Originally Posted by khuon
Let's not forget highschool chemistry...
PV = nRT
The amount of pressure in the end for which you can achieve with a certain size cartridge will be a function of the size of your tyres and the size of the cartridge. That is to say that if a 12g cartridge is guaranteed to inflate a 700x20C tyre to 100PSI and you manually inflate with a pump to 30PSI before using the cartridge, you will not necessarily get to 130PSI at the end. Once pressure equalises at both ends then you're done.
Didn't you mean to say "Let's not forget highschool physics?"