Originally Posted by
Drew Eckhardt
I wouldn't use a calculator with a database since there can be a 4mm difference between published numbers (there isn't a standard for aiming for the slot or nipple end) which is the difference between a perfect wheel and one that doesn't build because you run out of thread or break nipples.
It depends on how the actual rims you have measure (at at least two points) when you thread a pair of spokes into the nipples you plan on using to the slots and add twice that spoke length to the measurement across the nipples with your dial calipers.
It also depends on what spokes you're using - 2.0/1.5 spokes stretch nearly 1mm on the drive side and half that on the non-drive side.
I didn't know that about the butted spokes, and I hadn't thought about the standard, so they're certainly two interesting points to consider.
I measure the same way you do (I even glue in the spokes so they don't move) and the ERD on the lenni calculator has always been the same as my measurement in the past. I haven't measured the Excellights myself, but a few online sources have the ERD as the same (600). The guy in the shop has a book with rim ERDs and the correct spoke/nipple combos and he still insisted I'd be ok ... but now I'm more unsure than ever!
I guess I could try to roll the online dice again ...