Spoke length mystery

Q

qwerkus

10 kW
Joined
Jul 22, 2017
Messages
794
Hello,

I'm quite new to wheelbuilding, and could use some advice regarding spoke length. Out of 3 wheels I just build using the same software to calculate spoke length (spocalc from sheldon's website), 2 set fit perfectly and one set turns out to be over 2mm too long. I triple check all measures, and always get the same results: 287/286mm

The rim is a DT-Swiss 545D 700C with an ERD of 605mm
The hub is a shimano dynamo: DH-3D72 (dia 70mm, flange left 20mm, flange right 29mm, hole 2.6mm)
36 spokes, 3x cross

The only hypothesis I could come up with to explain the length mismatch (besides me making a big mistake somewhere) is that the hub is used. Yet I don't see how this would off the calculation by over 2mm. So any advice here would be greatly appreciated.

Thank you for your time.
 
qwerkus said:
Hello,

I'm quite new to wheelbuilding, and could use some advice regarding spoke length. Out of 3 wheels I just build using the same software to calculate spoke length (spocalc from sheldon's website), 2 set fit perfectly and one set turns out to be over 2mm too long. I triple check all measures, and always get the same results: 287/286mm

The rim is a DT-Swiss 545D 700C with an ERD of 605mm
The hub is a shimano dynamo: DH-3D72 (dia 70mm, flange left 20mm, flange right 29mm, hole 2.6mm)
36 spokes, 3x cross

The only hypothesis I could come up with to explain the length mismatch (besides me making a big mistake somewhere) is that the hub is used. Yet I don't see how this would off the calculation by over 2mm. So any advice here would be greatly appreciated.

Thank you for your time.
Click to expand...

Does the rim have offset holes?
 
Buk___ said:
Does the rim have offset holes?
Click to expand...

Seems so: I'd say around 1-2mm though I could not find any info about this on the manufacturers page. Do you think that could explain the length mismatch ? Though the 2 other rims also have offset holes, and it didn't change a thing.
 
qwerkus said:
Buk___ said:
Does the rim have offset holes?
Click to expand...

Seems so: I'd say around 1-2mm though I could not find any info about this on the manufacturers page. Do you think that could explain the length mismatch ? Though the 2 other rims also have offset holes, and it didn't change a thing.
Click to expand...

I found discrepancies between two online spoke length calculators and received advice on other calculators. Maybe that thread will help you :)
 
I know you said you triple checked all measures, but does that include measuring the spokes actually sent to you? Perhaps that set simply got cut too long, and the others were done right?
 
2 mm seems like it wouldn't be a big problem. Just grind some off the ends if needed.
 
fechter said:
2 mm seems like it wouldn't be a big problem. Just grind some off the ends if needed.
Click to expand...

exactly, build up the wheels nice and tight and as long as you can get them up to proper spoke tension just grind off any excess protruding past the spoke nipples with a dremel tool.. if the spokes are too long to reach proper tension then measure the spoke length and order a couple millimeters shorter and try again.. use a few different spoke calculating programs and average out any variation..
 
Thank you all for your help. I measured the spokes again using the sheldon brown technique (spoke + ruler hanging over another spoke) and although I was surprised to find up to 0.5mm difference between 2 spokes, the average fits the description.

Yes, the problem is that the spokes are too long to be tensioned: the nipple hits the threading collar before I can begin serious tensioning. So shorter spokes are indeed required, yet I would really like to understand how this could happen, in order to avoid it next time.

I tried a couple more calculators (sapim and dt swiss): they give the same results.
 
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