Originally Posted by
trace
There goes my top theory...
I usually inspect the inside of the tire after getting a flat, but I didn't in any of these cases since the tubes seemed to still hold air perfectly well. So I figured it was not a sharp object, but maybe some kind of intermittent valve leak, or, you know, gremlins.
But could just be a very small sharp object.
I have another tube lying around from a past mystery flat, which seems to hold air, but I'm going to check it underwater and see if I can find the hole. I have had this happen both front and rear, so it's not something like a sharp spot on the rim.
I'm gonna get a low pressure gauge to see if I'm heading into pinch-flat pressures, and also try the talcum powder thing. Never used talcum powder before, but it seems reasonable that with a fat tube -- at low pressures and with so much more surface area than a regular tube -- that friction inside the tire could be an issue.
Pump that past mystery flat tube up, huge like a life preserver, and let it hang. It will tell you in a week or so if it has a hole. As you saw, slow leaks can even be hard to spot in water.