I'm about to build my 7th wheel and still learning. I bought a nice shiny Pacenti rim and the sticker reads "ERD 611." Because I'm still trying new things, I measured it, several times, in several locations, and I get an ERD of 615.
I cut 2 spokes to 200 mm and screwed a nipple on each one until the spoke was flush to the top of the nipple. I put 'em in opposite holes on the rim and carefully measured the space between them. When I total the numbers, my measurements are always higher than the published ERD.
If I calculate spoke length with the published numbers the spokes would probably reach to the bottom of the screw slot.... Why would I waste the last remaining bit of threads for such a thing?
Am I missing something simple?