Originally Posted by
hamster
So what you're saying is that I want my spokes to extend all the way to the end of the nipple flange, which is 2 mm past the inner wall of the rim?
Remember, that as currently used ERD, refers to the circle formed by the end of the spokes, not the diameter of the rim in any sense of the word.
Years ago (before Jobst Brandt wrote the book) wheel builders used to refer to the rim diameter meaning the diameter where the nipples sat. I don't remember if we ever used the phrase
effective rim diameter since most of us didn't speak bureautocratese, but in any case JB defined it as the circle at the ends of the spokes.
That means that as used by most Americans the ERD is bigger than the nipple seat diameter by the amount of engagement in the head of the nipple (doubled). Unfortunately, many Europeans have been doing this a long time (Before JB) and never read the book, so to them the ERD is measured at the rim, which is what leads to the confusion. I measure the same way and call it the rim diameter as I always did, but when speaking to post JB builders call it the nipple seat diameter so as not to add to the confusion.
Figuring typical 3mm engagement in the head, the ERD in 5-6mm greater than the RD (or NSD).
The key in all this is to remember that most calculators will bring spokes out to whatever ERD value you enter (or very close) so if, like me) you measure rims, you have to either add 5-6mm before calculating, or add 3mm to the result.