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Question on spoke length calculation

Old 08-29-22, 02:09 PM
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Harhir
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Question on spoke length calculation

I want to put a hub dynamo in one of my wheels. The hub dynamo is a Shimano DH-3D37 which has a 3.6mm offset. The rim is a Velocity Dyad 406 (20"). According to a tire spoke calculator the difference in spoke length between left and right side is about 1.1mm.
167.3mm on the left and 168.4mm on the right side. I think with this small of a delta I can order the same length spoke for both sides. I was thinking about 168.0mm for each side. That should give me enough room on either side. Any concerns here doing that?
Below is also a photo from the calculator out put which can be found here:
https://www.kstoerz.com/freespoke/
Thanks

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Old 08-29-22, 08:03 PM
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I'd 168 on both.
You have a double wall rim, so you don't have concerns about a spoke being so long it protrudes into the rim strip.
.4mm short is only .016".
If using thinner spokes, they may stretch a "couple/few" extra .1mm.
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Old 08-29-22, 10:22 PM
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I second Bill's suggestion to split the difference and use the same spoke for both sides, but with one caveat.

I don't know if you measured the ERD, or pulled it from a spec sheet, but that is the most critical dimension. Most of the calculators will bring the end of the spoke out to the ERD entered. If the thickness of the nipple head isn't allowed for, that means that the spoke will end at the BOTTOM of the nipple head, not 0-1mm shy of the top.

My advice is to measure the ERD yourself, either allowing for the nipple heads, or if measuring from the nipple seat add 2-3mm (according to rounding) to the calculated length.
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Old 08-30-22, 08:50 AM
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Originally Posted by FBinNY View Post
I second Bill's suggestion to split the difference and use the same spoke for both sides, but with one caveat.

I don't know if you measured the ERD, or pulled it from a spec sheet, but that is the most critical dimension. Most of the calculators will bring the end of the spoke out to the ERD entered. If the thickness of the nipple head isn't allowed for, that means that the spoke will end at the BOTTOM of the nipple head, not 0-1mm shy of the top.

My advice is to measure the ERD yourself, either allowing for the nipple heads, or if measuring from the nipple seat add 2-3mm (according to rounding) to the calculated length.
Yes I pulled the ERD from the spec sheet in the tool and from the manufacturers web site. I can't measure it right now since the wheel is currently used in my bike. I wanted to order the new spokes and hub dynamo before I take it apart. But I am not concerned since this is a double walled rim. So even if the spokes protrude beyond the nipple head I should be fine. According to the drawing on the manufacturers web site there is about 8mm room between the two walls.
https://www.velocityusa.com/product/rims/dyad-406
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Old 08-30-22, 09:03 AM
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Originally Posted by FBinNY View Post
I second Bill's suggestion to split the difference and use the same spoke for both sides, but with one caveat.

I don't know if you measured the ERD, or pulled it from a spec sheet, but that is the most critical dimension. Most of the calculators will bring the end of the spoke out to the ERD entered. If the thickness of the nipple head isn't allowed for, that means that the spoke will end at the BOTTOM of the nipple head, not 0-1mm shy of the top.

My advice is to measure the ERD yourself, either allowing for the nipple heads, or if measuring from the nipple seat add 2-3mm (according to rounding) to the calculated length.
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Old 08-30-22, 09:50 AM
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Originally Posted by FBinNY View Post
I second Bill's suggestion to split the difference and use the same spoke for both sides, but with one caveat.

I don't know if you measured the ERD, or pulled it from a spec sheet, but that is the most critical dimension. Most of the calculators will bring the end of the spoke out to the ERD entered. If the thickness of the nipple head isn't allowed for, that means that the spoke will end at the BOTTOM of the nipple head, not 0-1mm shy of the top.

My advice is to measure the ERD yourself, either allowing for the nipple heads, or if measuring from the nipple seat add 2-3mm (according to rounding) to the calculated length.
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Old 08-30-22, 10:18 AM
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Not to introduce any more confusion or controversy, but I usually use spoke nipple washers with a no-eyelet rim like a Dyad. Washers add about 1mm to the required spoke length. Based on the Freespoke numbers, and using washers, I would probably go with 168 on the left and 170 on the right. And the washers are probably overkill anyway. But that’s just me.

And — based on 40-odd years of wheel building — I strongly agree that there’s no substitute for measuring the ERD yourself. Roger Musson (wheelpro.co.uk) has a good template for doing this using a printed scale and a couple of junk spokes cut to length.
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Old 08-30-22, 10:47 AM
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I'm new to this, but what does this have to do? I mean why simply not procure them as they are.
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Old 08-30-22, 10:55 AM
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While some Al rims of an aero shape have their special spoke "washers" most all other rims have a flat enough spoke bed to allow the nipple to seat well. Most of these rims are made with a thick enough spoke bed to not need the stress relieving aspect of a nipple washer. I consider the Dyad to be one of these rims not needing a washer for structural reasons (can't say I have ever seen a cracked Dyad rim). BUT using a washer as a low friction device (a thrust washer of sorts) is not a bad choice. Al rims with no eyelet will have more friction/grip on the nipples. So when tensioning up the spokes some of the effort to turn nipples is from this friction. This added friction can mislead the truer/builder in thinking that the spokes are reaching a good tension level, when the spokes are still lower in tension then ideal.

I also agree with the others who welcome back Francis. He has greater patients and tolerance for those who post than I do. Although I think we share the same goals in trying to help them. Andy
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Old 08-30-22, 10:57 AM
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Originally Posted by Johnathonbenfie View Post
I'm new to this, but what does this have to do? I mean why simply not procure them as they are.
Can you rephrase your question? Whay does "this" and "them" reefer to? Andy
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Old 08-30-22, 11:08 AM
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Originally Posted by Andrew R Stewart View Post
While some Al rims of an aero shape have their special spoke "washers" most all other rims have a flat enough spoke bed to allow the nipple to seat well. Most of these rims are made with a thick enough spoke bed to not need the stress relieving aspect of a nipple washer. I consider the Dyad to be one of these rims not needing a washer for structural reasons (can't say I have ever seen a cracked Dyad rim). BUT using a washer as a low friction device (a thrust washer of sorts) is not a bad choice. Al rims with no eyelet will have more friction/grip on the nipples. So when tensioning up the spokes some of the effort to turn nipples is from this friction. This added friction can mislead the truer/builder in thinking that the spokes are reaching a good tension level, when the spokes are still lower in tension then ideal.

I also agree with the others who welcome back Francis. He has greater patients and tolerance for those who post than I do. Although I think we share the same goals in trying to help them. Andy
Good point, and I should have been more clear … I generally use the washer in an attempt to reduce friction. I agree that the Dyad has plenty of thickness in the spoke bed and I’ve never seen a cracked Dyad either.
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Old 08-30-22, 02:46 PM
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Thanks everyone with the idea to use washers to reduce friction. I have never used them so far but it makes total sense to me. So far I have built less than 10 wheels and my experience is limited. My biggest concern is always to get the best tension. I do have the park tool tension meter but this tool does not really work on small wheels with double cross pattern.
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