As to measuring ERD I strongly suggest doing it around the rim at least at 3 points. Both to average out any rim issues and your measuring skills.


A different rim of the same published profile might also have a thicker wall at the spoke hole section. One rim might have, or not, eyelets depending on the version of the same extrusion (OEM rims are often a cheaper version of the same rim blank that the up scale "over the counter" uses. Just delete the eyelets, thicken the spoke bed, pin instead of weld the seam).


Lastly before you take apart the wheel look at where in the nipple the spoke end is. Getting the spoke end to line up in the nipple's head is generally considered best, not all wheels have achieved this.


As always, one good measurement is worth a thousand assumptions. Andy.