Low pressure tyre warning

[ukslim]

I'd use the air pump in the boot if I was dealing with a puncture. But for a routine inflation, I found its pressure gauge was far too vague, so I used the air pump at a garage. It's only a couple of times a year -- when the weather turns colder. Same for any car.

 

[mg4mc]

I'm going to do the same as I did with my last car ,last winter for £5 got the air changed out for Nitrogen, far less fluctuations in pressure with winter temperatures.

Evidence? Beyond the claims from the nitrogen fillers.

I also interested how they "changed" the air? Did they stuck it all out with a vacuum pump until the tyre was squished against the wheel, then fill it up again? Or just release the pressure and fill with nitirgoen leaving a whole tyre full of air in there? Or...?

I've always been sceptical of nitrogen filling.

My take...

Both nitrogen and oxygen are ideal gases and expand with temperature at the same rate.

See this page where they tested nitrogen, carbon dioxide, and "air". Spoiler: the pressure changes with temperature were all the same for practical purposes!

It is often quoted that oxygen diffuses faster through the tyre rubber than nitrogen. However the only research that I can find behind this claim is an experiment using "thin rubber sheets" i.e. party ballon type rubber. That is very different from a car tyre. And the difference in the diffusion rates was tiny anyway! Not surprising as nitrogen and oxygen molecules are almost the same size - nitrogen a tiny bit smaller despite a longer bonding length due to a tighter electron cloud.

If oxygen did get lost faster, then each time you topped up the pressure with air you would be replacing the lost oxygen with 78% nitrogen. So the percentage of nitrogen would go up each top up.

 

[olliewebb]

See this page where they tested nitrogen, carbon dioxide, and "air". Spoiler: the pressure changes with temperature were all the same for practical purposes!

Yeah it's a con that fast-fit places have gotten in on to extract money. Every time my M140i went in for tyres they'd try it on, my response, "if BMW wanted Nitrogen in the tyres it would be done at the factory".

 

[fnegroni]

Filling with nitrogen does mean several inflation and deflation cycles to remove as much as possible of any other gas molecule.
In particular, it’s not really about nitrogen per se, but to remove water molecules which affect tyre pressures in a much more unpredictable way. For regular car tyres it’s most often overkill and unnecessary, but the benefits of more stable and predictable tyre pressure is not to be ignored. Whether it’s worth the price is down to personal circumstances

 

[Kithmo]

Nitrogen filled tyres are the equivalent to gaseous snake oil.
How to fill your tyres with nitrogen for free:
Fill with air which is 78% nitrogen
Wait until the pressure drops about 22%, when most of the oxygen will have permeated through the tyres (yeah right)
Refill with air this will give you 95% Nitrogen content in the tyres
Wait until the pressure drops by 5%
Refill, this will give you 99% Nitrogen.
Of course this will take a considerable amount of time due to how slow the oxygen and other gases permeate through the tyres, so it might be better to get a new set of wheels and tyres whilst you are doing it.

 

[Buster72]

Atmospheric air is mainly nitrogen anyway.

 

[mg4mc]

Filling with nitrogen does mean several inflation and deflation cycles to remove as much as possible of any other gas molecule.
In particular, it’s not really about nitrogen per se, but to remove water molecules which affect tyre pressures in a much more unpredictable way. For regular car tyres it’s most often overkill and unnecessary, but the benefits of more stable and predictable tyre pressure is not to be ignored. Whether it’s worth the price is down to personal circumstances

Whilst water vapour does not behave as an ideal gas the percentage present in "air" varies from almost zero, to a maximum of around 4% at 100% humidity on a hot day.

The "air" sample in the page I linked would certainly have contained water vapour - it had negligible effect.

Again - do you have any evidence that water vapour causes a significant variation in tyre pressure?

 

[Saintsman]

Mine did it yesterday must be the colder weather. Couldnt see how acknowledge or reset alarm after drive and tyres warned up. After our walk came back drove away and still on till we went over a certain speed.. 20?

You are not able to aknowledge or reset the the alarms.
the alarms will disappear after you have pumped up the tyres and driven for 0.5 miles.
Hope this helps.

 

[fnegroni]

Whilst water vapour does not behave as an ideal gas the percentage present in "air" varies from almost zero, to a maximum of around 4% at 100% humidity on a hot day.

The "air" sample in the page I linked would certainly have contained water vapour - it had negligible effect.

Again - do you have any evidence that water vapour causes a significant variation in tyre pressure?

Define ‘ significant’

Is 0.1 PSI significant? That’s the sort of adjustment GT3 tyres are sensitive to.
If F1 teams do it they must have enough evidence.
I don’t bother myself but I’m not here to argue whether the difference is significant.
I’m just saying if you get it done you might get that benefit. End of.

 

[olliewebb]

End of.

 

[ukslim]

If F1 teams do it they must have enough evidence.

F1 teams are in the realms of "marginal gains". If it means 1 lap more between tyre changes, it might make the difference between winning and losing. And they're in a realm where money is essentially no object. If there were a gas costing £1000 per tyre, and it got them a marginal gain, they'd do it.

 

[mg4mc]

Maybe, but we're talking about MG4 not a F1 car where 0.1 of second matters on a lap.
Show me a car pressure gauge that you can warrant is accurate to 0.1 PSI.

This started with the claim that low pressure issues as winter approaches would be much less of a problem if they were filled with nitrogen. We are talking about ~3 PSI changes here (2.55 -> 2.35 bar). So, let's call 3 PSI "significant".

 

[fnegroni]

Maybe, but we're talking about MG4 not a F1 car where 0.1 of second matters on a lap.
Show me a car pressure gauge that you can warrant is accurate to 0.1 PSI.

This started with the claim that low pressure issues as winter approaches would be much less of a problem if they were filled with nitrogen. We are talking about ~3 PSI changes here (2.55 -> 2.35 bar). So, let's call 3 PSI "significant".

Hey, I said it myself, for road tyres on road cars it’s overkill.
But one was arguing about the process, I explained it takes several inflation and deflation cycles and that at most achieves 94% nitrogen.
The tyre pressures will be more consistent.
Whether that is worth doing it’s not for me to decide.
Just like many things in life, it’s a placebo.
Like helmets for cyclists.

 

[AB71]

Hey, I said it myself, for road tyres on road cars it’s overkill.
But one was arguing about the process, I explained it takes several inflation and deflation cycles and that at most achieves 94% nitrogen.
The tyre pressures will be more consistent.
Whether that is worth doing it’s not for me to decide.
Just like many things in life, it’s a placebo.
Like helmets for cyclists.

Helmets for cyclists a placebo?
Please explain

 

[olliewebb]

Helmets for cyclists a placebo?
Please explain

It's more complicated than this. Worth looking into yourself, but there is some data that shows overall fitness levels and more people cycling increases when helmets aren't a barrier. The risk of not enforcing is off-set by health gains. I've not personally seen any studies that are UK specific though, mostly around the Netherlands and their bike-friendly culture.

It's not an outright placebo (by definition) - but things need to be understood, sweeping or throw-away statements are not useful. I wear one personally for a number of reasons - a lot of them include the type of off-road riding I do.

There is also a reason why Cycle2Work-style schemes include provision for accessories such as helmets.

 

[fnegroni]

Helmets for cyclists a placebo?
Please explain

Oh. There’s plenty of scientific evidence showing helmets have almost no impact on KSI statistics in urban areas. And a massive impact on cycling uptake in urban areas.
Yet cycling helmets can cost well over £100 and there’s no evidence that will convince someone not to wear a helmet if they believe it saved their life, because ‘placebo’

 

[AB71]

It's more complicated than this. Worth looking into yourself, but there is some data that shows overall fitness levels and more people cycling increases when helmets aren't a barrier. The risk of not enforcing is off-set by health gains.

It's not an outright placebo - but things need to be understood, sweeping statements are not useful. I wear one personally for a number of reasons - a lot of them include the type of off-road riding I do.

Ah I see. I had a Mums head on then remembering daughter riding helmet- less straight into a piece of steel and cutting her head open.
You’re talking proper adults biking stuff real avid cyclists so I shall step back into the shadows

 

[fnegroni]

Btw I’m not arguing that under the right circumstances and in particular scenarios they may well save your life.
But so will a full downhill armour
It is not practical though. So there you have it: if you think it will make a significant difference….

 

[AB71]

Btw I’m not arguing that under the right circumstances and in particular scenarios they may well save your life.
But so will a full downhill armour
It is not practical though. So there you have it: if you think it will make a significant difference….

All I remember from that night is if she had of been wearing her helmet/cycling hat like she was told she wouldn’t have been left with the Harry Potter nickname. such is life I guess.

 

[fnegroni]

All I remember from that night is if she had of been wearing her helmet/cycling hat like she was told she wouldn’t have been left with the Harry Potter nickname. such is life I guess.

I know. Circumstantial evidence at best.
Just like nitrogen, this is a forum chat, so we can argue as much as we like about pros and cons but we might never get an agreement.
Nevertheless we are all still friends