How to determine proper spoke length

[Joe Nunn]

Hi all...
I'm planning to lace a client's front hub to a new rim that is different from the original.
I'd planned to input the hub and rim dimensions into a spoke calculator, but, because of the spacing of the spoke holes in the hub flanges, don't think I'd get an accurate result. There are nine groups of four holes clustered together rather than 36 evenly spaced holes, as the calculators assume.
Any ideas on how to determine the proper length by comparing the erd's of the original and new rims and extrapolating from the wheel's original spoke length?
Any suggestions would be appreciated.
Joe

[Bikemad]

Hi Joe andto the forum.

If the motor has the offset pairs of spoke holes it is probably a Magic Pie, in which case, you simply need to use a spoke calculator that caters for the offset paired holes in the hub, like the ebike.ca spoke calculator.
As the Magic Pie II, III, 4 and 5 hubs with laced rims all use the same paired hole measurements, you will need to select the Magic Pie "3" hub option with the "0" Cross Pattern. I suggest that you have the spokes fitted with their elbows on the outside of the flanges for better support, and also to provide greater lateral strength for the wheel rim as shown here:



If your exact rim is not listed in the dropdown options, you will have to select "Custom Rim" and then manually enter your rim's ERD measurement:



I prefer the spokes to be fitted on the outside of the flanges with the heads on the inside as shown here:



Fitting the elbows on the outside will provide better lateral strength for the rim, and will also help to alleviate flexing and fatigue of the unsupported spoke elbows at the flange attachment.

Check out this post for more details.

I recommend using Sapim 13/14g stainless steel single butted strong spokes. They are very strong (1400N/mm²) and rated for 1.6 million revolutions:



Alan
 

[Joe Nunn]

That's very helpful. Thanks Alan