its the correct way to measure.,,, your not wrong there,,,,,, but assuming it has a Q18 pipe??? i have to say you will not find the correct center... you physically have to cut one apart to see what i mean....... the front cone is made into a long outer sleeve,,, the rear cone is then slid into that sleeve till the cone butts up against the center band.... in other words there is no means of measuring accurately cause the center band and rear cone start can not be seen.....
if its a different pipe,,,, then you are measuring correctly........ sorry for any confusion,, this strictly applies to the super tigre Q18 pipe that comes with the duece...
alden