Inflating tyres with dry nitrogen

[Prithvi]

Had filled my Octy with Nitro and the pressure dropped in a week a lot. Yes the ride felt more smoother & comfortable. But its not worth the amount they charge.

Have since stuck to our old good AIR. No more nitro for me. IMHO. Totally crap

[janitha]

Originally Posted by Prithvi

Had filled my Octy with Nitro and the pressure dropped in a week a lot. Yes the ride felt more smoother & comfortable. But its not worth the amount they charge.

Have since stuck to our old good AIR. No more nitro for me. IMHO. Totally crap

Due to the drop in pressure?

[watashi75]

Originally Posted by Thad E Ginathom

But... do some gases expand more than others?

This question merits no thought. Once you have filled the tyre with a gas be it nitrogen, oxygen or any plain gen to the required pressure, the volume will remain constant. The only variables that can possibly change are pressure and temperature. Hence, for any gas inside the tyre, if temperature increases by x%, the pressure will also increase by x%.

With regards to dry vs wet air, water vapor has a molecular weight of 18 as compared to Nitrogen's 28. So tyres with more vapor content are actually lighter than the drier version. But what happens is that moisture condenses at low temperature and evaporates at higher temperature leading to fluctuations in tyre pressure at hot and cold conditions. However, for the same temperature the pressure is going to be the same. If you could actually fill tyres with dry air, the effect would be same as if you filled it with "dry" Nitrogen.

People who use Nitrogen also say that it leaks less. But that is only for leakage through the rubber itself. More often than not air leaks through gaps in the rims and valves.

[gostel]

Well said watashi, you are dot on and couldn't agree more with you.

Whatever we were taught at school with p, v, t, was done with that fine print: held true for ideal gases! Water vapor and carbon dioxide are far from ideal. But then another thought crossed my mind. Is it necessary to invoke the gas laws to explain all the varied observations on this nitrogen filling matter?
For example, give a thought to this: the attendant at the pump had filled my tyres using a digital gauge and a preset controller; leaving no room for doubt. However, soon after this the SA at a MASS found that my tyres had different pressures and all of them less than the stipulated 30psi. What had gone wrong? Nothing serious really, as I discovered the next time we went for an air-fill. The attendant would retract the air nozzle in a rather sloppy manner thereby leaking a goodly amount of pressure.
What I mean to point out is that the experiment here is grossly riddled with the human factor hence making inferences and explaining the various phenomena makes for a good source of amusement, and I am loving every bit of it! I would often doze off in the chemistry classes and this thread sort of compensates for all that I missed at that time. Thanks guys!

[anupmathur]

Haha, gostel, same case here - I enjoy reading what gets posted at this thread!

However, when you say that there is little room for doubt BECAUSE a digital gauge was used along with 'auto' cutoff I would disagree.

Originally Posted by gostel

...
For example, give a thought to this: the attendant at the pump had filled my tyres using a digital gauge and a preset controller; leaving no room for doubt. ....

A digital display (vs an analogue display) in no way guarantees more accuracy. Nor does the auto cutoff feature. It is the 'sensors' and transducers that determine the accuracy of any equipment, and if these are not regularly calibrated/adjusted against standard/reference gauges there can be large errors present!
It is in this area that most of our equipment is dubious and untrustworthy!

[gostel]

Oops anupji, did I make a slip? Gosh Sir Anupji, if I didn't know about gauges and calibration then I ought to jump into a well. However, my case rests on the fact that the four tyres, all had different pressures in them, which I humbly believe were due to human factor. Now just imagine somebody filling free air carelessly, and another somebody filling expensive nitrogen very carefully. The reason for observed differences could be due to the human factor (which includes quality and calibration of gauges used).
About the argument on digital versus analog: it is not the accuracy in question, but the repeatability that is better ensured by digital equipment. A digital instrument will be wrong every time and by the same amount. For analogy: you know very well that a stopped watch will show the correct time twice a day, don't you?
Nonetheless it is so nice to hear (or read) from you, sir, that being on T-BHP is a truly rewarding experience.

[watashi75]

Not to forget, the reading on the analog meter depends on your perspective. I would advise you not to shake your head while taking a reading.

[inwester]

In the recent times, coming across facebook and forums I've learned that many people have a fad of filling up tires with Nitrogen. Sure, it costs more than regular air, then you can also claim more mileage, less wear, less leakage, more comfort and better ride, and yeah, of course the bragging rights.

Can't speak for everyone, but if I remember correctly, regular air is 78% Nitrogen?

So theoretically for improved fuel efficiency either friction has to be less or weight has to be less. Now friction only depends on the tire surface and thread pattern, so basically no effect putting Nitrogen. So, then it has to be lesser weight, right, well, yeah, we are talking less weight for the remaining 22% of air in four tires. It's got to be less than a few grams. I can't help, but, stop laughing.

Now, air leakage. Assuming we all still run our cars on Petrol/Diesel you have to visit the pump at least every 2 weeks, if not more. So please check air, in most cases it costs nothing and you probably won't have to fill up as well.

Oh yeah, the temperature, fire resistance, blah blah. While I can see how this could be a serious concern in Formula 1, but how many of us have a 600 horse power engine, revving at 8000 rpm or more, driving in race tracks on ultra high performance tires for 3-4 hours non-stop? Or how many of us drives a massive lorry or a trailer with 18 wheels where tire pressure needs to be in the 100 psi range. I guess none in this forum.

What I'm trying to say is that there is only anecdotal evidence (if at all) that points out that Nitrogen is better than air. For all practical purposes it is the SAME! Save yourselves some time and money.

For me good 'ol air just works fine.

[gigy]

It feels good after spending money.

[sgiitk]

@watashi: What messes you up badly with service centre/petrol pump air is the moisture content. This tends to collect inside the tyre and then on warming up changes the pressure far more than pure gas would.

I always use a small pump (about Rs.800) and fill up at home into cold tyres.

[watashi75]

Originally Posted by sgiitk

@watashi: What messes you up badly with service centre/petrol pump air is the moisture content. This tends to collect inside the tyre and then on warming up changes the pressure far more than pure gas would.

I hope you are talking about the same thing as I am. Because there is nothing like some gases expand more than others.

Consider a tyre filled with pure water vapor at 30psi and another tyre filled with nitrogen at 30 psi. If the temperature is increased by 10 % (in absolute Kelvin), the pressure of both tyres will increase by 10% to 33 psi. This follows from the gas law -

PV = nRT

In this scenario V,n,R are constant. So pressure will be directly proportional to temperature.

[anupmathur]

Originally Posted by sgiitk

..
I always use a small pump (about Rs.800) and fill up at home into cold tyres.

I wonder if a small pump prevents condensate from being pumped into a tyre!?
And it's not the pump alone, what is more important is an accurate gauge to check the pressure with.

My 'Slime' compressor needs at least two fifteen minute cooling breaks for pressing up Scorpio tyres to 32 psi! Total time goes to over an hour per tyre, starting from flat!

[emkay456]

Atleast for last one year I have used nitrogen and only needed to refill twice, the latest being last week.
So I am happy spending 100 bucks twice a year.

[sgiitk]

Originally Posted by anupmathur

I wonder if a small pump prevents condensate from being pumped into a tyre!?
And it's not the pump alone, what is more important is an accurate gauge to check the pressure with.

My 'Slime' compressor needs at least two fifteen minute cooling breaks for pressing up Scorpio tyres to 32 psi! Total time goes to over an hour per tyre, starting from flat!

The air in your house is not saturated with water, while around a car washing facility it is.

I have been buying cheap unbranded pumps (I guess chinese) for the past decade plus, and they easily last me for 5+ years. I do all the four tyres on the trot. Before this I used a foot pump.

[Thad E Ginathom]

The air around my house is saturated with water!

That's Chennai humidity for you!