Strange Tire Pressure

[Dunerunner]

Gremlins !!!

[JIM VINYARD]

Try a different tire gauge (NEW). Maybe your tire gauge is bad or you aired up your tires while the sun was on some of them.

[pattison]

Originally Posted by jonnysan

I have to comment on this one.

Nicholas....ALL gases EXPAND when heated bar none. The air used in a tire has only 20% less N2 concentration than "4- 9's" N2 from a bottle along with a slight amount of water vapor if the air isn't dried...not enough advantage to say so in my opinion and surely not worth what they will charge for it....that's a fact Jack.

Keep your life uncomplicated....use AIR!

Actually gas does not expand with temp change.... it is the moisture content/water vapor that expands with heat... so the less moisture content in the gas the less expansion......
That is one reason why nitrogen is used. The other two reasons are:
-nitrogen molecules are larger and less likely to leach through the tire
-Nitrogen is totally inert and won’t react with any of the (+170) chemical compounds in the tire (who know what crap is in the compressed air).
graham

[Old smart]

Originally Posted by pattison

Actually gas does not expand with temp change.... it is the moisture content/water vapor that expands with heat... so the less moisture content in the gas the less expansion......
That is one reason why nitrogen is used. The other two reasons are:
-nitrogen molecules are larger and less likely to leach through the tire
-Nitrogen is totally inert and won’t react with any of the (+170) chemical compounds in the tire (who know what crap is in the compressed air).
graham

Wow! Reference Boyle's Law concerning gasses! Therein there are three variables: pressure, temperature, and volume. If any one is a constant, the other two vary inverse-proportionately. Any combination works. Nitrogen is a gas; air is a gas; water vapor is a gas. BTW, the interior volume of a tire is a constant.

[SmartCard]

Originally Posted by Old smart

Wow! Reference Boyle's Law concerning gasses! Therein there are three variables: pressure, temperature, and volume. If any one is a constant, the other two vary proportionately. Any combination works. Nitrogen is a gas; air is a gas; water vapor is a gas. BTW, the interior volume of a tire is a constant.

that's right! Moreover, the pressure of any ideal gas (nitrogen, oxygen, carbon dioxide, water - main components of air - are all ideal gases) depends on the number of gas molecules, not the type of gas. So a tire filled with equal amounts of air or pure nitrogen at a given temp will produce the exact same pressure!

The only perceived benefits of pure dry nitrogen within a tire would be increased longevity of the tire components I would think. Now, if you used helium, you would have the added bonus of a slightly lighter tire - that could be worthwhile!

[marck]

Originally Posted by SmartCard

Now, if you used helium, you would have the added bonus of a slightly lighter tire - that could be worthwhile!

Hahaha. Good luck keeping it in the tire!

Originally Posted by pattison

-nitrogen molecules are larger and less likely to leach through the tire

Only slightly. And one anomoly is CO2. It's larger than N2 but leaks through rubber like crazy! Many bicyclists use this in their mini-power-inflators that use a CO2 cartidge. They are amazed to find their tires flat sooner than usual.

Molecular leak rates usually vary according to the cube root of the gas's molecular weight. I didn't believe it until I checked a Parker O-ring Tech Bulletin on gas diffusion through O-ring compounds.

[Westfield 11]

Since air is over 70%? nitrogen, the only benefit to pure Nitrogen is the low humidity. That said we always used nitro in our heavy jet tires and also in the race tires used by the factory teams we worked with in AMA racing. Since the bike tires were all hand made they leaked air like crazy, the nitro helped that a bit.

If one tire is truly reaching a higher pressure after driving I would check my alignment. An optical pyrometer will show which area on the tire is hottest, this will tell you what suspension/chassis changes need to be made. We did a lot of this in my racing career. One clue is that the variation occurs on the front tires, the ones that can have toe-in and toe-out issues.

Another thing to think about is the type of pressure gauge. If you have a "stick" type gauge, make sure to press the stick back into the body of the gauge while you are holding pressure. It is VERY common to have the stick fly out past the point where the internal plunger stops. This will easily give a 3 PSI error or even more.

[Old smart]

Originally Posted by sixcrows

... What the hell? ...

Working back to the origin of the thread, and all that has followed, I would recommend that a smart owner invest (yup, "invest") in a good, reliable, consistant, bullet-proof pressure gauge. The cheap pencil-type gauges with a marked rod that squirts out of the end are notoriously inaccurate. A lot of the small dial-type gauges are not much better once they have been knocked-about.

Considering how much a smart's comfort and handling is affected by tire pressure, I can recommend after my own use of a "0-30," the INTERCOMP 0-60 psi, dial gauge with a pigtail and bleed-off valve (or the equivalent if you can find one). $35 well spent - truely pro-grade.

Pegasus -Tire Pressure Gauges 0-60psi