worth mentioning that whilst rim measurements are critical (errors in them always generate errors in spoke length) small errors in hub measurements are not so critical, especially if you are building with a tangent or near-tangent spoking pattern.
So, taking a 36x3 622 wheel as a starting point, the following all cause an error of 1.0mm in the spoke length;
- an error of 2mm in ERD
- an error of 10mm in the spacing of the flanges from the wheel centreline
- an error of ~4.5mm in the flange diameter
[By contrast if the wheel is built radially then the flange diameter is just as sensitive as the rim diameter, and a full tangent build (eg 32x4) builds with the same length spokes almost regardless of the hub flange diameter.]
Anyway for a typical x3 build onto a 32 or 36h hub you can measure the hub in a fairly slapdash fashion and it really won't make that much difference to the end result. By contrast quite a small error in ERD will always result in a spoke length error.
However I am in the habit of measuring everything as well as I can do despite this; sod's law says that all the errors will add up in one direction (rather than cancel out) and then you will then round the spoke length in the wrong direction, giving a poor end result. However if you measure everything carefully, you can normally get the spoke ends to finish mid-slot like they should do.
BTW if you find an error in the database for any online spoke calculator, please report it to the admin of the site; the databases are only as good as the (user-generated) data that is entered into them.
cheers
