splash out and fill them with water,

MikeB4:

splash out and fill them with water,

Wiggum:

 

 

 

Well the 20% oxygen/Co2 is not going to leak out by itself, without taking the nitrogen with it.

 

You do realise it was a tongue in cheek joke right?

The tyre shops claim that the nitrogen doesn't leak out, but air will. If you apply that logic, then just fill with air and wait for everything that isn't nitrogen to leak out (because that won't leak). You are left with nitrogen.

RunningMan:

Wiggum:

 

Well the 20% oxygen/Co2 is not going to leak out by itself, without taking the nitrogen with it.

You do realise it was a tongue in cheek joke right?

The tyre shops claim that the nitrogen doesn't leak out, but air will. If you apply that logic, then just fill with air and wait for everything that isn't nitrogen to leak out (because that won't leak). You are left with nitrogen.

Air is (near enough) 80/20 nitrogen/oxygen. Oxygen goes through rubber at about twice the rate of nitrogen, and assuming that permeability is also proportional to partial pressure of each gas. Initially, oxygen will leave the tyre at rate R * 20%, whilst nitrogen will permeate at rate R/2 * 80% (i.e. R * 40%). So, about 2/3 of the air permeating from a tyre initially will be nitrogen, and about 1/3 will be oxygen. If 10% of the air escapes at those rates, the remaining air will be (20-10/3)/90 = 18.5% oxygen, (80-20/3)/90 = 81.5% nitrogen. The proportion of oxygen vs nitrogen in the next 10% to leak will be affected by this changed proportion of oxygen/nitrogen in the air, so proportionately less oxygen will be included in the next 10%. I'll leave the calculation of that as an exercise for students. For extra credit, use integral calculus to calculate accurately the amounts of oxygen/nitrogen loss, and the proportions remaining as the pressure in the type approaches zero.

frankv:

 

Air is (near enough) 80/20 nitrogen/oxygen. Oxygen goes through rubber at about twice the rate of nitrogen, and assuming that permeability is also proportional to partial pressure of each gas. Initially, oxygen will leave the tyre at rate R * 20%, whilst nitrogen will permeate at rate R/2 * 80% (i.e. R * 40%). So, about 2/3 of the air permeating from a tyre initially will be nitrogen, and about 1/3 will be oxygen. If 10% of the air escapes at those rates, the remaining air will be (20-10/3)/90 = 18.5% oxygen, (80-20/3)/90 = 81.5% nitrogen. The proportion of oxygen vs nitrogen in the next 10% to leak will be affected by this changed proportion of oxygen/nitrogen in the air, so proportionately less oxygen will be included in the next 10%. I'll leave the calculation of that as an exercise for students. For extra credit, use integral calculus to calculate accurately the amounts of oxygen/nitrogen loss, and the proportions remaining as the pressure in the type approaches zero.

 

 

 

Excellent analogy. So fill up with air when the tyre goes a bit flat and you end up with a higher percentage of nitrogen anyway. The more cycles of leaking/filling up with air will result in a higher nitrogen percentage every time. So pointless using the nitrogen to begin with.

frankv:

...Oxygen goes through rubber at about twice the rate of nitrogen...

 

Ge0rge:

frankv:

 

...Oxygen goes through rubber at about twice the rate of nitrogen...

 

 

 

 

 

This is the second time I have read that in this thread - does anyone have anything to actually back this up?

Because a molecule of nitrogen gas is 300 trillionths of a metre across, and oxygen is 292. So Nitrogen is only 2.7 per cent bigger than oxygen. That’s not much, so to say that twice as much oxygen escapes through the rubber than nitrogen strikes me as a bit of a stretch...

the question is what is the size "holes" in the rubber.

food for thought: http://www.getnitrogen.org/pdf/graham.pdf

6FIEND:

Important on a racetrack where 1-2psi difference might equate to winning or not...  Almost pointless on the road.

 

nakedmolerat: it actually works if you do it properly.

i have the habit of buying full set of tyres. in the past, my mate runs the the shop. he insisted to have nitrogen in the new set. he did say, the only way to get the benefit of nitrogen, you'll have to pump with nitrogen, deflated it then do it again like half a dozen times. he did that for me for all four. i regularly check the pressure every month. it was close to 9 months before I took it to the tyre shop. by then it drops about 3 psi in all 4 tyres.

i believe it works but it has to be done properly. one of the tyres punctured while I was on a trip. I didn't bother filling in nitrogen and i do feel like it loses air faster than the other 3 (although it could be from the repair).

despite good experience and i think it "works", I will never pay for it mainly because I do prefer filling the tyres regularly and do visual check at the same time looking for nails etc.

heres my go to man regarding the car industry....

https://autoexpert.com.au/buying-a-car/top-10-reasons-why-nitrogen-wont-help-your-tyres

Nakedmolerat sounds exactly like Jimi James . 

Jase2985:

 

the question is what is the size "holes" in the rubber.

 

food for thought: http://www.getnitrogen.org/pdf/graham.pdf

 

Everyone's chasing red herrings with the permeability argument.

More leakage is going to happen at the toe/bead of the tire or around the stem seal than through the tire itself. New tires 'stretch' with age and use, causing more pressure drop at first than leakage.
And unless an explosive wheel fire worries you nitrogen in your tires is a waste of time.

Nitrogen does have its vehicular uses. It's relatively inert, usually dry, and it's density, compressibility, constant expansion rate - and low cost - are the keys to it's use.
My heavier vehicles have nitrogen/oil shocks, and nitrogen filled brake hydraulic accumulators.
Grandad had an Austin Maxi from the late 70's (aka landcrab) with the hydrolastic-hydragas supension (which I marveled over as a kid) A nitrogen accumulator provided the suspension's springing. Was cool.

My truck tires in Canada are filled with Nitrogen. But only because it's free where I get my tires and can't hurt anything.
They use a special 'paste' bead sealant, air is 'purged' from the mounted tire before filling. A green 'nitrogen only' cap screwed on the stem.

Of course none of this produces any real-world gains, and when I top up I use just straight air.
The key is to use dried air – not the moisture laden spray that comes out of most petrol station air fillers.

Most TPMS are waterproof but it's possible to block the port with moisture sludge and be bathed in the hideous glow of the orange exclamation mark on your dashboard.

Sidestep: Most TPMS are waterproof but it's possible to block the port with moisture sludge and be bathed in the hideous glow of the orange exclamation mark on your dashboard.

Bung:

Sidestep: Most TPMS are waterproof but it's possible to block the port with moisture sludge and be bathed in the hideous glow of the orange exclamation mark on your dashboard.

Assuming that your car actually has TPMS modules in the wheel, many manufacturers use the ABS sensors to monitor changes in wheel rotation to do the TPMS function.

Yep, iTPMS gives you even less reason to worry about moisture inside your tires.