Nitrogen PSI ?

[sapper]

I had new tyres fitted today and the chap I used filled them with nitrogen. I wasn't there when he inflated them so he took a guess and filled them all with nitrogen to 36psi so I could adjust to the correct pressure myself.
So the question is ,, what psi should I use with nitrogen?

[phazed]

Without googling I reckon the same as cooking air.

[sapper]

I was thinking the same but haven't given it much thought before today. On a separate topic, phased, adores your front splitter make much of an improvement?

[wuckfitracing]

Same as normal pressures. Nitrogen has no water content that expands and contracts with temp.

[Englishman]

Yes, whatever you usually set the tyres to when cold.

When I had tyres changed on the Tuscan a couple of weeks ago they inflated with Nitrogen without asking. Don't believe it will make much difference in road tyres though.

[anonymous-user]

wuckfitracing said:

Same as normal pressures. Nitrogen has no water content that expands and contracts with temp.

Not quite the right answer. Set them at what they were previously when hot...

[Englishman]

Not sure why you say that, air, oxygen and nitrogen all behave exactly the same in terms of pressure change with temperature change. Therefore set tyre pressures as per normal.

However, air does contain moisture, nitrogen does not. At normal car tyre temperatures any water occupies very little volume as its is in liquid form and hence contributes a negligible pressure inside a tyre. However if the tyre gets really hot, approaching or over boiling point or water, e.g, aircraft landing or competitive motorsport, the water in a tyre becomes a gas and increases pressure in the tyre. Hence the reason aircraft tyres are filled with Nitrogen to keep at a steady pressure during take-off and landing.

Apologies, its the physicist education coming out!

[wuckfitracing]

How would you know what previous pressures they were when they were hot, being as they are new tyres. also what temp is defined as hot. I dont mean to be awkward but just for my info as i assumed them to be checked when cold.

[RichB]

Englishman said:

Not sure why you say that, air, oxygen and nitrogen all behave exactly the same in terms of pressure change with temperature change. Therefore set tyre pressures as per normal.

However, air does contain moisture, nitrogen does not. At normal car tyre temperatures any water occupies very little volume as its is in liquid form and hence contributes a negligible pressure inside a tyre. However if the tyre gets really hot, approaching or over boiling point or water, e.g, aircraft landing or competitive motorsport, the water in a tyre becomes a gas and increases pressure in the tyre. Hence the reason aircraft tyres are filled with Nitrogen to keep at a steady pressure during take-off and landing.

Apologies, its the physicist education coming out!

Yeah... the alternative theory is that they it is used in aviation because Nitrogen is an inert gas and therefore safer, same reason f1 copied. Since then it's become the fashionable thing to do. Google is full of both theories.

[sapper]

wuckfitracing said:

How would you know what previous pressures they were when they were hot, being as they are new tyres. also what temp is defined as hot. I dont mean to be awkward but just for my info as i assumed them to be checked when cold.

Yes mate, tyres checked when cold.
My thinking is (someone more educated please tell me if I'm wrong) until recently we filled with air .
Our tyre manufacturers recommended pressure based on air 78%ni 21%O2 and some %. stuff.

So if O2 and stuff is smaller than Nitrogen and escapes easier through the tyre have they taken this into consideration when using nitrogen as a filling and therefore recommended pressures.
So, when checking pressure when cold should you allow for increased pressure when hot as nitrogen expands more than O2 & stuff?

[phazed]

When they tested nitrogen on 5th gear it wasn't as stable as you would think.

Their conclusion generally was stick to air.

[sapper]

phazed said:

When they tested nitrogen on 5th gear it wasn't as stable as you would think.

Their conclusion generally was stick to air.

Bugger

[ChilliWhizz]

I use helium in mine, it significantly reduces the unsprung weight, making a noticeable difference on bumpy surfaces.

[QBee]

I had heard that Derek fills his tyres with nitrous oxide. Makes it a laugh to drive, apparently......

[Dr Mike Oxgreen]

I prefer to use a carefully chosen mixture of gases in the following precise proportions:

• 78% Nitrogen
• 21% Oxygen
• 0.9% Argon
• 0.04% Carbon dioxide

[Bassfiend229hp]

Dr Mike Oxgreen said:

I prefer to use a carefully chosen mixture of gases in the following precise proportions:

• 78% Nitrogen
• 21% Oxygen
• 0.9% Argon
• 0.04% Carbon dioxide

Hey! You sod! I use that ... I was keeping it a secret! How did you find out about it?

[ClassiChimi]

QBee said:

I had heard that Derek fills his tyres with nitrous oxide. Makes it a laugh to drive, apparently......

That's rather amusing that is,

I'd have thought, unless you are prone to driving flat out around turns for more than say 20 mins at a time, it's unnessasary.
Cool but unnessasary.

I'd also say recommended pressures are worth playing with anyway, different tyre makes etc,

I tend to run soft on the roads to get some compliance at slow speeds,
But then I'm on a road tyre which is hard so it's as much about what tyre etc.

[bobfather]

TVRMs said:

wuckfitracing said:

Same as normal pressures. Nitrogen has no water content that expands and contracts with temp.

Not quite the right answer. Set them at what they were previously when hot...

Correct, the reason the book pressure states 'cold' is because the optimum pressure will be achieve as the inflation gas expands due to heat. Dry N2 still expands but only a fraction of the amount anticipated by the 'cold' book pressure.

This is popular among the max power lot so I'm guessing there are thousands of young boys driving on under inflated tyres as a result of this misunderstanding