I'll venture that any pinch leak you might have caused would have shown up in a bubble test. Also it's highly unlikely that you would have cause such matched leaks in two tubes. So you're likely looking at the normal bleed process, rather than a leak.
All tubes bleed air because of porosity in the material, the rate of bled depends on a variety of factors.
1- ratio of surface area to volume, with narrower tires therefore bleeding faster than fatter ones.
2- initial pressure with higher pressure tires bleeding faster because the air it trying harder to escape.
3- the porosity of the tube's wall. This varies with the material and thickness, with butyl (black) rubber holding air better than natural or latex rubber.
Narrow high performance tires and tubes do worse on all three scores, having high surface/volume ratios, high starting pressure, and thinner walls, or in some cases being latex vs. butyl.
You've heard of win/win situations? When it comes to holding air narrow HP tires and tubes are lose/lose & lose. 1/3rd of the pressure overnight seems to be at the high end of the range, but 1/4 overnight isn't rare at all.
If you stay with HP tires, buy a good floor pump, and be ready to top off daily.
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FB
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Last edited by FBinNY; 11-24-13 at 04:13 PM.