Originally Posted by
oldbobcat
Here's a suggestion for measuring ERD accurately. Thread a nipple onto an old spoke and cut the spoke off 2-3 inches above the nipple. Now the nipple is your rim depth gauge and the clipped spoke is the handle. Insert the nipple into the spoke hole, with nipple washer if necessary, and mark where the nipple protrudes from the inside of the rim. Remove gauge and measure from the mark to the butt portion of the nipple. Add twice this measurement to the inside diameter of the rim for an accurate ERD.
Or - insert two spokes into opposite (spoke number divisible by 8) or almost opposite holes (not divisible by 8). Thread nipples onto the spokes. I thread the nipples down to just below the nipple top but above the screwdriver slot. Now, pull the spokes together and wrap a rubber band around the J-bends. Measure from inside of elbow of one spoke to the same on the other. (The same points you measure spoke length from. I bet Park or DT has a diagram spelling that out.) Now simply add the two spoke lengths and your measured distance. ERD. That simple. No cutting. Nothing wasted. I do this in two directions and take the average. Andy above uses three directions. (Rims may be a little egg shaped but pull easily to round.)
Advantage of this method is that it reflects where you want the spoke end to be in relation to the nipple top. (The spoke will stretch perhaps a mm depending on both tension and spoke diameter.) I want room on both sides of my target so with variations in spoke length, hub flanges, rim seats ... I do not run out of threads or have a spoke below the nipple head. Yes, I have run out of threads and simply forced the nipples another turn or so but mickey mouse and not doing the next person who needs to true the wheel any favors. Too short = nipple busters. And an excellent chance that nipple top will be lost forever inside that rim to bug someone for years if the rim does not have ferrules.
Oh, and the math is really easy!