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Discussion Starter #1
I've been riding my tubeless setup all summer long in the 10-14 psi range (even lower a few times) and have never had a problem with flats.
Yesterday I hit the snow for the first time and both tires went flat within 45 minutes.:madman:
The only explanation I can think of is that I set my pressures at 6 psi front and rear in a 40* garage, then the snow and 20* air caused the psi to drop too much and let the side walls burp? The bead never came off, they just went flat.
Anyone else experience this before?
I also found out that CO2 inflators are useless at 20* temps.
 

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What setup are you running? Do your rims have holes drilled in them and if so how did you thicken up center. I know when I did the split tubes method on my fat bike I had the PSI low it was not sealing properly and when I dropped to anything really low and pushed on the side wall I could see sealant finding its way out.
 

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I'm running marge lites with floater rear and knard front. Duct taped the centers, put the sealant in and aired them up, nothing else. Like I said, I have ridden down to 6 psi in summer without any problems. I think maybe the cold temps dropped the psi lower than I thought it was.
 

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Well i think you might have answered your own question then =P Id say air it up to a bit over 6PSI on a day that is around similar temp and see what happens. My tires have dropped and gained PSI from temperatures as well but I am just running tubes with sealant in them. If it doesnt burp on you then problem solved.

I asked about the center rims because my friend had problems using tape over the holes and fixed it using the foam trick and gorilla tape over it. His would hold but any real moisture would cause the tape to fail and he would flat. Figured if packed snow or wet slush was in the center rim over the holes it could do the same.
 

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since 4/10/2009
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PV=nRT

Yes, the pressure will drop when the air in your tires get cold. Either start high or inflate at the trailhead after the bike is cold (if you use a rack outside the car).

Also, your tubeless method may not hold the bead on at just a couple psi so it very well may be burping at some point.
 

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I've been riding my tubeless setup all summer long in the 10-14 psi range (even lower a few times) and have never had a problem with flats.
Yesterday I hit the snow for the first time and both tires went flat within 45 minutes.:madman:
The only explanation I can think of is that I set my pressures at 6 psi front and rear in a 40* garage, then the snow and 20* air caused the psi to drop too much and let the side walls burp? The bead never came off, they just went flat.
Anyone else experience this before?
I also found out that CO2 inflators are useless at 20* temps.
You did answer your own question. Air pressure will drop at least 1psi when going out in the cold. Also, there are many tubeless setups that will work when the pressure is higher but will fail when the pressures are low.
 

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This happened to me. I was running around 7 PSI when the temp was around 20 deg. The next time the temp was -5 and the rear went flat. I put more sealant in and inflated to 11 PSI at 38 deg in the mud room and took another ride with the temp around -10. Pressures had dropped approx 2 PSI. My set up is Weinmann HL80, split tube, On One Floaters with Stan's.
 

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Run nitrogen? Temperates have little impact

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You failed high school chemistry didn't you? All gases become more dense as they cool. Eventually they will all become liquid and even solid if you go cold enough. ALL gases. The only differences are the points at which each gas changes states. Besides that, air is still ~78% nitrogen.
 

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You failed high school chemistry didn't you? All gases become more dense as they cool. Eventually they will all become liquid and even solid if you go cold enough. ALL gases. The only differences are the points at which each gas changes states. Besides that, air is still ~78% nitrogen.
No need to be a wank about it you tosser...I know that nitrogen can absorb heat better then air and i use nitrogen in my motorbike tyres and car track tyres. Not sure if it was the same for bike tyres but i guess the temperature difference isnt as big

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Btw oxygen has a higher defusion rate then nitrogen, nitrogen will disspiate at a much slower rate then oxygen. Just had a chem eng (sitting next to me confirm) so yes running nitrogen will still lose psi but not as much as oxygen/co2

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To expand on NateHawk's comments for those who are really nerdy:

If you assume that the volume of your tire is constant from warm to cold and that no air is escaping, the relationship between temperature and pressure is:

Cold Pressure/Cold Temperature = Warm Pressure/Warm Temperature

Pressures and temperatures need to be measured in absolute terms, so pressure = gage pressure + 14.7 psi (approximate atmospheric pressure) and temperature = degrees F + 459.67 (0 degrees F = 459.67 degrees above absolute zero).

Hotrozz, for your scenario (6 psi @ 40 degrees F), the pressure at 20 degrees F should be roughly:
(6 psi gage + 14.7 psi atmospheric)/(459.67 + 40 degrees)*(459.67 + 20 degrees) = 19.9 psi absolute - 14.7 psi atmospheric = 5.2 psi gage.

radnur22, for your scenario (11 psi @ 38 degrees F), the pressure at -10 degrees F should be roughly:
(11 psi gage + 14.7 psi atmospheric)/(459.67 + 38 degrees)*(459.67 + -10 degrees) = 23.2 psi absolute - 14.7 psi atmospheric = 8.5 psi gage.

By the sounds of it, your tires are losing air in addition to the drop in pressure caused by temperature. Not sure why, but my guess is that it has something to do with aluminum and rubber shrinking ever so slightly in the cold.
 

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Btw oxygen has a higher defusion rate then nitrogen, nitrogen will disspiate at a much slower rate then oxygen.
For us dummies, Nitrogen is thicker than Oxygen, and therefore will not leak through the same size holes at the same rate as Oxygen.

OP, when is the last time you filled up your sealant? Dump a few oz's in your tires and see if that helps.
 

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I had this happen last weekend in the cold...

I've had my new wheels & tires tubeless for a few months, never had a problem. Aired them up a bit (~7psi) at the start of the ride. After a few miles in the rough stuff, the rear only began leaking very very slowly sealant around the beads. No bubbles really at all. Every time I would stop, I'd get a little drip of Stan's leaking down the tire at the bottom.

Never really lost air at all, but it bothered me that sealant was slowly leaking. Came home, put it in the house and it stopped.
 

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Btw oxygen has a higher defusion rate then nitrogen, nitrogen will disspiate at a much slower rate then oxygen. Just had a chem eng (sitting next to me confirm) so yes running nitrogen will still lose psi but not as much as oxygen/co2

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You really must have failed high school chem. Sure, you can get intelligent answers to your questions from a chemical engineer, but you have to ask the right questions to begin with. You really think the OP is actually LOSING appreciable air from his tires within 45 minutes? Not likely. For our purposes here, we can assume that the actual amount of gas in his tires does not change (at least at first). Technically speaking, yes it does some small amount, but in 45min, that amount is going to be negligible.

What is happening here is a temperature change. This is the largest change to the conditions that's occurring within the 45 minute timeframe (drop of 20deg F from garage to outdoor temps). The air in his tires becomes more dense as it gets colder. It does not matter if it's ambient air, or pure nitrogen, or pure hydrogen, or pure sulfur hexafluoride. All gases become more dense at colder temps.

The OP is talking about pretty low pressures to begin with, on rims and tires that are not tubeless ready. If the tires are going COMPLETELY flat at some point, it is quite likely that he is dropping below the threshhold at which the air in his tires can keep the bead sealed against the rim. Burp. Air goes bye-bye. This exact same process would happen if he put pure nitrogen in his tires, except he'd have to keep a tank of Nitrogen in the garage.
 
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