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Spoke length fudge factor

Old 10-19-20, 11:21 AM
  #1  
deacon mark
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Spoke length fudge factor

I have a Kinlin rim with 285 ERD. I measured it myself. The spokes all go top nipple and frankly I am a bit surprised they were not too long but the wheel tensions up fine not issue. I want to replace that rim and use another Kinlin that has ERD of 588. Will that work to you think and I am reusing the spokes of course than the nipples as 14mm. I don't want to buy new spokes because at some point just buy another wheel is a better option. I would just like to have the spare wheel and the hub is fine.
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Old 10-19-20, 12:03 PM
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plug the numbers from the previous hub into a spoke calculator. how much longer of spokes do you technically need for new rim? 3mm of ERD is not a lot, so it's likely just fine. I would think that would mean your spokes are within 1.5mm of long enough. if you're pushing pat 2mm of too short, you might want different spokes. I'd do the calculation first.
don't use longer nipples to make spokes that come up short "long enough." that's a lousy kludge for amateurs who don't care about doing things right the first time so they last.

Last edited by mack_turtle; 10-20-20 at 08:32 AM.
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Old 10-19-20, 01:58 PM
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Originally Posted by mack_turtle View Post
Don't use longer nipples to make spokes that come up short "long enough." that's a lousy kludge for amateurs who don't care about doing things right the first time so they last.
Here is a better explanation than "you're stupid/lazy". It does a good job explaining that the spoke needs to be long enough to support the head on the nipple, and longer nipples don't have more thread engagement.


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Old 10-19-20, 02:38 PM
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deacon mark
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I already have the 14mm nipples that is with the current spokes I am using. I fully understand the issue of 12 vs 14 mm nipples. I just was asking about fudge factor on spoke length. I think it would work but now no sure if the rims are actually 588 ERD. The manufactures are not consistent with this and always best to measure yourself regardless.
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Old 10-19-20, 02:47 PM
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285 ERD? Did you mean 585?
Assuming so AND your new rim is 588, it'll basically make your spokes seem 1.5mm shorter.

"The spokes all go top nipple..."Do you mean the top of the nipple or to the screw driver slot?
IF the top of the nipple, your spokes should fit the "larger" rim better.
Crap in, crap out.
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Old 10-19-20, 09:48 PM
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Originally Posted by deacon mark View Post
I already have the 14mm nipples that is with the current spokes I am using. I fully understand the issue of 12 vs 14 mm nipples.
Are you sure?
It depends on the brand...
If you go to DT Swiss spoke calculator and run the same rim/hub measurements with 12mm, 14mm and 16mm nipples, you will see that the 14mm one needs a 1mm shorter spoke compared to 12mm, and 1 more mm shorter for 16mm. I snatched this figure somewhere quite a while ago:

DT Swiss nipples
-- for every 2mm of length they add 1mm of thread.

This is not the case for Sapim and others, those probably follow what mack_turtle and aggiegrads say. So if you have 14mm Sapim nipples going to 14/16mm DT Swiss may get you extra 1/2mm. I understand the problem with the nipple breakage at the head, but we should probably ask DT Swiss engineers about it

Also, there is a database of ERDs and some other data: Browse Rim Database | Freespoke - may be of some use for you.
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Old 10-20-20, 04:34 AM
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Originally Posted by csport View Post

DT Swiss nipples...
Ive seen that pic too, and it has made me wonder.
It seems very difficult to build a wheel with the precision needed to get full thread engagement in the head using their 16 mm nipples. Youd need to hit required tension and bottom out pretty much simultaneously.
and then what about later trueing? Youd be left with a one-way margin.
Now, the bike biz has certainly had its moments of less than brilliant engineering, so maybe this is DTs contribution to the hall of shame.
Or full head thread engagement isnt as important as conventional wisdom would have us believe.
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Old 10-20-20, 06:46 AM
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Originally Posted by dabac View Post
I’ve seen that pic too, and it has made me wonder.
It seems very difficult to build a wheel with the precision needed to get full thread engagement in the head using their 16 mm nipples. You’d need to hit required tension and bottom out pretty much simultaneously.
and then what about later trueing? You’d be left with a one-way margin.
Now, the bike biz has certainly had its moments of less than brilliant engineering, so maybe this is DT’s contribution to the hall of shame.
Or full head thread engagement isn’t as important as conventional wisdom would have us believe.
I think folks worry too much about bottoming out. I still strive for perfection in spoke length calculations, but based on my observations from tons of wheels coming through here for repairs, where sometimes spokes are protruding well beyond the nipple ,and supported by this view from Ric Hjertberg I now worry less about spokes being a little too long.
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Old 10-20-20, 07:02 AM
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Originally Posted by Dan Burkhart View Post
I still strive for perfection in spoke length calculations
Would that be to measure ERD and calculate spoke length to meet bottom of slot? I then round up to nearest 2mm since I always use double wall rims, and so ok if a little spoke protrudes. The video by Bill Mould on spoke position in nipple is also good.
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Old 10-20-20, 11:49 AM
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Originally Posted by deacon mark View Post
I have a Kinlin rim with 285 ERD. I measured it myself. The spokes all go top nipple and frankly I am a bit surprised they were not too long but the wheel tensions up fine not issue. I want to replace that rim and use another Kinlin that has ERD of 588. Will that work to you think and I am reusing the spokes of course than the nipples as 14mm. I don't want to buy new spokes because at some point just buy another wheel is a better option. I would just like to have the spare wheel and the hub is fine.
DT Swiss (and SAPIM, at least those bought in my country) nipples that have 14, and 16 mm length do have their threads starting lower within the nipple, so, when tightening spokes, threads on the nipple will start burring on the spoke's unthreaded part if you try to screw the nipple so much that the spoke ends up flush with the back side of the nipple (perfectly aligned with the slit).

So, yes, you could use 14, or 16 mm long DT Swiss, or SAPIM nipples, and for all the measurement purposes, it will be analog to using 1, or 2 mm longer spokes, respectively.

However, that will also result in the top part of the nipple (outer most) not being supported with the spoke inside of it. And can cause even good quality brass nipples to break off. Experienced something just like that (4th chapter talks about the failure):
Custom built wheel with spokes too short
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