Nitrogen tyre fill, hidden charges.

w50nky

No doubt you will have to tell your insurance company that you have modified your vehicle from standard too!

lighting_up_the_chalice

Joe_Horner wrote: »

That's fine as a theory except that, by the time you've topped up about 4 times for "oxygen leakage" you're up to something like 99.98% nitrogen in them anyway because each top-up replaces the "lost oxygen" with another 79% or so of nitrogen

Only if, having ripped the pi55 out of you once, you will go back 4 or 5 times?

Joe_Horner

lighting_up_the_chalice wrote: »

Only if, having ripped the pi55 out of you once, you will go back 4 or 5 times?

Sorry, I wasn't quite clear. I meant by using normal air:

If the first fill is 79% nitrogen then, once the "smaller O2 molecules have leaked out" you top up that 21% with more air, which is also 79% nitrogen. So what's in the tyre is now 95.6% nitrogen.

Then the 4.4% O2 allegedly leaks out again, so you top up with (79% nitrogen) air, giving an overall fill of 99.08% nitrogen.

Again, the O2 leaks, so you do a 3rd top up of the lost 0.92% with more air, which leaves the tyre full of 99.8% nitrogen.

By now, when the 0.2% "lost" O2 gets out you're not even going to notice but, if you somehow do, then you add 0.2% air and your tyre now has 99.96% pure nitrogen inside it.

Obviously, I'm ignoring the various trace gasses in that and assuming that you don't top up until all the O2 has escaped each time, neither of which are likely to be valid assumptions. But it still serves to show how utterly pointless nitrogen filling is for normal use :beer:

w50nky

lighting_up_the_chalice wrote: »

Only if, having ripped the pi55 out of you once, you will go back 4 or 5 times?

I think he means that, after filling from normal air line, any losses will be mainly oxygen as the molecules of oxygen are smaller.
Then when you top up from regular airline again and this top up will be approx 79% nitrogen. Each time you top up you are increasing the percentage of nitrogen in the tyre as it will be oxygen which is most likely to leak.

Well, that's how I read it.

Joe beat me to it!

ChumpusRex

Joe_Horner wrote: »

But a fixed volume of gas will raise its pressure on heating by the same amount, regardless of what gas it is, so the pressure change in a nitrogen filled tyre as it heats up will be the same as one filled with (dry) air, or oxygen, or hydrogen.

Correct. The main benefit of nitrogen is that it is dry. Less water vapour in the tyre supposedly results in a more stable pressure. That said, if you actually work this out, the difference is tiny (less than 1 psi difference in the expected temperature range).

The other claimed benefit that nitrogen leaks more slowly, might also be true, but the difference is truly negligible. As it is, a nitrogen fill only increases the nitrogen content in the tyre from 78% to about 93% so there is still plenty of oxygen inside. Moreover, gas diffusion is a two way process: oxygen can diffuse in as well as out. Testing by road safety regulators has suggested that after 3 months, the oxygen content in a nitrogen filled will have risen significantly.

colino

Please don't give it any credence at all. You would have to mount the tyre on the bead then vacuum out the air inside (in such a manner for it to remain seated!) and then re-inflate using pure, dried nitrogen. Apart from potential damage to the carcass of the tyre, this is neatly side-stepped by them simply not doing it.
Monorail anyone?

=rizla=

How much are Kwik Fit et al charging for this.

shaun_from_Africa

w50nky wrote: »

I think he means that, after filling from normal air line, any losses will be mainly oxygen as the molecules of oxygen are smaller

This would only be the case if the only losses were due to the permeability of the tyre itself.
The amount of pressure lost this way in tiny as the majority of air escaping is through the valve not sealing totally and by the tyre bead not forming a 100% airtight seal.
However, I do agree that putting nitrogen in a tyre fitted to a normal road car is pointless.

pinkteapot

ATS did this to my hubby last time we got a puncture. New tyres at a reasonable, fitted price. Then when he got home, I saw £4 on the receipt for the nitrogen-fill that hadn't be requested. He hadn't noticed before he paid. :mad: I would have argued it on principle - they didn't mention it beforehand and didn't ask if we wanted it.

They've lost just as much pressure over time as any other tyre and we've topped up at normal petrol station air pumps, so they're no longer 'pure' nitrogen anyway.

Would remember if we went there again and tell them to fill with normal air!

Richard53

Joe_Horner wrote: »

Sorry, I wasn't quite clear. I meant by using normal air:

If the first fill is 79% nitrogen then, once the "smaller O2 molecules have leaked out" you top up that 21% with more air, which is also 79% nitrogen. So what's in the tyre is now 95.6% nitrogen.

Then the 4.4% O2 allegedly leaks out again, so you top up with (79% nitrogen) air, giving an overall fill of 99.08% nitrogen.

Again, the O2 leaks, so you do a 3rd top up of the lost 0.92% with more air, which leaves the tyre full of 99.8% nitrogen.

By now, when the 0.2% "lost" O2 gets out you're not even going to notice but, if you somehow do, then you add 0.2% air and your tyre now has 99.96% pure nitrogen inside it.

So, by this reasoning, even a tyre filled with ambient air will become 99.99'% nitrogen over time - just a longer time?


Hmmm.