Helium car tires

[J.C.MacSwell]

On 4/28/2018 at 2:52 AM, Bender said:

Behold:

The vapour pressure of water at room temperature is 0,02 bar, so if you inflated your car tires inside with 100% humidity, and then it all freezes, that would be your pressure drop.

On the other hand, a decrease in temperature from 293 K to 248 K , with a tire pressure of about 2 bar, will result in a pressure drop of over 0,3 bar (ignoring shrinkage of the tire) 

I don't think humidity is your problem.

If I am taking this correctly that is about a 30 percent drop in gauge pressure with just 2 percent attributed to change in state of water for the 45 degree drop.

The problem is exacerbated at higher temperatures, especially when free moisture is available to vapourize. If you fill the tire using air at 35C (starting point for John Cs benefit) and 100 humidity a 10 degree change, plus or minus, can produce almost as much pressure difference again as in the case of dry air. If moisture still remains at 45C the effect can become equal or greater as the tire heats up further.

I know free moisture should not to be in the tire but I suspect with many tires that could be the case (though more likely when the tire is cooler)

[dimreepr]

9 minutes ago, MigL said:

 Do you think people can tell the difference between a transistor Amp and a tube Amp, or $1000 speakers and $15000 speakers ?

1

I have to agree with this, a valve amp has much more clarity and warmth and base; speakers, on the other hand, is more prone to hype and marketing.

16 minutes ago, MigL said:

So while you may argue that the difference between air and Nitrogen is negligible, to an enthusiast, it isn't

Sorry, it seems closer to speakers for me, I honestly couldn't tell the difference when I was on a track day.

[John Cuthber]

Hi MigL

The flip side of my rather blunt personality is that I'm not easily offended. If you took out your frustrations on me that's probably better than if you took it out on someone else.

I'm aware that people spend money on stuff for dubious reasons.

If they do that knowingly, I don't mind.

I do get annoyed if someone sells  snake oil to unsuspecting victims under false pretences.

[koti]

5 hours ago, dimreepr said:

Sorry, it seems closer to speakers for me, I honestly couldn't tell the difference when I was on a track day.

There is the psychological factor too. I’ve seen drivers shave 1,5s from a 1:30’ish lap just by being convinced that their car turns better with nitrogen in tyres instead of air.

[John Cuthber]

8 minutes ago, koti said:

There is the psychological factor too. I’ve seen drivers shave 1,5s from a 1:30’ish lap just by being convinced that their car turns better with nitrogen in tyres instead of air.

Fine;  to save money, just tell them you filled the tyres with nitrogen (or kryptonite if it works better) but carry on using dry air.

[Bender]

6 hours ago, J.C.MacSwell said:

If I am taking this correctly that is about a 30 percent drop in gauge pressure with just 2 percent attributed to change in state of water for the 45 degree drop.

Typical tire pressure is 2 bar, so 15% and 1% respectively.

[Spooky_Action]

On 4/23/2018 at 10:48 PM, NimrodTheGoat said:

Overheard a conversation about car tires. One person said that instead of air they just use Nitrogen. Why use nitrogen, what is the difference? Could we therefore fill our car tires with helium to make them lighter, or even .... float? What challenges would a helium filled tire face?

Any gas other than plain old air in your automobile tires would officially slide into the dread and uselessly expensive category known as overkill. Helium would have zero advantageous effect over air. What is far more important than the type of air that's in our tires is how MUCH sir in in them! That is...correct air pressure. This drastically effects the true physics of your car's handling, safety, and of course gas mileage.

 

[J.C.MacSwell]

4 hours ago, Bender said:

Typical tire pressure is 2 bar, so 15% and 1% respectively.

Right so 2 bar gauge is 3 bar. Should the drop not then be closer to .45 bar? (22.5%)

[Frank]

18 hours ago, John Cuthber said:

I seem to recall hearing that the translators struggle to translate the common English phrase "room temperature" into French because there's no simple equivalent.

Is that true?

I would have gone with the literal "température de la pièce", but google used "ambiante" which it translated back to

température ambiante -> ambient temperature

"room temperature" in french - Google Search:  https://www.google.com/search?q="room+temperature"+in+french

Curiosity got the better of me.  To me, ambient temperature is dependent on (external and unknown) conditions, whereas room temperature is a fairly specific range.

 

[Bender]

10 hours ago, J.C.MacSwell said:

Right so 2 bar gauge is 3 bar. Should the drop not then be closer to .45 bar? (22.5%)

Correct. I completely forgot to take the difference between absolute pressure and overpressure into account.

Which brings us to an additional effect: ambient pressure. When in a low barometric pressure region, the ambient pressure can be 0,1 bar lower than in a region with high barometric pressure, resulting in a tire pressure which is 0,1 bar higher. The problem gets worse when driving to high altitudes.

I just installed my summer tires and inflated them with a manual pump while it is quite rainy outside. I guess some water vapour got in. It occured to me that if water vapour is slower to escape from the tire, it could accumulate over the years. Given how small the effect is, I'm not really worried, though. 

[Frank]

2 hours ago, Bender said:

Correct. I completely forgot to take the difference between absolute pressure and overpressure into account.

I just installed my summer tires and inflated them with a manual pump while it is quite rainy outside. I guess some water vapour got in. It occured to me that if water vapour is slower to escape from the tire, it could accumulate over the years. Given how small the effect is, I'm not really worried, though. 

 

Well, nitrogen or other gases will also change pressure with temperature, but the water vapour claim I'm still unclear on.  Why would it increase with increasing pressure?

I understand that the upper bound of vapour pressure in a tire is already in the 1% region, but now I wonder what the effect of compressing the air to 8 bar for example, and letting it cool to standard temperature would be.  I know from experience that water will condense, so even less moisture/water vapour will get into the tire.  I haven't found the formula to calculate this effect.

 

Also, "température de l'air ambiant" seems a better translation to ambient temperature since "température ambiante" seems to translate directly to room temperature.  Being francophone in an anglophone area, the anglicized "température de la pièce" version seems more accurate.

 

BTW, I +1 bender's previous post for illustrating the size of helium tire needed and showing that condensation of water vapour is insignificant next to gas pressure change due to temperature.

 

Found charts here: Compressed Air and Water Content:  https://www.engineeringtoolbox.com/water-content-compressed-air-d_1275.html

 

[Bender]

58 minutes ago, Frank said:

Well, nitrogen or other gases will also change pressure with temperature, but the water vapour claim I'm still unclear on.  Why would it increase with increasing pressure?

I understand that the upper bound of vapour pressure in a tire is already in the 1% region, but now I wonder what the effect of compressing the air to 8 bar for example, and letting it cool to standard temperature would be.  I know from experience that water will condense, so even less moisture/water vapour will get into the tire.  I haven't found the formula to calculate this effect.

You have found the curves, but it can also be calculated. The vapour pressure is (mostly) independent of the total pressure. That means that in the same volume (and temperature) of saturated air, you'll have the same mass of water.

However, since there is more air at a higher pressure, the ratio of water to air decreases.

Eg: if you half the volume of saturated air (isothermically: at constant temperatuur), the amount of water vapour it can contain also halves,  but the amount of "free air" remains constant. The percentage of water vapour halves.

The curves in the link are also in "free m3" which is not the actual volume of the air, but the volume the air would have in standard temperature and pressure.

For vapour pressure in function of temperature, you always need curves or tables, since it is highly nonlinear.

Edited April 30, 2018 by Bender

[Frank]

5 minutes ago, Bender said:

You have found the curves, but it can also be calculated. The vapour pressure is (mostly) independent of the total pressure. That means that in the same volume (and temperature) of saturated air, you'll have the same mass of water.

Right, the vapour pressure doesn't increase with tire pressure, so even with water available in the tire, vapour pressure is limited and condensing water vapour doesn't change pressure very much at all.  Also, as the tire heats up, it's pressure increases limiting the effect of water vapour compared to free air temperature vapour pressure increase.

Based on the example given, compressing the air to 8 bar isothermically would remove moisture from the tire to 0.19/1.7 to about 11% that of saturated air.  Keeping water out would help (though not very significantly) by limiting the amount of extra water available in the tire to create extra vapour pressure. 

 

Consumer report showed the diffusion rate, 3.5 psi loss for air over 1 year and 2.2 psi for nitrogen: Nitrogen in tires - Q&A:  https://www.consumerreports.org/cro/news/2007/10/nitrogen-in-tires-q-a/index.htm

Conclusion: Not worth paying extra for nitrogen, check air pressure regularly.

 

[J.C.MacSwell]

5 hours ago, Bender said:

Correct. I completely forgot to take the difference between absolute pressure and overpressure into account.

Which brings us to an additional effect: ambient pressure. When in a low barometric pressure region, the ambient pressure can be 0,1 bar lower than in a region with high barometric pressure, resulting in a tire pressure which is 0,1 bar higher. The problem gets worse when driving to high altitudes.

I just installed my summer tires and inflated them with a manual pump while it is quite rainy outside. I guess some water vapour got in. It occured to me that if water vapour is slower to escape from the tire, it could accumulate over the years. Given how small the effect is, I'm not really worried, though. 

I think you can assume 100% humidity in those conditions. Since your source is at 1 bar and assuming it all goes in until it is 3 bar (2 bar gauge) wouldn't 2/3 of the vapour have condensed out once the tire gets back to ambient temperature?

Edit: Manual pump for installing 4 tires? I wouldn't want to mess with you!

Edited April 30, 2018 by J.C.MacSwell

[Bender]

55 minutes ago, J.C.MacSwell said:

Edit: Manual pump for installing 4 tires? I wouldn't want to mess with you!

I keep my extra tires on an extra set of naves, so they are still almost at the right pressure. It would be pretty hard (if not impossible) to inflate a tubeless car tire manually from 0 gauge (which needs a starting pressure before it is sealed). It also avoids all the equipment necessary to actually get them on their nave or to balance them afterwards.

[J.C.MacSwell]

3 hours ago, Bender said:

I keep my extra tires on an extra set of naves, so they are still almost at the right pressure. It would be pretty hard (if not impossible) to inflate a tubeless car tire manually from 0 gauge (which needs a starting pressure before it is sealed). It also avoids all the equipment necessary to actually get them on their nave or to balance them afterwards.

Gotcha...so it's not your heavy day workout for the week!

[Bender]

Luckily not. One of them was halfway deflated  (have to check that again tomorrow), and I lost quite some sweat on that one. 

[Bender]

Ok , I had to put two winter tires back on, because the one that was mostly deflated had again lost some pressure. When checking the pressure of the winter tires, it was about 0,2 bar too high, fitting nicely with a 20K temperature difference between now and when I installed them in november. It certainly overshadowed any air loss due to diffusion.

Interesting. I had never paid attention to this effect before.

Edited May 2, 2018 by Bender

[Neil Obstat]

On 4/26/2018 at 11:53 AM, John Cuthber said:

Unless there's liquid water in the tyre, the vapour pressure of water is irrelevant.

If there is liquid water in the tyre someone has screwed up so badly that the point is moot.

All air compressors generate liquid water in the storage tank. The water vapor in the air gets included with the compression action.

Then after it's in the storage tank, as air is taken out for use, the temperature drops and condensation precipitates to the bottom of the storage tank.

So there is increased humidity in the storage tank, which must be drained off or else it builds up.

You can install a dryer in the system that extracts the moisture, but service stations generally don't bother with that detail because it costs money.

Any tire service technician can tell you that most of the time when he removes a tire from a rim he finds water inside. 

Moisture inside the tire reacts with steel rims causing corrosion (rust) on the rim, which over time can eat through the whole thing, ruining it.

A product called "slime" is supposed to work for a sealant inside your pneumatic tires but ask a tire pro, he'll caution against leaving slime inside because it corrodes your rims.

But how to get it OUT? 

That's a good question! How do you get water out, too?

Try turning the tire around so that the valve stem is at the bottom where you can let off air pressure to extract collected water. Just TRY!

At local service stations compressed air is provided by a dedicated compressor that has no storage tank, so you get the moisture immediately.

 

Edited June 5, 2018 by Neil Obstat

[Bender]

20 hours ago, Neil Obstat said:

Try turning the tire around so that the valve stem is at the bottom where you can let off air pressure to extract collected water. Just TRY!

That's pretty difficult, since the value is at the inside of the tire.

 

[John Cuthber]

20 hours ago, Neil Obstat said:

All air compressors generate liquid water in the storage tank. The water vapor in the air gets included with the compression action.

Then after it's in the storage tank, as air is taken out for use, the temperature drops and condensation precipitates to the bottom of the storage tank.

So there is increased humidity in the storage tank, which must be drained off or else it builds up.

You can install a dryer in the system that extracts the moisture, but service stations generally don't bother with that detail because it costs money.

Any tire service technician can tell you that most of the time when he removes a tire from a rim he finds water inside. 

Moisture inside the tire reacts with steel rims causing corrosion (rust) on the rim, which over time can eat through the whole thing, ruining it.

A product called "slime" is supposed to work for a sealant inside your pneumatic tires but ask a tire pro, he'll caution against leaving slime inside because it corrodes your rims.

But how to get it OUT? 

That's a good question! How do you get water out, too?

Try turning the tire around so that the valve stem is at the bottom where you can let off air pressure to extract collected water. Just TRY!

At local service stations compressed air is provided by a dedicated compressor that has no storage tank, so you get the moisture immediately.

 

 

 

On 4/28/2018 at 1:27 PM, John Cuthber said:

It's very easy to provide air that's "dry enough" for this application; you just compress the air to a pressure that's higher then the pressure you use in the tyre, wait for any water to condense, and then expand the air down to the right pressure. The relative humidity will fall with the pressure.

[Neil Obstat]

6 hours ago, Bender said:

That's pretty difficult, since the valve is at the inside of the tire.

Thank you. (I made "value" into "valve" -- correct?)

6 hours ago, John Cuthber said:

It's very easy to provide air that's "dry enough" for this application; you just compress the air to a pressure that's higher then the pressure you use in the tyre, wait for any water to condense, and then expand the air down to the right pressure. The relative humidity will fall with the pressure.

Easy like when you have your own compressor? How about out on the road and you go to a service station for air and their pump has no storage tank but the air comes straight from the compressor into the hose, so you have no control over the pressure -- take it or leave it!  In any case, how do you remove water once it's in your tire? 

Edited June 7, 2018 by Neil Obstat

[Bender]

Heat the tire and release the hot, moist air.

[John Cuthber]

4 hours ago, Neil Obstat said:

Easy like when you have your own compressor? How about out on the road and you go to a service station for air and their pump has no storage tank but the air comes straight from the compressor into the hose, so you have no control over the pressure -- take it or leave it!  

What if you choose to use nitrogen, but the service station doesn't have it?

 

[Endy0816]

10 hours ago, John Cuthber said:

What if you choose to use nitrogen, but the service station doesn't have it?

What are they offering if not Nitrogen?