Which spoke length calculator?

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Buk___
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Which spoke length calculator?

Post by Buk___ » Dec 03, 2017 8:46 am

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

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speedmd
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Re: Which spoke length calculator?

Post by speedmd » Dec 03, 2017 11:08 am

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
Last edited by speedmd on Dec 03, 2017 8:00 pm, edited 1 time in total.

docw009
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Re: Which spoke length calculator?

Post by docw009 » Dec 03, 2017 11:54 am

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___
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Re: Which spoke length calculator?

Post by Buk___ » Dec 03, 2017 11:56 am

speedmd wrote:
Dec 03, 2017 11:08 am
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 ...

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Chalo
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Re: Which spoke length calculator?

Post by Chalo » Dec 03, 2017 12:30 pm

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.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Buk___
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Re: Which spoke length calculator?

Post by Buk___ » Dec 03, 2017 12:52 pm

Chalo wrote:
Dec 03, 2017 12:30 pm
This is the calculator I use most: https://leonard.io/edd
Thanks. But what is OSB in this context? (Obviously not oriented strand board :) )

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speedmd
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Re: Which spoke length calculator?

Post by speedmd » Dec 03, 2017 4:52 pm

Buk___ wrote:
Dec 03, 2017 11:56 am
speedmd wrote:
Dec 03, 2017 11:08 am
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 ...
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.

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Chalo
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Re: Which spoke length calculator?

Post by Chalo » Dec 03, 2017 5:42 pm

Buk___ wrote:
Dec 03, 2017 12:52 pm
Chalo wrote:
Dec 03, 2017 12:30 pm
This is the calculator I use most: https://leonard.io/edd
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.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Buk___
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Re: Which spoke length calculator?

Post by Buk___ » Dec 03, 2017 8:11 pm

Chalo wrote:
Dec 03, 2017 5:42 pm
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.

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Chalo
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Re: Which spoke length calculator?

Post by Chalo » Dec 03, 2017 8:45 pm

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.

Image

Image
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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