Which spoke length calculator?

Buk___ · Dec 3, 2017

I just got a new rim, measured the ERD and fed it into two different spoke length calculators:

Sapin.be site gives: 210.7 & 209.7

ebikes.ca site gives: 207.2 & 208.3

And I get different results. They each ask for a slightly different set of input data, but I've tried very hard to supply accurate info to both as measured directly from the hub and rim using the the best tools (laser ranger for the rim diameter; vernier gauge for the rim thickness flange offsets etc.); but the discrepancy between them seems a little too large to ignore.

Which would you use?

speedmd · Dec 3, 2017

Sapin is only to outside of flange and spoke nipple head interface of the rim. You will want the spokes to extend into the nipple heads which the ca calculator clearly does. Careful with the sapin length if you plan on running spokes from the inside of thick flanges and can not tolerate spoke protrusion if you add the spoke head dimension. It is not clear what adjustments are being done on the sapin numbers. I always err to the long side. Easy to roll a few threads if need be. Check your ca numbers against some others. http://www.prowheelbuilder.com/spokelengthcalculator

docw009 · Dec 3, 2017

Yes. I just did this for my Q128H using Grin and Sapim. ERD of 522mm. Sapim's online calculator said 202 and 203 mm Grin was 199 and 200mm.

In the past, when I used the Grin calculator, spokes were always too long and I needed to stack washers under the nipples or re-order. So I ordered 198 and 199 double butted Sapim.

If I had a spoke roller, I'd go longer too. I keep saying I don't need a roller, this is my last wheel, but I could have paid for half the cost of one by now.

Buk___ · Dec 3, 2017

speedmd said:
Sapin is only to outside of flange and spoke head interface of the rim.

Hm. Maybe I misinterpret you, but I don't think that can be right. Their "rim thickness" setting is a direct addition to the calculated length.

Also, as they are calculating the longer of the two measurements ...

Chalo · Dec 3, 2017

This is the calculator I use most:
https://leonard.io/edd
It's an online version of Damon Rinard's Spocalc spreadsheet.

I round up to the next longer size spoke.

Buk___ · Dec 3, 2017

Chalo said:
This is the calculator I use most: https://leonard.io/edd

Thanks. But what is OSB in this context? (Obviously not oriented strand board

)

speedmd · Dec 3, 2017

Buk___ said:
speedmd said:

Sapin is only to outside of flange and spoke head interface of the rim.

Click to expand...

Hm. Maybe I misinterpret you, but I don't think that can be right. Their "rim thickness" setting is a direct addition to the calculated length.

Also, as they are calculating the longer of the two measurements ...

Spoke head interface - side = tire side of rim. At least that is what is pictured. They are adding something and no where do they tell you what or for why. The leonard is a good one also.

Chalo · Dec 3, 2017

Buk___ said:
Chalo said:

This is the calculator I use most: https://leonard.io/edd

Click to expand...

Thanks. But what is OSB in this context? (Obviously not oriented strand board )

Offset Spoke Bed. The distance from the rim centerline where spokes attach.

Buk___ · Dec 3, 2017

Chalo said:
Offset Spoke Bed. The distance from the rim centerline where spokes attach.

Ah. Okay. Visually, it looks like the holes might be alternately offset very slightly, but if they are its a tiny amount. So little I'm not actually sure that they are.

I've also found it impossible to measure. There is simply no convenient surface or edge on this rim to provide an accurate reference datum

That said, I tried feeding in a 1mm offset to a couple of the calculators and it made less than 0.1mm difference to the length; and as I'm rounding to the nearest, higher mm, I guess I can ignore it.

Chalo · Dec 3, 2017

With most rims, you can disregard any offset value, even if the holes are visibly staggered. That parameter is for rims that are drilled off center to reduce dish, or for rims that have two sets of holes drilled side by side.

Which spoke length calculator?

Buk___

10 kW

speedmd

10 MW

docw009

1 MW

Buk___

10 kW

Chalo

100 TW

Buk___

10 kW

speedmd

10 MW

Chalo

100 TW

Buk___

10 kW

Chalo

100 TW

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