Spoke length for Ultegra 6600 hubs to Mavic Open Pro rims
Dear wheelbuilding pros,
I'm ready to order spokes. I'm 3x lacing 36H Shimano Ultegra 6600 hubs to Mavic Open Pro rims using DT Competition spokes (2.0/1.8/2.0) and DT 12mm brass nipples. There doesn't seem to be exact agreement about the ERD of these Mavic rims. What spoke lengths should I order? I don't mind ordering three lengths of spokes if that's best.
DT Swiss calculator (uses 604mm ERD):
Front left+right: 293.8mm
Rear left: 292.7mm
Rear right: 290.9mm
Spocalc spreadsheet (uses 605mm ERD):
Front left+right: 294.3mm
Rear left: 293.2mm
Rear right: 291.4mm
Mavic dealer calculator (does not disclose ERD but I infer a value of ~604.5):
Front left+right: 294.2mm
Rear left: 292.9mm
Rear right: 291.1mm
So I'm tentatively thinking:
Front left+right: 293mm?
Rear left: 292mm?
Rear right: 290mm?
(Inputs from Shimano's site: front hub spoke hole circle = 38mm; front hub centre to flanges = 35.8mm; rear hub spoke hole circle = 45mm; rear hub centre to left flange = 38.4mm; rear hub centre to right flange = 20.8mm. Inputs from http://lenni.info/edd:
front hub spoke hole diameter = 2.6mm; rear hub spoke hole diameter = 2.5mm. I don't trust the exactness of these spoke hole diameter measurements but they impact spoke length very little. The Mavic calculator does not factor in spoke hole diameter.)