Originally Posted by
Rowan
This is far more normal than putting goop into a tyre. Like, it's been that way since the tyre was invented.
I believe it has to do with the size of gas molecules in the air, and the smaller molecules find a way of permeating through the rubber inner tube. I think people who use CO2 to inflate their tubes, have greater issues with deflation over a shorter period than those who use normal air.
Car tyres don't have the same issue to the same extent, mainly because... well, have you seen how thick a car tyre is?
This is the theory behind using nitrogen to fill vehicle tires. Nitrogen is a relatively large molecule and thus, should escape more slowly through the rubber membrane. Marketers also claimed that it caused tires to run cooler. In the 1990s-2000s this was a popular service at places that sold tires, but you see it less often today.
I use a proprietary blend of 78% nitrogen, 21% oxygen and less than 1% carbon dioxide
. I still need to top off my tires every few days (not necessarily every ride). In a week I lose 10-15 psi, more from my road tires and less from my larger and lower-pressure touring tires.