Originally Posted by
alcjphil
Inner tubes are not responsible for maintaining high pressure. They are confined in place by the rim and tire. In fact, the least reliable inner tubes I have ever used were quite expensive. They were lightweight Scwalbe inner tubes that I bought when the distributor I worked for at the time had lost Scwalbe as a client
The tire and rim are responsible for
containing the pressure. The inner tube is responsible for
maintaining the pressure. It’s the bladder that holds the pressure in place. If the tire were tubeless, the tire takes over that function.
Fick’s Law is what describes how gas diffuses across a membrane. It says
Fick's First Law states that 'the rate of "diffusion (e.g. of a vapour) is proportional to the surface area and the concentration difference, it is inversely proportional to the thickness of the membrane".
For bicycle tubes, that means that the thicker the tube, the slower the diffusion. Lightweight tubes are, by design, thinner so they decrease in pressure more rapidly. Higher pressures will also lose pressure faster than lower pressure systems.