Tire fill: Something different in the air

[CapriRacer]

Originally Posted by oil pan 4

.....This will be part of the non road test, fill the tire at night to a set pressure, lay it down on the ground where the sun will hit it, let it get good and hot to simulate being driven and check pressure again. I am not expecting much to happen......

Some things you might not be aware of:

Tires, when first mounted, expand greatly in the first 24 hours - to the point where people who do this regularly add 2 to 3 psi over the target, so that it will be on target after the tire grows.

Second, even tires that have been deflated, then re-inflated suffer from a lesser form of this.

So I'd recommend mounting the tire for 24 hours before starting the test and readjusting the pressure at the start. That reading should be taken in a stable environment - room temperature.

You need to have a sensitive pressure gauge. I think one with tenths of a psi will work.

And lastly, as an end point, you ought to return the tire to its original condition (at room temperature) and check for leakage by measuring the pressure 24 hours after it is returned to that stable environment. THAT reading should be the same as the first one. If not, you have leakage that invalidates the test.

[oil pan 4]

Ok these are all tires that are between several years old, to brand new tires mounted on the rim within the last month or so but have seen 0road miles.
My gauge does half psi.

[jakobnev]

I'm mostly interested in seeing what the tires look like with vacuum in them.

[oil pan 4]

I dont try to pull a high vacuum. I figure tires are made to hold pressure in, not the other way around.
I put the air powered vacuum pump on it and let it pull air out till the side walls suck in a little bit.
Then it takes a lot of CO2 to bring them up to 30psig.

So far they have been holding CO2 like a champ.

Next step will be to bleed the CO2 down to 15psig, then bring it up to 40psig with R-404a.

Next time I fill with CO2 I will weigh the bottle before and after.

[oil pan 4]

The CO2 test was on going for a few weeks. About as exciting at watching grass grow.
Tired of that I decided to spice things up a bit.
So I deflated my CO2 test tire from 40psig to 15psig. Then brought them up to 40psig with R-404a.
Then rolled it out in the sun and dropped a sheet of aluminum in front of the tire to act as a reflector to heat the tire up faster. Almost immediately the tire surface temperature jumped up 50°F. The back side of the tire heated up 12°F in about 5 minutes.
This translated to a 2psi pressure rise.
An increase of 5 to 6 degrees F on the shade side of the tire resulted in another 1psi increase. At the same time the sun side temperature had risen another 10°F.

[oil pan 4]

Its looking like with the 50/50 CO2/R-404a mixture I am getting almost a 1psi change for every 10°F in temperature change.

I did a test like this on tires if purged and filled my self with 95% nitrogen back in 2006 and saw something like a 1.5 psi change for every 20°F change.

So the CO2/R-404a mixture only changes pressure with temperature slightly more than nitrogen. Nitrogen according to some people doesn't change pressure as it heats up.

http://ecomodder.com/forum/showthrea...tml#post255838

[oil pan 4]

Since immediate catastrophic failure has been ruled out it may be time to start limited on road testing, where 1 tire is filled with the mystery gas and the other 3 regular air.
So far my test tires have been with 2 brand new yokohama 30 inch load range C highway tires, that I purged and filled with CO2 and then took one tire forward with the R-404a test. These tires have been on rims and filled with air for a few months before I started messing with their inflation media.

I would also like to know whats going to happen this winter to these tires. Unfortunately I do not have a time machine. But a refrigerator and small trailer tire small enough to fit in said refrigerator should work in place of a time machine.

To be environmental friendly, save the O-zone (*cough* BS *cough*) and be cheap I have set aside an old empty R-134a tank that I can pump down to a vacuum and recover my tire gas. Soon I will have a compressor I can use to pull tire gas out of a tire and force in to a bottle. Then I have more tanks I can store gas in once the compressor is up and running, I dont think these other tanks will survive pulling a vacuum inside them.

The helium biasply trailer tire test will be soon. This test will just be to see how fast it leaks out.

[CapriRacer]

Originally Posted by oil pan 4

Its looking like with the 50/50 CO2/R-404a mixture I am getting almost a 1psi change for every 10°F in temperature change.

I did a test like this on tires if purged and filled my self with 95% nitrogen back in 2006 and saw something like a 1.5 psi change for every 20°F change.

So the CO2/R-404a mixture only changes pressure with temperature slightly more than nitrogen. Nitrogen according to some people doesn't change pressure as it heats up.

http://ecomodder.com/forum/showthrea...tml#post255838

Yes, some folks believe that old wive's tale.

But I disagree about the gases behaving differently.

The Ideal Gas Law predicts a 12°F change for every psi change, and 18°F for 1 1/2 psi. Looks like good correlation there for the data you are getting regardless of the gas. (Keeping in mind you are only able to measure the pressure to 1/2 a psi.)

[oil pan 4]

I believe you are correct.
The Nitrogen tire testing was more controlled.
The gas mix tire was heated by the sun and aluminum reflector.
My difference between the N2 tire test and the gas mix test was about a half PSI difference between the 2, that difference was likely caused by even heating of the N2 tire versus the uneven heating of the gas mix tire.
The gas mix test scope was to heat the tire up as much as possible from the base line to see if there were any wild pressure swings.

I thought there would be a much wider pressure swing with the R-404a mixture, because of the way refigerants act in a refrigeration system.

[bryn]

[QUOTE=oil pan 4;430103]
My difference between the N2 tire test and the gas mix test was about a half PSI difference between the 2, that difference was likely caused by even heating of the N2 tire versus the uneven heating of the gas mix tire.

you have a pressure gauge accurate to 0.5 psi and you are using a recorded difference of 0.5 psi as significant data?

so... um... well good luck with the research.