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I'll be building a pair of wheels soon and I always get the feeling I've got the calculations wrong and will order the wrong spokes, so could someone check all this for me please?
[url= http://www.sp-dynamo.com/8-series-pic/PD-8-QR-01.pdf ]SP PD8 dynamo front hub[/url]
Left diameter 58mm
Right diameter 52mm
Offset 23.4mm both sides
Crossing 3
[url= http://www.rohloff.de/en/technology/speedhub/technics/index.html ]Rohloff rear hub[/url]
Diameter 100mm both sides
Offset 50mm both sides
Crossing 2
[url= http://www.velocityusa.com/product/rims/dually-622 ]Velocity Dually rims[/url]
604mm ERD
Using www.wheelpro.co.uk/spokecalc/ I make that;
Front left = 291.6
Front right = 292.5
Rear both = 273.7
So that'll be 292 & 274 then.
Have I got that right?
Does it make any difference that the Dually holes are offset from the centre line a bit?
I've never been brave enough to calculate this myself so I'm certainly not brave enough to check yours for you. However, for the dually, the term [b]effective[/b] rim diameter would suggest that any offset etc is taken into account in the quoted figure, precisely so it can be used to calculate correct spoke lengths. That's if its not a total misnomer...
The calculator will need to consider the number of spokes, too. Assuming it's 32 on each wheel, it looks close to being 290mm for ALL your required spokes (if you went 3-cross on the rear) which might save you some money... I always buy shorter than the calcs show (by 1 or 2mm) so I don't run out of thread when tensioning.