Tyre pressure stability (air, nitrogen, temperature etc)

[GeorgeSymonds]

I think the current regulations which warn you of low pressure have lured people into thinking tyre pressures are correct unless they get a warning. I think the systems are really just there to alert of punctures rather than under inflated pressures, and I don't know of any system that alerts of over inflated tyres. Its a regular post on the owners group "whats wrong as all my tyres are showing 37psi" when the correct pressure for their car is 42 or even 45psi.

As for the nitrogen debate, I'm happy with air and check the pressures fairly regularily - it takes seconds in an MS to do so as you set off on a journey. There's far more variability in life with tread wearing down, road surface, temperature etc to worry about pure nitrogen.

 

[Foucault]

Fifth gear tested this a number of years ago and concluded it nitrogen filed tyres weren’t with it. You can watch the video here

 

[jadatis]

In my post #43 , I already wrote that normal air is even better then pure Nitrogen filling, but here some more facts.

First, they dont purge the tire vacuüm before filling with 100% Nitrogen. It would not be good for the tire.

So the only way to come close to 100% N2 is to fill with 100% N2, then let pressure , with tyres off the ground to zero, then fill again, and that in several cycles.
It would take about 3 times as much N2 , so shops will not do that for economic reasons.

But suppose you do it like that, the partial pressure of O2 is higher outside the tire then inside, so on time the O2 will diffuse into the tyre wich compensates a little the N2 diffusing out of the tyre.

O², so I read, difuses 3 times as fast as N², Argon ( Ar) about 2 times as fast, and probably gasshaped water ( H²O) quicker then O². But mayby liquid water much slower.

So certain conditions of humidity and temperature cycles, can make that more water is comming into the tyre, as gas and dont go out as liquid water.
A theory of me, that has to be proven yet.

When you fill the empty tyre, so zero overpressure is 1.013 bar/ 14.7psi absolute pressure, with pure N², with 2 bar, the absolute pressure is 3.013 bar, and so 21%/3= 7% O² is in tire( as someone already gave correctly here) then the partial pressure of O² is the same in and outside the tyre, so yust as much O² is diffusing into the tyre as going out of the tyre, so result is O² amount stays the same,
Then only N2 diffuses out of the tyre.

Even when filled with normal air, a but more N² goes out then O², O² 3 times faster, but there is 4 times as much N² in tyre. The 1% Argon and karbondioxide also partial pressure stays the same.

Enaugh for now, but to answer the disbeleve about O² going into the tyre.
Search for that the law of Dalton, wich states that every gas in a compound reacts for diffusion, as if its the only gas in it.

 

[itzKris]

TL;DL - Nitrogen is all balls, any difference is too negligible to detect! Still, I get my tyres sorted at Costco due to price and quality and they use Nitrogen by default.

 

[Type2]

It was -6.3°C when I left home early this morning and I’ve never had a low pressure warning for my tyres (apart from a puncture) so I reckon normal air is just fine for our climate.

 

[Zakalwe]

My car was showing -9C last week and -6C this morning. No warnings about low pressure in the tyres.

Now, if only they could solve the warnings about blocked side cameras......

 

[pgkevet]

After a string of punctures about a year ago i got into the habit of driving with the tyre pressure display on the binnacle of my S. It's rated at 45psi and I do like to fiddle with an accurate guage so that all 4 tyres show the sme numbers and change at the same time as they warm up in use. (Not so much anal about it as a plaything to get it right using a cheap digital guage that measures tenths).
I repressured them about 6 week ago when we dropped to single figure C's but last week they were all down to 42PSI again and got re-done 'cos we were rattling around 0C ambient here.
It;s easy for me to do since I keep a compressor in the parking barn anyway for all the farm stuff - as much to blow all the crud off things as to keep dealing with tyre issues..

 

[Peteski]

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.

Did you actually pay for this? If so then this is by far the most compelling argument against filling tyres with Nitrogen! It’s a complete waste of money.

 

[itzKris]

Spun off from What did you do to your Tesla Model 3 today?

I went to ATS and had them inflate my tyres with Nitrogen. Pressures much more stable and no losses either.

I get my tyres sorted at Costco, I always assumed the nitrogen nonsense was all balls but delighted that you seem to see real benefit with it.

 

[hgmichna]

Why then at the onset of winter will UK car owners see the little yellow light come on indicating that their tyre pressure is low?
A few miles later it goes out. You will have seen this.

Because you failed to increase tire pressure as temperatures fell.

It goes out because as you drive, the tires warm up, increasing the pressure.

Nitrogen in car tires is nonsense, unless you run a tire workshop.