I think air is permeable to any fabric and pure nitrogen presumably is not, so tyres hold their pressures longer. Don't know all the new cars I have bought come nitrogen filled but they certainly do not need re pressurizing for 18 months or even longer, of course this may just be down to everything being shiny and new.

 

Years ago, service stations used to have a big pressure gauge mounted permanently so less likely to cause inaccuracies due to getting knocked about like the ones attached to the filling hose, have never used service station ones but pump my own with a Argos mini compressor whose gauge reads the same as my 40 year old pop up type (Dunlop) pressure gauge so it must be accurate!!.

Edited 12 March, 20224 yr by Johngerard

1 hour ago, Johngerard said:

I think air is permeable to any fabric and pure nitrogen presumably is not

To repeat, air is 80% nitrogen.

And its 20% oxygen which is where the permeability comes in.

IIRC which is always doubtful, this nitrogen in tyres is from big planes that go up where it's really cold, so possibly in other places where it's really cold it might have some advantage when it's really cold in these really cold places but I'm not sure this includes the UK.

 

Edited 13 March, 20224 yr by nta16

The reason for using nitrogen is that the pressure doesn't change with a change in temperature. 

 

From the "Get Nitrogen Institute" 

Nitrogen provides better maintenance of tire pressure. Because of its larger molecular size, nitrogen migrates through a tire three to four times slower than oxygen. A tire filled with �plain old air� will lose 1.5 PSI in less than a month; with nitrogen, this could take three months or longer.

It’s probable that none of our home gauges are “accurate”. Not mission critical.

 

Its more important to use the same gauge all the time.

 

Like many above, I use a dial gauge at home that is (a) easy to use and (b) consistent in it’s readings.

 

ps - nitrogen in normal car tyres is absolute ******

23 minutes ago, Johngerard said:

From the "Get Nitrogen Institute" 

Nitrogen provides better maintenance of tire pressure. Because of its larger molecular size, nitrogen migrates through a tire three to four times slower than oxygen. A tire filled with �plain old air� will lose 1.5 PSI in less than a month; with nitrogen, this could take three months or longer.

Good point for older tyres. 

From my own experience, newer tyres will last much longer before the tyre pressure drops.

Perhaps that's down to new wheels and better manufacturing processes. 

If consistent pressure is important,  say for track days, then nitrogen is the way to go.

 

12 hours ago, Johngerard said:

From the "Get Nitrogen Institute" 

A tire filled with �plain old air� will lose 1.5 PSI in less than a month; with nitrogen, this could take three months or longer.

If that 'losing 1.5PSI in less than a month' were true we would all be needing to pump up our car tyres on a monthly basis (at least), I check my tyre pressures every week and they have not changed in the last 6 months despite being filled with 'normal' air.

 

My understanding is that the benefit of filling with Nitrogen is that because the process of separating Nitrogen from air involves cooling the Nitrogen obtained is dehumidified and it is this lack of water vapour that reduces the (relatively small but important in motorsport) pressure increases that occur when tyres heat up.

Edited 13 March, 20224 yr by PetrolDave

Would have to agree with that, I can go for months, 5/6, between top ups, present car, a polo, pressures fell ~ 0.15/0.2 bar before I topped up after exactly 3 years., don't know what the ambient temperature was on charging, new, but it was ~ 5C when I topped up, so if one assumes air as a perfect gas and the charging temperature was 15C and the pressure at 2.0 bar then without any leakage whatsoever the pressure at 5C will be (3*278/288)-1, almost 1.9bar, so my pressures probably only fell by 0.1bar or 1.5 psi in 3 years??, not a lot.

Edited 13 March, 20224 yr by Johngerard

I don't know if the quoted article is about car tyres, and I don't know about motorsport but just for once my memory was right about planes.  

 

My wife's Fabia tyres seem to loose a bit of pressure over time but I think that is more to do with all the large holes in the roads around here.

 

Mexicana de Aviación Flight 940(Wiki) - https://en.wikipedia.org/wiki/Mexicana_de_Aviación_Flight_940