Old spokes: nds:294mm / ds:295mm
Old rim ERD: 597mm
New rim ERD: 605mm
Measured spoke length on prowheelbuilder calc:
Old rim: 287/288
New rim: 291/292
With this small ERD change, adding the missing 8mm will be fine, but I would rather know how to measure those things accurately in the future. Does Sheldon have anything on that?
by ChickenTendies0
2 Comments
I’ve never done it but I was always curious to try: [https://spokecalc.io/exotic-wheelbuilding.php](https://spokecalc.io/exotic-wheelbuilding.php)
I’ve tried–and failed–to come up with a quick and dirty way of calculating spoke lengths for such hubs. Wheels built with these are predicated on dedicated lacing patterns and spoke lengths so the builder is locked in. The relationship between ERD and spoke length deltas isn’t linear so you’ll be guesstimating when swapping in different rims. The rare times I actually want to use such hubs I resort to calculated guessing rounded out with trial and error.
You could try punching in all relevant values of the old wheel into Jobst Brandt’s spoke length formula (or online equivalent) then tweaking the spoke crosses and hub’s spoke hole count (you’ll have to measure flange offset and PCD’s), until it spits out the correct length for the old build.
Then, keeping every other value the constant, update the formula with the new rim’s ERD to see what new spoke length you get.
[PDF of The Bicycle Wheel by Jobst Brandt](https://poehali.net/attach/Bicycle_Wheel_-_Jobst_Brandt.pdf)