Don't forget that the final inflation pressure a CO2 cartridge is inversely proportional the volume of the tire. Rather than worry about the volume, you can compare likely inflation pressures by comparing the squares of the diameters. For example, a tire 1.4 times wider will have double the volume, and fill to half the pressure.
This is why I suggested you start by establishing a base line for your specific tire by filling if from near empty.
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