Why lose unused tires more air?

[Mono]

I believe I have seen this over and over again with bicycle and EUC tires: when I do not ride, it takes a few weeks or maybe 2 months and the tire is pretty much flat. When I do ride however, I may not do any refill for months and barely notice any air loss. It is easy to find an explanation, but I have no idea whether my explanation is correct.

What puzzles me even more: I fail to google any well-sourced explanation or barely any discussion of this anywhere else. Does anyone know this effect and knows evidence for its explanation?

Edited December 26, 2019 by Mono

[EUC Custom Power-Pads]

Are we talking about tyres and inner tubes filled with slime or similar? 

[Mono]

No, I can't say for slimed tires or for motorcycle or tubeless tires.

Edited December 27, 2019 by Mono

[LanghamP]

I've experienced the opposite on all my vehicles, and the very high 120 psi bicycle tires are the worst. That is, the tires will lose pressure after almost every ride, but can sit for almost a week without repressurizing.

Are you taking pressure readings after the ride? Tires gain 10-20 psi merely from getting warm.

A final possiblity, which I've only experienced with patched tires, is a poor patch job (guilty) gets better when the tire is used, that is, the increased pressure from usage seals the patch better than not using the tire.

[RockyTop]

This is a little off subject but interesting. ( Maybe) I had two open top 55 gallon drums in a construction yard. One had  about ten 1/2 inch holes in the bottom so that it could be used for storing scaffold pins without collecting water. The other was used to store water for a cement mixer. After sitting five years the one with holes clogged and filled with water. The other leaked and would not hold water.    Why!?

 

Edited December 28, 2019 by RockyTop

[LanghamP]

I wonder if filling tires with a large molecule gas would reduce air leakage.

[null]

in my experience slime (equivalent) have stopped (or strongly slowed down) leakage.

[Aneta]

6 hours ago, LanghamP said:

I wonder if filling tires with a large molecule gas would reduce air leakage.

That made me google the largest molecule (https://www.newscientist.com/article/dn19931-tree-like-giant-is-largest-molecule-ever-made/) out of curiosity, but then curiosity asked: what if we fill the tube entirely with liquid? Maybe, even Slime, not just water. (will be bloody expensive, though, to completely fill 18"x3" tire with Slime) Yes, the tire will become heavy, and there will be viscosity losses on ac/deceleration, but how would it feel to ride on liquid? An interesting experiment to do with an old tube.

[Denny Paul]

10 hours ago, LanghamP said:

I wonder if filling tires with a large molecule gas would reduce air leakage.

i want to say that this isn’t how it works, but I can’t why say for certainty. My guess is that the size difference of any gas at normal temperatures is insignificant to the size of the air leak sites of the tire. Sort of like if you were deciding between putting either baby powder or beach sand in a funnel; either way it’s coming out. 

3 hours ago, Aneta said:

what if we fill the tube entirely with liquid?

Main drawback is that water/liquid doesn’t compress much at all, and that the ability of air to compress well is what gives tires their suspension-y cushy feel by allowing the tire to flex as the situation demands. 
 

So with a water filled tire, I imagine you’d get either a waterbed feeling that feels unresponsive with water sloshing around in the tire. Or if you pressurized the water instead, it would begin to act nearly the same as a solid rubber tire.

[EUC Custom Power-Pads]

3 hours ago, Aneta said:

That made me google the largest molecule (https://www.newscientist.com/article/dn19931-tree-like-giant-is-largest-molecule-ever-made/) out of curiosity, but then curiosity asked: what if we fill the tube entirely with liquid? Maybe, even Slime, not just water. (will be bloody expensive, though, to completely fill 18"x3" tire with Slime) Yes, the tire will become heavy, and there will be viscosity losses on ac/deceleration, but how would it feel to ride on liquid? An interesting experiment to do with an old tube.

I would be very pleased if you would try out this experiment in detail under all conditions for at least 1 year and only get back to us when exact results of the study are available. 

[Mono]

OK, I found some related info on why CO2 escapes a tire much more rapidly than air. The reason seems to be that CO2 is better soluble in rubber 

http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html
https://bicycles.stackexchange.com/questions/731/is-there-a-difference-in-having-tires-filled-with-co₂-vs-air

It looks like solution and diffusion are the relevant mechanisms to look at.

That gives raise to a possible answer to the original question: rubber movements push molecules solved in the rubber back into the tube air.

Edited December 29, 2019 by Mono