Originally I was running 29 psi of air. When the tires were fully heated up I would reach 37 psi. This is a heated difference of 8 psi when the outside temperature is about 90.

Yesterday I bought a CO2 inflator from a bicycle shop and a bunch of airgun C02 cartridges from Walmart. The Cartridges are about 12 bucks for 25 and it takes about 12-13 to fill a tire and I used 1 to purge the air out of the tire. I over filled each tire to about 33 to 34 psi and let out CO2 until my Accutire digital guage read 31 psi. This was done after the car had set overnight to make sure I was getting an accurate cold reading. After driving the car about 20 yards the tire pressure monitors all read 31 psi, once again proving their accuracy. The other thing that I noticed is that the pressure from tire to tire increased very consistently from each other. I would see an increase on the monitors within seconds of each other.


I then headed for the freeway to heat them up. The max pressure reached 36 psi on all the tires. This is a difference of 5 psi from cold to hot.


Was it worth it? I don’t know. If you are setting off your inflation alarm 3 psi might be worth it. Since I am anal about my car and watch these kinds of things closely it was a fun experiment for me. Now, I’ll carry the inflator and a hand full of cartridges in the trunk, that seems like a good idea to me.

You could probably go to an industrial supply that provides compressed gas and get a fairly large amount for much less. Thanks for the info. This is certainly a benefit to tire longevity. Verify scientific.

http://www.powertank.com/


I KNEW I could fuse my two automotive fetishes..... my V and my Jeep!!!! My wife will want to kill me!!!!

We use these to air up tires and some use them to actuate gas powered differential lockers. I personally perfer mechanical lockers (Detroits) but the Powertank will air up a 35" tire from 0 to 30 psi in a few minutes.

I've got a portable air tank that I fill up with my compressor. There is a paint ball place near me. I think I'll see if they can fill it up with CO2 for me just to have on hand.

<semi thread-hijack in-progress...sorry>

SilverBullet:

Glad to see another V/Jeep junkie on the boards!

I have a YJ set up for trails and a WJ Overland that's my daily driver. The Wrangler was supposed to be the only vehicle I get to mod, but you KNOW how that goes...

Why CO2 over nitrogen?

Could not find a ready source of Nitrogen.

slow35th,

Danger, Will Robinson!
I have a Powertank. The static pressure in the tank is about 800psi! Your air tank would typically be 125-150psi.
I wouldn't use a tank rated for less than 1500psi and preferably 3000psi!

Yes, I found that out yesterday. I didn't realize the Paintball boys were running pressures that high. I'll just stick with the 12 gram cartridges for now.

Wow, never thought i'd get to do this rant on the v forums ... I played paintball at a semi-pro level for several years. Here is the breakdown of paintball products that could be used for tire filling...

co2 -- this is kept liquid in the tanks by pressure/temperature and without an anti-siphon system or remote hose (the coiled hose) to your adapter for your car, you will eventually dump liquid into the tire and it will over-pressurize as that liquid expands with heat. Most paintball co2 cylinders are under 20oz and are ~2500 psi rated. Some go higher but most are around that range. Average output from these tanks is 800-900psi.

hpa -- high pressure air, simple fills from scuba stations or shops. I have 3 80cf scuba tanks at 3k psi, with the paintball HPA tanks running ~68ci of 3000 psi fills. These smaller tanks with a remote make a great way to fill a tire as long as you do it slowly and in a controlled manner. Almost all of these have an adjustable regulator to control output pressures/volumes. If there is no attached regulator, it is built in spring-style into the ball-valve.

nitrogen -- least common and hardest to get fills for. Scuba shops sometimes carry pure nitrogen and make their own mixes, but you often have to go to a air supplier (air liquide, etc). Same tanks as HPA.

co2 is the best pressure/price unless you own your own scubas for air storage/fills. However, it is very volatile and should be handled with caution, as just fully-opening a valve on a paintball tank of co2 will often end up just dumping liquid and blowing the burst-disk inside the tank ball-valve. I have one of those little co2 air fillers for each of our motorcycles -- you can buy cheap 12-grams of co2 at your local paintball shop (usually). I can often get ~100 for $25, which is 2x cheaper than wal-mart.

What's best? Got me... My father does construction supply, so I'm just getting a gas compressor for the garage to handle my fills from now on.

-Tim

Hmm. I use those CO2 cartridges to get home after a flat on my bicycle. First thing I do when I get home is dump the CO2 and replace it with real air from a pump - b/c if I don't, it will be flat in the morning anyway. Bicycle tires (at least mine) use an inner tube that holds regular air, but lets CO2 escape. I don't know if a car tire will act the same, but I would keep an eye on your cold pressure.

I have 18 credits of useless chemistry. The only reason I can think of a tire releasing the CO2 would be due to a smaller molecule size. Simply put a molecule of CO2 would be larger than a molecule of O2. Although the air in a tire is not pure O2. I'm perplexed on this one. I shall consult the oracle.

Don't want to rain on anyone's parade...but... check out the attached link to gas data on CO2 from a very reliable supplier - Air Liquide. The material compatability chart says that CO2 should not be in prolonged contact with butyl or nitrile rubber due to "significant swelling and loss of mass by extraction or chemical reaction". CO2 is also corrosive to carbon steel in the presence of moisture - likely due to formation of carboxylic acid. Although the wheels are no problem since they are alloy I don't know if this is a concern for the TPS.

Also says that CO2 will freely permeate through silicon compounds - maybe bicycle inner tubes are made of silicon rubber.

http://www.airliquide.com/en/business/products/gases/gasdata/index.asp?Formula=&GasID=26&UNNumber=&EquivGasID=26&PressionBox=19.7&btnPression=Calculate&VolLiquideBox=&MasseLiquideBox=&VolGasBox=&MasseGasBox=&btnMSDS=0&MSDSLanguageBox=0&RD20=29&RD9=8&RD6=64&RD4=2&RD3=22&RD8=27&RD2=20&RD18=41&RD7=18&RD13=71&RD16=35&RD12=31&RD19=34&RD24=62&RD25=77&RD26=78&RD28=81&RD29=82#GeneralData

Yep, after about a week and a half I have lost about 3 psi, so I'm going to remove it tonight.