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Tyre pressure stability (air, nitrogen, temperature etc)
- Thread starter Mr Miserable
- Start date
MrBadger
Badger out
Just curious, does the nitrogen fill include a purge ? I'm talking tyres here rather than dentistry...
This is a document I made years ago, and turned it around, that filling with normal air with all the water in it, is even better then with pure Nitrogen. Try to demith this.
Filling car tires with normal air is better then with Nitrogen.
A. Oxygen, which makes 21% of normal outside air, in volume absorbs more energy to rise a degree in temperature then Nitrogen.
Difference is only 1% , but in selling argument is sometimes mentioned in energy/ mass so Joule/kg.degr. Kelvin and there Nitrogen wins by 13 % . Tires though are filled with a certain volume so that counts .
This selling argument can be de-myth simply by the fact that its untrue.
B. Water in a tire transports the heat more then dry air or Nitrogen-filling ( which is by its production process free of water).
Not for no reason water is used in central heating and cooling system of cars as main substance.
The tire inside will have lower temperature which is better for cooling down the important spots of the tire wich have to keep a low enough temperature to prevent hardening and damage in next bending of those parts.
When incidentally the tire inside gets hotter ( sunshine on tire or severe braking, or high ambient temperature) more water goes over to gas wich highens the pressure inside the tire more then dry gas. Also then more water as gas in tire so even better cooling.
So advantage of water is 2 ways when needed, better cooling and lesser heat production.
Disadvantages of water as oxidation only happen at outside . Tire specialists will confirm that when they remove a tire of the rim , the rim inside the tire is not corroded.
C. When a Truck, transporting flammable substance, is on fire, the little oxygen in a tire will , when exploding ,probably even kill the fire .
In tunnels experiments where done to kill the fire with air current , and it worked, despite the oxygen in it.
D. A normal car tire up to truck tire is not a race-car tire, for which a constant as high as possible contact area, so best grip , is needed to give half a second better round time.
For that reason they are filled with as dry as possible air or Nitrogen.
That this gives low lifetime is not important, and for a normal car tire it is.
Often blowing tires at racing, is seen there as collateral damage, but we don’t want that for normal car tires.
E. A car tire is also not a airplane- tire in which the water can freeze and when landing this can give misbalance , which can lead to tire-failure or accident, when suddenly going from zero to about 200m/h.
The water in a car tire does not freeze that often, and when it does and the car begins do drive , it begins slow and the misbalance is not a big problem . then pretty soon, certainly when on speed the ice is melted to water and problem will be gone.
F. When filled with normal air the user is aware of checking the tires regularly, which takes better care of a saver tire, because regularly filled up to the right pressure and optical checking of the tire .
The illusion that Nitrogen filling makes the tire to loose almost no pressure, which is often exaggerated to 5 times , while in real a poor 2 times and then only in the very beginning, makes the user less caring .
The tire also looses air when hitting pavement so temporary leak between edge of tire and rim, Filling with whatever gas-combination won’t prevent that.
This idea is even stronger when TMPS is used which is often inaccurate , so the user thinks to maintain the right pressure, while really riding with to low pressure for longer time, which can lead to tire damage. Aftermarket sensors for TMPS when screwed on the valve can give leakage trough hole where valve is placed , because of the bending of the valve by centrifugal forces at speed.
G. Filling with normal air is always possible, even with a bicycle- pump, is only to fill up so won’t take that long. When you keep driving with to low pressure , in order to find a place to fill with Nitrogen, you damage your tires. So just fill up with normal outside air, even when the tire is filled with Nitrogen. Then also you don’t need to have the tire refilled with pure Nitrogen by your tire specialist when at home again, not worth the trouble, and normal air is even better then nitrogen because of the water in it.
Filling car tires with normal air is better then with Nitrogen.
A. Oxygen, which makes 21% of normal outside air, in volume absorbs more energy to rise a degree in temperature then Nitrogen.
Difference is only 1% , but in selling argument is sometimes mentioned in energy/ mass so Joule/kg.degr. Kelvin and there Nitrogen wins by 13 % . Tires though are filled with a certain volume so that counts .
This selling argument can be de-myth simply by the fact that its untrue.
B. Water in a tire transports the heat more then dry air or Nitrogen-filling ( which is by its production process free of water).
Not for no reason water is used in central heating and cooling system of cars as main substance.
The tire inside will have lower temperature which is better for cooling down the important spots of the tire wich have to keep a low enough temperature to prevent hardening and damage in next bending of those parts.
When incidentally the tire inside gets hotter ( sunshine on tire or severe braking, or high ambient temperature) more water goes over to gas wich highens the pressure inside the tire more then dry gas. Also then more water as gas in tire so even better cooling.
So advantage of water is 2 ways when needed, better cooling and lesser heat production.
Disadvantages of water as oxidation only happen at outside . Tire specialists will confirm that when they remove a tire of the rim , the rim inside the tire is not corroded.
C. When a Truck, transporting flammable substance, is on fire, the little oxygen in a tire will , when exploding ,probably even kill the fire .
In tunnels experiments where done to kill the fire with air current , and it worked, despite the oxygen in it.
D. A normal car tire up to truck tire is not a race-car tire, for which a constant as high as possible contact area, so best grip , is needed to give half a second better round time.
For that reason they are filled with as dry as possible air or Nitrogen.
That this gives low lifetime is not important, and for a normal car tire it is.
Often blowing tires at racing, is seen there as collateral damage, but we don’t want that for normal car tires.
E. A car tire is also not a airplane- tire in which the water can freeze and when landing this can give misbalance , which can lead to tire-failure or accident, when suddenly going from zero to about 200m/h.
The water in a car tire does not freeze that often, and when it does and the car begins do drive , it begins slow and the misbalance is not a big problem . then pretty soon, certainly when on speed the ice is melted to water and problem will be gone.
F. When filled with normal air the user is aware of checking the tires regularly, which takes better care of a saver tire, because regularly filled up to the right pressure and optical checking of the tire .
The illusion that Nitrogen filling makes the tire to loose almost no pressure, which is often exaggerated to 5 times , while in real a poor 2 times and then only in the very beginning, makes the user less caring .
The tire also looses air when hitting pavement so temporary leak between edge of tire and rim, Filling with whatever gas-combination won’t prevent that.
This idea is even stronger when TMPS is used which is often inaccurate , so the user thinks to maintain the right pressure, while really riding with to low pressure for longer time, which can lead to tire damage. Aftermarket sensors for TMPS when screwed on the valve can give leakage trough hole where valve is placed , because of the bending of the valve by centrifugal forces at speed.
G. Filling with normal air is always possible, even with a bicycle- pump, is only to fill up so won’t take that long. When you keep driving with to low pressure , in order to find a place to fill with Nitrogen, you damage your tires. So just fill up with normal outside air, even when the tire is filled with Nitrogen. Then also you don’t need to have the tire refilled with pure Nitrogen by your tire specialist when at home again, not worth the trouble, and normal air is even better then nitrogen because of the water in it.
BTW The argument is that Nitrogen maintains your car tyre pressure for longer than air.
I'm not interested in why aircaft use nitrogen, I not interested in the use of nitrogen in accumulators and I'm not a formula 1 driver. The idea that TPMS is inaccurate when using nitrogen is completely untrue.
However, the point remains, I am not getting any low tyre pressure warnings on cold mornings and the pressure remains pretty constant.
I willing to listen to arguments but it has to be relevant.
I'm not interested in why aircaft use nitrogen, I not interested in the use of nitrogen in accumulators and I'm not a formula 1 driver. The idea that TPMS is inaccurate when using nitrogen is completely untrue.
However, the point remains, I am not getting any low tyre pressure warnings on cold mornings and the pressure remains pretty constant.
I willing to listen to arguments but it has to be relevant.
I got my car at the beginning of September 2019. I haven't had any low pressure warnings no matter the temperature. I do swap for winter tyres (on the same rims) so this is with 2 different tyre brands and styles. Though not receiving any warnings I've probably checked the pressures manually twice since putting the summers back on ... I adjusted the pressure once because they were a bit high as the temperatures warmed. We are about to go into November and I've not actually checked the pressures since the middle of the summer and they haven't dropped enough to prompt a warning (7C all day today here). I am certainly overdue for a manual check but it's wet and muddy where I park even though it stopped raining today! I'll probably not even bother before having the winters put back on. This is with standard air so I don't know what using nitrogen would have done for me.
I agree N2 and O2 are awfully similar. There may be some diffusion rate differences between O2 and N2 through various rubber polymers. I think the diffusion rate difference would vary between different rubber compounds, and rest assured no one regularly measures and reports the diffusion rates. I doubt the diffusion rate is measurable over the few months between tire rotations for most folks. There may be something to the difference in dryness between purchased nitrogen and compressed ambient air. But I would think any water vapor, with its much lower molecular weight, would diffuse out of the tire faster than nitrogen or oxygen.
But we are not discussing N2 versus O2. We are discussing N2 with a little bit of O2 mixed in, versus pure N2.
I also didn’t receive any low pressure warnings at all through the whole of last winter. Ok it was a fairly mild winter, but there were still some days when it barely got above freezing.
The only time I manually check my tyre pressure is when I’ve had a puncture. I’ve had three so far resulting in three new tyres, two of them within a week. Ouch!
Cnixon
Member
Just to add confusion. Given that the tyre is full of air before it is pressurised all you are doing is compressing the Oxygen present at the start with more Nitrogen. So if you put say 2bar in tyre the Oxygen % will still be about 7%.
Glan gluaisne
Active Member
Earlier in this thread I took the time to see what the difference was between air and nitrogen, in terms of the impact of the very tiny difference in molecular size. It seems that nitrogen may, possibly, leak out of a car tyre about 2.1% more slowly than air. This is so far below the variation from things like temperature changing the pressure (which is the same for nitrogen as for air) as to be way down in the noise.
Cleverer people than me have looked at this many times, and concluded that nitrogen gives absolutely no real-world benefit over filling tyres with dry air. The only thing that may make a very tiny difference seems to be the water vapour content of whatever gas is inside the tyre. Dry air would seem to be very slightly preferable to air at normal humidity levels, for example. Whether it's worth paying extra to have a tyre filled with dry air, or any other gas, is very debatable in the UK climate.
In practice, it's very easy to get dry air from a compressed air supply, just needs a desiccant canister, and, as it happens, I've had one fitted to my compressor for years, as any moisture in the air line tends to mess up paint. My tyres have been topped up once with dry air (only because I only have dry air) as the tyre pressures were low when the car was delivered, and the TPMS gave a warning after the first cold night. I've never had a TPMS warning in the ~10 months since, and the tyre pressures seem to be very stable now. The desiccant canister on my compressor takes the water vapour content down to a dew point equivalent of about -40°C, far more than would ever be needed for British weather conditions, but it might possibly make a difference in some very cold climates.
Cleverer people than me have looked at this many times, and concluded that nitrogen gives absolutely no real-world benefit over filling tyres with dry air. The only thing that may make a very tiny difference seems to be the water vapour content of whatever gas is inside the tyre. Dry air would seem to be very slightly preferable to air at normal humidity levels, for example. Whether it's worth paying extra to have a tyre filled with dry air, or any other gas, is very debatable in the UK climate.
In practice, it's very easy to get dry air from a compressed air supply, just needs a desiccant canister, and, as it happens, I've had one fitted to my compressor for years, as any moisture in the air line tends to mess up paint. My tyres have been topped up once with dry air (only because I only have dry air) as the tyre pressures were low when the car was delivered, and the TPMS gave a warning after the first cold night. I've never had a TPMS warning in the ~10 months since, and the tyre pressures seem to be very stable now. The desiccant canister on my compressor takes the water vapour content down to a dew point equivalent of about -40°C, far more than would ever be needed for British weather conditions, but it might possibly make a difference in some very cold climates.
Jason71
Well-Known Member
Tyre rotation!
As far as most of us on this side of the pond are concerned that's an even bigger scam than Nitrogen.
A few people swap front and back maybe once in the life of a set just to get all four to wear out at the same time but that's about as far as 99.9% of us go.
I've not read from the start so this may have been stated already - the rule of thumb is 10 deg c change in temp is about 1.5psi (0.1 bar).
A hot day is probably 25 deg, a cold day -5, so a 30 degree spread across the year and assuming nothing else the presure will vary by 4.5psi.
Its unlikely you set the pressure on the hottest day - lets say the temp was 10 deg so thats a +/- 2.25 PSI swing from target - over inflated in summer, under in winter. Surprisingly few people reduce tyre pressure in summer, only topping up in winter when the alarm goes off.
I think the Tesla warning goes off at about 3-4 psi below target so unlikely to trigger.
So you can leave the pressure uncorrected. This does not mean that it is wise, however.
My recommendation is to check and correct the tire pressure before each long drive after any significant temperature change. The most rapid temperature change happens in March/April and September/October, so those are good times to check and correct. Then again at the beginning of winter and summer, i.e. December and June.
To check and correct make sure the tires are cold and were not hit by direct sunlight on one side of the car.
My recommendation is to check and correct the tire pressure before each long drive after any significant temperature change. The most rapid temperature change happens in March/April and September/October, so those are good times to check and correct. Then again at the beginning of winter and summer, i.e. December and June.
To check and correct make sure the tires are cold and were not hit by direct sunlight on one side of the car.
It's a sensible idea to post that but I think we are taking it "as read". It has long been advised that people should follow the pattern of checking that you describe. The question is whether the stability of tyre pressure is any different if they were filled with nitrogen rather than air. Unfortunately anyone with nitrogen filled tyres is unlikely to have a supply handy for increasing pressures after letting some out in the summer.
Air consists mainly of nitrogen with a small amount of oxygen. Adding 1 or 2 psi with air would add mostly nitrogen and a truly minute amount of oxygen. The tires are unlikely to be entirely oxygen-free anyway.
(I, for one, have air in my tires.)
