30 replies to this topic

[Ollie180]

i found that some race cars pump they tyres up with like helium and other gases i think hydrogen was one to make the car lighter?

has anyone does this and does it make much difference?

Edited by Ollie180, 30 July 2006 - 12:14 PM.

[R1minimagic]

the higher the pressure the more weight you can save. I think they also do that to stop them overheating as well. Not sure about hydrogen, sounds dangerous!!

[frostie]

Isn't it nitrogen?

I thought it was something to do with larger molecules, so the tyre doesn't lose pressure? Or something like that?

[Ollie180]

yeh i saw somewhere that they used to pump lorrys with hydrogen in old days or something but then they stoped becuase the tyres explloded

[StaffordSi]

yeh it is nitrogen, its so that the tyre pressure doesn't increase and decrease when the tyre's heat up and cool down quickly..... nowt to do with weight

[mini93]

also it aparently doesnt retain water like air does not sure what the advantage is but that was a point i read about

[Dan]

Well some of you have nearly got the whole story.

In top class race cars they fill the tyres with nitrogen. Doesn't really have to be nitrogen, it can be anything (except hydrogen! ) so long as it's a dry filtered gas which is relatively density stable with temperature. It's not that nitrogen doesn't retain water, it's just that once it's filtered it's definitely just nitrogen with nothing else. Air is a mixture of gasses and is roughly 80% nitrogen and contains some water vapour. The thing is that water vapour is very unstable with changes in temperature. As the tyre heats up, the water vapour expands which increases the tyre pressure dramatically. Sometimes in a race car this can reach dangerous levels but normally it just seriously and unpredictably affects the way the car handles. If you could predict exactly how the pressure in the tyre would change then you could just fill it with air but you can't so you need to exclude the water. Nothing to do with weight saving.

On a road car it seriously isn't worth it.

Interestingly it's also largely nitrogen that propels your car along the road. The nitrogen in the air expands as the chamber is heated by the burning petrol however as I've said nitrogen doesn't expand very much with changes in temperature. Water does so in theory a steam engine should produce far more power than a petrol or diesel engine as it uses water to provide the force and changes it from liquid to vapour by burning fuel, if only you could get rid of all the inefficiencies in the external combustion engine.

[Pooky]

*pooky sighs and smiles with admiration*

[jimbo_edmondo]

So i should attach a hose to my carb, ok sounds cool, now i just need a very long hose.

water in engine done, but now it won't even start i'm confused....

Edited by jimbo_edmondo, 30 July 2006 - 04:04 PM.

[Jammy]

Its starting to be a big thing in America to fill your tires with Nitrogen. The sales blurb says the Nitrogen molecules are larger than Oxygen and so can't escape through the tyre, therefore you don't lose pressure over time.

Load of carp basically.

[Jimmyarm]

I thought there was a weight advantage to it, albeit very slight. Have recollections of bike (the type you pedal) racers doing it, every gram counts !

Think they use helium rather than nitrogen though....even so water vapour would weigh more than pure Nitrogen so there would be a minimal saving.

[Jammy]

Think how much a balloon weighs, and then think of how much it weighs when full of air. The weight saving would be negligible.

[Jimmyarm]

Think how much a balloon weighs, and then think of how much it weighs when full of air. The weight saving would be negligible.

But how much does a balloon weigh ?

This is far too complicated ! Managed to ascertain that 'Air' weighs about 1.2grammes per litre (apparently). I am no scientist but I think that the weight remains static and the pressure is just more forced into the space. How many litres of air are in a tyre ?

On a road racing bike even 5g is a bonus which is why they do it.

Edited by Jimmyarm, 31 July 2006 - 02:09 PM.

[Jammy]

It doesn't matter since its a constant in this situation.

[Jimmyarm]

^^Which bit ?

Does anyone actually know how much weight you could save by filling with nitrogen/helium ?

If you havent got an exact answer then it shouldnt be dismissed as being 'negligible'.... it could be as much as 100g which when your trying to shave everything off possible is quite a bit....