Calculating spoke length with staggered spoke rim holes?

[bowlofsalad]

Hello,

I am working on fully assembling (choosing all the individual components, and putting them together) a bicycle wheel (non-ebike, mostly for practice) for the first time. The measurements I am working with are as follows, effective rim diameter is 392mm (mutant elektra rim), inner hub flange width is 52mm, and hub flange diameter is 60mm (shimano deore XT m756 hub). With these measurements I came up with 183.3 or so, so the plan with that was to use 184mm sapim race (14/15/14) spokes from danscomp.com (great price) and sapim polyax nipples all in a sexy black. I was about to call them up to place an order but I decided to triple check my work once more when I realized the spokes holes on the rim were offset from the center.

Both sides come up with 392mm, but I am still a little uncertain if I need to make any special accommodations in the calculations. One person has suggested to me to take the spoke hole offset in the rim (either 3mm or 5mm, depending on if I measure to the edge of the spoke hole or the center) and subtract that from the inner hub flange width. With this in mind, I come up with either 183 or 182.8 or so. If I am using 182.8 for the calculation, I could use 182mm spoke length, but being uncertain in all this I'd rather not guess with a difference of 2mm and the money spent on spokes. I could go with 183mm and be perfectly fine either way, but those spokes (dt swiss competition) cost well over twice as much and I still wouldn't be certain on what to do in situations of staggered spoke holes on rims (which I know is going to come up again for other wheels I have planned, ebike or otherwise). Maybe sapim race spokes come in odd lengths, but I haven't been able to find them.

Should I ignore the staggered rim holes in the calculations? If I should consider them, how should I measure the offset and how should I attribute that to the calculations? Thanks!

 

[Tench]

Justins spoke calculator has the ability to accommodate paired holes in its calculations.

Sorry, I misread your post, you should measure the distance between the 2 rows of holes in the rim and knock the same amount off the flange to flange measurement of the hub, or knock half the amount off the flange to centre line measurement depending on which figure the calculator asks for.

http://www.ebikes.ca/tools/spoke-calc.html

 

[cal3thousand]

Use ebikes.ca spoke tool and let us know how well it did for calculating the paired holes.

This might be interesting for conversion of some rims and some crazy/fun builds.

 

[bowlofsalad]

Justins spoke calculator has the ability to accommodate paired holes in its calculations.

Sorry, I misread your post, you should measure the distance between the 2 rows of holes in the rim and knock the same amount off the flange to flange measurement of the hub, or knock half the amount off the flange to centre line measurement depending on which figure the calculator asks for.

http://www.ebikes.ca/tools/spoke-calc.html

Thanks for the reply!

Measuring from the face of the rim that faces the hub or center of the rim, should I measure to the edge of the spoke hole or the center of the spoke hole? I either come up with 3mm (6mm total) or 5mm (10mm total).

The difference between the two measurements isn't that big of a deal here (but I really enjoy doing things with as much accuracy as I can), but I imagine in some cases this might matter a whole lot more.

 

[bowlofsalad]

After an obsessive and obscene amount of reading, question asking and searching I think that I feel that I can agree with what tench suggests. However, what gives me extremely high confidence within this whole idea is this calculator. http://www.kstoerz.com/freespoke/fullcalc

This calculator has two(maybe more like 4, but you can check them out yourself) excellent features that I don't seem to see else where. Individual spoke bed offset allows you to set the offset for each rim spoke hole, all the calculators I used that had anything like this always assumed that the spoke holes were still lined up. The other feature, which is brilliant, is the visualization created beneath the calculation, I am skeptical I would have felt really solid about my calculations without this visualization.

The only feature that is lacking from the spoke calculator is spoke angle. I can use other calculators for that, but it wouldn't be bad if that was also with this calculator. Anyway, I thought I'd share this information, it might help someone else in the future.