not strictly needed in a 306 unless I were to suddenly find myself bobbing round Bridge at Silverstone when it could make all the difference in gettign passed Mr Button and chums?
Edited by gordski on Wednesday 26th July 07:18
I think I'd prefer to have all the tyre pressures changing by an equal amount at speed, rather than have three that increase and one that doesn't.
But is there really so much liquid moisture rolling round inside everyone's tyres, that it creates a serious increase in pressure as it warms up and evaporates? This nitrogen mullarkey strikes me as an expensive solution that's desperately seeking a problem...
But is there really so much liquid moisture rolling round inside everyone's tyres, that it creates a serious increase in pressure as it warms up and evaporates? This nitrogen mullarkey strikes me as an expensive solution that's desperately seeking a problem...
Mave said:
ferrisbueller said:
ATG said:
ferrisbueller said:
Mave said:
ferrisbueller said:
is it down to the fact that Nitrogen keeps a more constant pressure with varying temps when compared to humble air?
Why is that? Doesn't Nitrogen follow the same gas laws as air, ie PV=mRT?
Is m not different then? Why don't you dig out your steam tables and let us know - don't know where mine are...
p.s. back of the envelope suggests filling with Helium would shave about 20 grammes off the mass of the car.
Edited by ATG on Tuesday 25th July 13:04
forgive me, it's been a long time. but is the molecular mass of air not different to that of nitrogen, albeit slightly due to the fact 80% of it is Nitrogen? so m would be different.
Not that that really matters as, as i said in my later post i think the quick calcs, that someone later did, based on the steam tables would yield the answer - proven to be negligible.
does helium not give an effective lift of circa 1 kg/m^3? if so, my fag packet calcs, based on a 205/50 15, and assuming it's basically a hollow thick walled cylinder, would yield a lift of around 220grms!
Again, I'm happy to be corrected. The learning is appreciated.
Given that it makes little or no difference then, why are so many people paying the £1 a tyre to have Nitrogen pumped into them.
What do you calculate the volume as then? I get somewhere around 0.005m3, which gives a total saving of ~60g at 32psi, unless I'm missing something (it's a looooong time since I did any buoyancy calcs!)
My fag packet weight saving calc was based on my guess at the dimensions of an F1 tyre and the assumption that it runs at twice atmospheric pressure and some kids blog that said air density was 1.25kg/m3.
Tyre width 380mm, external diameter 660mm, and internal diameter 400mm(?) ... that gives a volume in m3 of 380/1000 * pi * ( [660/2000]^2 - [400/2000]^2 ) which is about 0.08m3
Twice atmospheric pressure would mean mass density of 2.5kg/m3 ... so the air or nitrogen in the tyre would have a mass of about 200g ... ah hah, this fag packet disagrees with the last one ... and given you've got 4 tyres, total mass would be about 800g
Helium's density is about 0.1 kg/m3 at STP which for the purposes of this calculation is as good as saying it has no mass. Therefore the car could save 800g by replacing the air or nitrgoen with Helium.
Which is lots more than my last fag pack said ... which probably means I forgot to multiply by the width of the tyre in my first calc (which would have meant it was only 1cm wide).
Saving nearly a kilo would be worthwhile to an F1 team, I'd have thought ... so my conclusion is either they aren't allowed to use Helium, or my guestimation of the tyre size is completely wrong.
ATG, while I see the point in an F1 car, I'm still not convinced on the need for a 306. If your calculations are right, then on a 306 tyre I would save less than 0.5kg, or me taking a bottle of pop in the car plus a mars bar. I'm getting the feelign I was ripped off. £1.15 is £1.15 after all!!!!
gordski said:
ATG, while I see the point in an F1 car, I'm still not convinced on the need for a 306. If your calculations are right, then on a 306 tyre I would save less than 0.5kg, or me taking a bottle of pop in the car plus a mars bar. I'm getting the feelign I was ripped off. £1.15 is £1.15 after all!!!!
I've said consistently that I think nitrogen in tyres for road use is pointless ... in fact I would go so far as to say "it's absolute bollox".ATG said:
gordski said:
ATG, while I see the point in an F1 car, I'm still not convinced on the need for a 306. If your calculations are right, then on a 306 tyre I would save less than 0.5kg, or me taking a bottle of pop in the car plus a mars bar. I'm getting the feelign I was ripped off. £1.15 is £1.15 after all!!!!
I've said consistently that I think nitrogen in tyres for road use is pointless ... in fact I would go so far as to say "it's absolute bollox".Tell the garage that and they'll probably insist it is the latest garbage decision from Brussels: all car tyres need to be inflated with nitrogen.
King Herald said:
ATG said:
gordski said:
ATG, while I see the point in an F1 car, I'm still not convinced on the need for a 306. If your calculations are right, then on a 306 tyre I would save less than 0.5kg, or me taking a bottle of pop in the car plus a mars bar. I'm getting the feelign I was ripped off. £1.15 is £1.15 after all!!!!
I've said consistently that I think nitrogen in tyres for road use is pointless ... in fact I would go so far as to say "it's absolute bollox".Tell the garage that and they'll probably insist it is the latest garbage decision from Brussels: all car tyres need to be inflated with nitrogen.
If Brussels is sticking it's 2 euro cents in then expect questions such as
- is nitrogen really that environmentally friendly?
- Do car wheels really need to be round?
ATG - I agree on the 'bollox front'. If it wasn't for the really big chap that works down there I would go and complain, that and the fact it will cost me more than £1.15 to get there and back.
Edited by gordski on Wednesday 26th July 19:28
i have nitrogen in mine, makes no differnece in road cars. it does hold its pressure but it never leaked when it had air in
i just had some lying around the garage which is why i put it in.
it doesn't pick up mositure like normakl compresed air does, and therfore wont fluctuat in humid conditions as much, but i dont have an accurate enough gauge to be able to tell you precisly what the difference is, my gauge only measures single PSI and for that it would need to measure in 0.0 PSI.
in theory it wont get as high a pressure when being run on a long fast run for soem reason or other, but i never bothered trying that either.
the kit i have is for used for filling fire extinguishers, specifically dry powder ones. if you use normal compressed air, the mositure in air can be soaked into the powder which then goes solid and wont work. although you can use dry air, that means compressed through a filter and moisture removing device to a level thats safe to breath, you have to be careful when filling them as if you do it too fast it attracts cold and freezes which again attracts mositure, nitrogen will do the same but it needs a lot higher flow rate to create that effect.
i just had some lying around the garage which is why i put it in.
it doesn't pick up mositure like normakl compresed air does, and therfore wont fluctuat in humid conditions as much, but i dont have an accurate enough gauge to be able to tell you precisly what the difference is, my gauge only measures single PSI and for that it would need to measure in 0.0 PSI.
in theory it wont get as high a pressure when being run on a long fast run for soem reason or other, but i never bothered trying that either.
the kit i have is for used for filling fire extinguishers, specifically dry powder ones. if you use normal compressed air, the mositure in air can be soaked into the powder which then goes solid and wont work. although you can use dry air, that means compressed through a filter and moisture removing device to a level thats safe to breath, you have to be careful when filling them as if you do it too fast it attracts cold and freezes which again attracts mositure, nitrogen will do the same but it needs a lot higher flow rate to create that effect.
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