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Spoke length calculation question.

Old 09-08-22, 10:39 AM
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Buffalo113
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Spoke length calculation question.

Hello all,

Newbie to the forums, and definitely a novice when it comes to wheel building. This will be my third build, but I'm running into a technical problem I need assistance with.

I want to upgrade the hubs on a Giant SLR-2 42 wheelset and replace them with DT Swiss 350 hubs. The flange diameter for the DT Swiss is different from the existing hub, so I will need to replace the spokes as well, probably with Sapim Sprint or Strong. The problem I'm having is that they have different numbers of spokes on each side. The wheels have 24 spokes total, but one side has 16 and the other has 8. The side with 16 has a 3X cross pattern, and the side with 8 has a 1X cross pattern. From what I've seen, all of the online spoke length calculators assume a standard configuration of 12 spokes on each side for a 24H wheel. How to I calculate the spoke lengths for a wheel like this?

Thanks in advance.
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Old 09-08-22, 11:26 AM
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Dan Burkhart 
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Originally Posted by Buffalo113 View Post
Hello all,

Newbie to the forums, and definitely a novice when it comes to wheel building. This will be my third build, but I'm running into a technical problem I need assistance with.

I want to upgrade the hubs on a Giant SLR-2 42 wheelset and replace them with DT Swiss 350 hubs. The flange diameter for the DT Swiss is different from the existing hub, so I will need to replace the spokes as well, probably with Sapim Sprint or Strong. The problem I'm having is that they have different numbers of spokes on each side. The wheels have 24 spokes total, but one side has 16 and the other has 8. The side with 16 has a 3X cross pattern, and the side with 8 has a 1X cross pattern. From what I've seen, all of the online spoke length calculators assume a standard configuration of 12 spokes on each side for a 24H wheel. How to I calculate the spoke lengths for a wheel like this?

Thanks in advance.
Look for a feature on whatever calculator you are using to select between Normal ( J bend) straight pull, or triplet. You want triplet
Edit: So I just tried this on my mobile device which I have never used for this and that feature doesnít seem to be available on the calculator I use most frequently.
Havenít tried it on my computer lately but it used to be there
Alternatively you can do two calculations, one for 32 spokes and one for 16.

Last edited by Dan Burkhart; 09-08-22 at 11:40 AM.
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Old 09-08-22, 12:00 PM
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Originally Posted by Dan Burkhart View Post
Look for a feature on whatever calculator you are using to select between Normal ( J bend) straight pull, or triplet. You want triplet
Edit: So I just tried this on my mobile device which I have never used for this and that feature doesnít seem to be available on the calculator I use most frequently.
Havenít tried it on my computer lately but it used to be there
Alternatively you can do two calculations, one for 32 spokes and one for 16.
I thought I could do separate calculations for each side, which shouldn't be a problem for the side with 8 spokes, since those are spaced evenly along the rim, but if I make a 32H calculation for the other side, won't the hole spacing on the rim be wrong?

I will check the online calculators for the triplet feature.

Thank you.
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Old 09-08-22, 01:27 PM
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Are you sure the NDS is 1 cross? I'd expect radial.

Calculate for 32 and it'll assume 16 per side. Use that for your DS.
Calculate for 16 and it'll assume 8 per side. Use that for your NDS.
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Old 09-08-22, 11:47 PM
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Originally Posted by Bill Kapaun View Post
Are you sure the NDS is 1 cross? I'd expect radial.

Calculate for 32 and it'll assume 16 per side. Use that for your DS.
Calculate for 16 and it'll assume 8 per side. Use that for your NDS.
The OP is concerned that the calculations for 32 will assume the 16 on the DS are evenly spaced with 1/16 of the circumference between each spokes while they are actually paired with 1/24 between the close ones and 1/12 between the far ones. I imagine that would make a noticeable difference, but I don't know how to calculate that.

Looking at pics online, there does not appear to be a radial side on these.
https://www.giant-bicycles.com/us/sl...waAqcVEALw_wcB
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Old 09-09-22, 12:05 AM
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I did the math 15 years ago or so when I was still into triplet lacing

Get a copy of spocalc (or something else that will let you use fractions) and treat it as a 32 spoke wheel, but use 3.35 as the number of crosses on the drive side.
Treat the nds as a 16 spoke wheel as mentioned before.
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Old 09-09-22, 05:27 AM
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Originally Posted by Mackers View Post
I did the math 15 years ago or so when I was still into triplet lacing

Get a copy of spocalc (or something else that will let you use fractions) and treat it as a 32 spoke wheel, but use 3.35 as the number of crosses on the drive side.
Treat the nds as a 16 spoke wheel as mentioned before.
Or you could do another calculation for 36 spokes and split the difference between that and 32. I think that would get you within the fudge factor.
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Old 09-09-22, 06:39 AM
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Originally Posted by Bill Kapaun View Post
Are you sure the NDS is 1 cross? I'd expect radial.

Calculate for 32 and it'll assume 16 per side. Use that for your DS.
Calculate for 16 and it'll assume 8 per side. Use that for your NDS.
It is definitely not a radial, and there is definitely 1X on the NDS for the rear wheel. It is reversed for the front wheel. The 8 spoke side is on the DS.
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Old 09-09-22, 06:49 AM
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Originally Posted by Buffalo113 View Post
The wheels have 24 spokes total, but one side has 16 and the other has 8. The side with 16 has a 3X cross pattern, and the side with 8 has a 1X cross pattern. From what I've seen, all of the online spoke length calculators assume a standard configuration of 12 spokes on each side for a 24H wheel. How to I calculate the spoke lengths for a wheel like this?
A little trigonometry is needed:
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Old 09-09-22, 09:32 AM
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Originally Posted by JohnDThompson View Post
A little trigonometry is needed:
Yes, this is the equation given by Musson in his on-line book on wheel building. For radial you set x=0, and the cosine of zero is 1, and go ahead and calculate L. It can easily be different designs for the two halves of the wheel. The equation does not comment on the wisdom of all the different choices which might be made, but the book does. I used it to select spokes for my 40/32 spoke Rudge club-style wheels, with replacement aluminum rims.
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Old 09-09-22, 10:03 AM
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Originally Posted by Dan Burkhart View Post
Look for a feature on whatever calculator you are using to select between Normal ( J bend) straight pull, or triplet. You want triplet
Edit: So I just tried this on my mobile device which I have never used for this and that feature doesnít seem to be available on the calculator I use most frequently.
Havenít tried it on my computer lately but it used to be there
Alternatively you can do two calculations, one for 32 spokes and one for 16.
I found an online triplet lacing calculator called FreeSpoke. That is exactly what I was looking for. It even has the hub parameters already loaded in their databse. Thank you for pointing me in the right direction.
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