Naked Science Forum
General Science => General Science => Topic started by: Cole Hawkins on 03/11/2008 22:36:41
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Cole Hawkins asked the Naked Scientists:
Hi,
Two questions:
1. Does filling car tyres with nitrogen make sense for a passenger car and why is this argument made?
2. Now that you have a Naked Scientist T-shirt, what do they look like and how (maybe) can I order one?
Thanks,
Cole Hawkins
California, USA
What do you think?
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I had never heard of this idea before this question so I had a think and came to the conclusion that as nitrogen and oxygen have very closely similar molecular weights the only advantage could be the removal of the reactive element oxygen which could tend to react with the tyre material and degrade it. Nitrogen is a relatively inert gas.
Googling +car +tyres +nitrogen produces lots of references that confirm this theory many of which suggest that any benefits for ordinary road cars are negligable and I would tend to agree with this.
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It is claimed that nitrogen filled tyres maintain their pressure for longer than air filled tyres.
It is necessary to have tyres at the correct pressure for optimum fuel economy
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Tyre pressure has been long neglected in car design. It is comparatively easy to monitor tyre pressure constantly in a moving vehicle and every new car could include it as a feature. Nevertheless they bombard us with SatNav, multiple CD players and automatically adjusted seats in the adverts.
The tyre is the vital interface with the ground. Knowledge of pressure can help with fuel efficiency in the long term and a timely warning of pressure changes can give protection against the effect of leaks / overheating / blowouts.
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http://www.thenakedscientists.com/forum/index.php?topic=8041.0
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My car has an indication of incorrect tyre pressure but it is relativley crude and depends of measuring the relative rotation speed of eheels rather than a direct measure of the pressures themselves. Good cheep pressure sensors may have been around for a long time but the problem of conecting them to power and data transfer from a rotating wheel is not simple and still relatively exopensive.
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I think the cost would outweigh any advantages.
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So a multi CD player is worth the money, instead, is it?
You could save at least £20 for each new tyre if you could ensure it would last its proper life. One blowout in a driver's lifetime would surely be worthwhile preventing.
They can put oxygen sensors in the red hot exhaust gases because fuel and pollution are big, current issues. I bet it could be done for not many quid per wheel. Power supply need not be an issue - the mean power could be milliWatts and you could use inductive coupling both for power in and signal out.
No, they're not sexy enough; that's the reason.
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I was referring to the cost of separating out the nitrogen.
I can see no possibility of additional tyre life if it were filled with nitrogen. The wear on a tyre is on the outside; the tread, which is exposed to the air! Nitrogen on the inside will have no effect on the external surface in contact with the road surface.
Blowouts are expensive, and covering a great many miles, as I do, I have had my fair share of them. Such was true of the blowout I had at 5.30am one Saturday morning half way from London to Harrogate. Not only the cost of getting the blowout dealt with, but also the fact that I was unable to get a mobile 24hr unit to sort the problem until 8.00am. But would nitrogen have kept the tyre inflated after I ran over a screw in the road?
As for tyre pressures, simple to check with a tyre pressure gauge. Takes a few mins.
Far too many computers and electronic gadgets on vehicles as it is these days.
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simple to check with a tyre pressure gauge.
True, on the face of it but I know many many people for whom that is a major problem - they can't check the oil or the wash bottle either. And when it's rained every time I used the car for a week, it's too much trouble for me too.
The Nitrogen thing is just a waste of time.
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I typically fill my tires with 80% Nitrogen, 20% Oxygen [;D]
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Blimey! Where did you dredge this one up.
Maybe we could sequester CO2 in them.
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I thought it was at the top of the list.
But... perhaps it was just one of those random posts which are sometimes interesting.
If the post about the balloons is valid... then it is likely that 100% CO2 would leak out of the tires quicker than air. And, CO2 is a heavier molecule than air (Oxygen/Nitrogen). So, CO2 is probably only moderate at best.
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Yesterday on the F1 from rainy Montreal they mentioned that motor-racing car tyres are filled with Nitrogen rather than air. These tyres are used for less than two hours so I don't think it's a long term degradation issue. Does it make it easier to model expansion/temperature changes?
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According to a number of websites it is the lack of change of pressure with temperature that is the key element for F1 tyres. I think the main factor is that the Nitrogen is dry and dry nitrogen is easily available. Other gases have been used in the past - I think Ferrari used some exotic mix containg fluorocarbons at some time in the past.
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My tractor's tires are filled with antifreeze, but I think that's for a different reason [:D]
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"According to a number of websites it is the lack of change of pressure with temperature that is the key element for F1 tyres."
nitrogen ( like most gases) obeys this
http://en.wikipedia.org/wiki/Charles's_law
quite well for the sort of temperature and pressures in tyres
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"According to a number of websites it is the lack of change of pressure with temperature that is the key element for F1 tyres."
nitrogen ( like most gases) obeys this
http://en.wikipedia.org/wiki/Charles's_law
quite well for the sort of temperature and pressures in tyres
Yeah! It only took TNS 2.5 years to figure this one out!
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"According to a number of websites it is the lack of change of pressure with temperature that is the key element for F1 tyres."
nitrogen ( like most gases) obeys this
http://en.wikipedia.org/wiki/Charles's_law
quite well for the sort of temperature and pressures in tyres
Yeah! It only took TNS 2.5 years to figure this one out!
It may have taken that long for you to post it, but it took rather less than a day for us to figure it out.
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"Dry" gas sounds like an idea. I know that air compressors and air brake systems can pick up some moisture pretty quickly. However, I would think you could dry the air easily enough.
If rotating mass is an issue.
Why not fill them with Helium?
It probably wouldn't reduce the overall mass of the vehicle much so it shouldn't affect traction. However, it would reduce the rotating mass somewhat.
I'm sure it would leach out pretty quickly, but for racing, as you mentioned, all one has to do is finish the race (or half the race if tires are changed).
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"According to a number of websites it is the lack of change of pressure with temperature that is the key element for F1 tyres."
nitrogen ( like most gases) obeys this
http://en.wikipedia.org/wiki/Charles's_law
quite well for the sort of temperature and pressures in tyres
Yeah! It only took TNS 2.5 years to figure this one out!
It may have taken that long for you to post it, but it took rather less than a day for us to figure it out.
Actually, it's really four years including the previous thread [;D]
Maybe we should have had it rethreaded?
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BC, the key factor is "DRY" not specifically the gas. With changing temperature the partial pressure from water vapour is VERY significant, especially in F1. I was aware of the gas laws! As I said DRY nitrogen is readily available.
The use of complex gases by Ferrari was to do with using the gases to cool the tyres (according to websites) by conducting heat to the metal part of the wheel.
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I don't think it have any effects
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Notwithstanding the fact that the "point" of f1 is to drive round in circles, they are not idiots.
They would know that you need to remove at least some of the water from air before pumping it into tyres (other wise you end up with some liquid water in there which would be horrid).
As I mentioned a few years ago, just compressing the air, storing it in a tank , and then delivering it to a tyre at a lower pressure than the tank pressure would be sufficient to do that. The F1 folks would have worked it out too. They would know you don't need to use nitrogen, nor do you need very dry air.
Tyres run hot so the problem is even less stringent that it first looks.
As long as you don't reach the saturated vapour pressure, water vapour obeys Charles' law quite well too.
If Ferrari has looked at a table of gas properties that would have found that hydrogen and helium carry heat rather well.
The generators in my local power station were enclosed in sealed vessels full of hydrogen in order to cool them.
More complicated and heavier gases are generally going to be worse conductors of heat.
It's perfectly possible that Ferrari are deliberately misleading the opposition.
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I suppose the composition of the gas could increase the rate of heat conduction into the wheels, but would it make an appreciable difference? I'm not even sure they would want to do that. They seem to go to a lot of trouble to keep the tires as hot as possible.
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Good point. They at least like warm tires.
Conducting heat away from the brakes is another issue though.
If one is wanting to conduct heat from the tire to the rim, what about adding a layer of aluminum foil to the inner surface of the tires.