Originally Posted by FBinNY

You don't need complex physics. Pressures simply add (in an application like this). So inflate the tire from empty or nearly empty with a CO2 cartridge and note the final pressure. Let's say you get 60psi on a tire where you need 95psi, or are 35psi short. Then you want to pre-pump to 35psi, and use the cartridge to top off at 95psi.

Of course this assumes same size cartridge and tire, but once you've dialed it in you can rely on it.