Homeless in Vancouver: I'd like to figure this out—but no pressure
The last two spells of cold weather weren’t very demanding or difficult to cope with, but they did have their curious moments.
For instance, take the micro-leak I had in in one of my bicycle tires—please (Ba-dum!).
At 9° C—this morning’s temperature—I could expect the tire to leak out in about seven hours. But at -6° C it didn’t appreciably leak at all. Even at 0° C it only lost about 10 pounds of pressure in about three days.
I realize there is an interrelationship between air pressure, temperature and density; there’s a higher density of air at the bottom of the gravity well, and higher temperatures mean more energetic molecular movement, which means higher air pressure.
So I understand that as the temperature drops so does tire pressure. But what I clearly don’t understand is the mechanics of the differential between the air temperature and pressure in a tire versus the ambient outside air.
If I have a slow-leaking tire—fully inflated—in subzero weather, I would think the pressure and temperature is higher inside the tire than outside. I would expect the tire to leak faster to equalize with the outside lower pressure until an equilibrium is achieved.
I must have everything backward; if the ambient outside air pressure was higher than inside the tire then I would not expect the tire to leak, but I don’t see how that could be in minus-degree weather.
Unless the point is that all air pressure is lower in subzero temperatures and less energy means less leaking, period.
Ah well, another thing I don’t understand. So deflating, ego-wise.