Originally Posted by
tkramer
CO2 is not inert like nitrogen (it acidifies water and with water vapor). So, it reacts with other molecules in the tire/rim chamber surfaces, taking it out of the gas phase.
Any chemical actions won't be sufficient to account for the pressure drop.
The problem is that butyl is more
"porous" to both C02 and oxygen than it is to nitrogen. Note that I said porous only for lack of a better word. It's not pores in the physical sense and the size of molecules. It's more a chemical sort of thing, whereby some molecules are able to slip into and through a material while others can't.
So, you will see a faster pressure drop when using CO2 vs air, but IME it's not an earthshaking difference, and if the tire loses more than 20% or so pressure overnight, odds are you missed something or the new tube has a leak also.
It's extremely common to suffer flats in succession because the sharp that caused the first one was left in the tire, or because you pinched the new tube on installation. Don't blame the gas (whatever gas) for escaping, it only did so because there was a leak someplace.