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  1. #1
    Senior Member Jtgyk's Avatar
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    Miscalculated spoke length

    I entered Specs I thought were right (bad info on my FH M510 hub) into DT s spoke calculator
    and ordered my spokes a couple days ago (DT Apline III)

    After searching for the specs again I realized the discrepancy and re-entered the correct flange to center measurements. This dropped the right hand spokes from 290 to 289mm.
    Do I need to re-order for the right side or will the 290mm spokes be OK?

    Full disclosure of info:
    Hub Deore fh-M510
    Rim Alex DH19 ERD=599.7
    Alpine III spokes w/ 12mm brass nipples.
    36 spokes 3 cross

    Sorry to be a pain, but it's my first rebuild and I'd like to get it right.
    Last edited by Jtgyk; 05-13-10 at 02:58 PM.
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    Type 1 Racer rydaddy's Avatar
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    I'd say you are fine.

  3. #3
    Bill
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    Some builders actually recommend using plus or minus 1mm from the calculated length. I think some spoke length calculators do that for you, not really sure about that.
    I agree with rydaddy that you'll be OK with what you ordered but not having actually checked your calculations I'd say it does depend on the rim and hub measurements being accurate. I prefer to do my own rim and hub measurements and verify with several available databases. Go For It!
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  4. #4
    Senior Member Jtgyk's Avatar
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    Yeah I should have done my own measurements to begin with....but live and learn.
    At least I didn't go crazy and order a box of 100.

    From what I've gleaned from the interweb, I'm guessing a drive side tension between 110 and 120 kgf...leaning toward the upper limit because of the 9spd freehub and greater dish in the wheel?
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  5. #5
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    If you are talking about the rear drive side spokes you will probably need the shorter spokes. These are the highest tensioned spokes on the bike and have more potential to stretch through time. Can you exchange them?

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    There's a couple of millimiters room on either side of the "perfect" length so 1mm isn't going to make a difference unless your measurement was already off and it becomes 1mm too far. IMO most spoke calculators tend to give results on the short side anyway, so I'm fairly sure you'll come out OK, possibly even better off than if you hadn't made the mistake.
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    You'll be fine, especially if your rim is double-walled so that even if the spokes stike through the nipple by a whole mm they still nowhere near your tube.

  8. #8
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    The risk of a too long spoke has nothing to do with how it fits the nipple. The risk is of running out of threads before reaching the needed tension.

  9. #9
    Senior Member Jtgyk's Avatar
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    Quote Originally Posted by Al1943 View Post
    The risk of a too long spoke has nothing to do with how it fits the nipple. The risk is of running out of threads before reaching the needed tension.
    This is mainly what I was worrying about. Is there a way to extend the threaded section? I've seen where you can have spokes cut to length. I assume they add the threads after they are cut.
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  10. #10
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    Quote Originally Posted by Jtgyk View Post
    This is mainly what I was worrying about. Is there a way to extend the threaded section? I've seen where you can have spokes cut to length. I assume they add the threads after they are cut.
    Typical spoke and nipple combinations from the same manufacturer have sufficient thread for the spoke to go about 2mm or more above the top of the nipple. Since your spoke calculator probably gave you a length that comes up 1mm shy of the top of the nipple, that gives you a margin of error of 3mm, and you're using 1mm of it. You'll be fine.
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  11. #11
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    Quote Originally Posted by Jtgyk View Post
    This is mainly what I was worrying about. Is there a way to extend the threaded section? I've seen where you can have spokes cut to length. I assume they add the threads after they are cut.
    Yes but it's generally not advisable. Good threads are "rolled" not cut. Cut threads are more likely to break.

  12. #12
    Senior Member Jtgyk's Avatar
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    Quote Originally Posted by FBinNY View Post
    Typical spoke and nipple combinations from the same manufacturer have sufficient thread for the spoke to go about 2mm or more above the top of the nipple. Since your spoke calculator probably gave you a length that comes up 1mm shy of the top of the nipple, that gives you a margin of error of 3mm, and you're using 1mm of it. You'll be fine.
    Cool! That's nice to know. Now I'll just have to wait for the spokes to show up and take my time sith the build.
    I wounder how much the shop will charge to fix my repair?

    I'll get back and let you know how well ( or badly) this turns out...
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  13. #13
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    Quote Originally Posted by Al1943 View Post
    Yes but it's generally not advisable. Good threads are "rolled" not cut. Cut threads are more likely to break.
    The spoke threading devices used also roll the threads.

    It isn't a matter of strengh, it's a matter of the relative diameters of the threaded and unthreaded sections. You can't cut the thread into a spoke because the blank OD is smaller than the thread OD.

    For cut threads the blank is equal to the thread's major (or outside) diameter, and for rolled threads the blank is equal to the "pitch" diameter, or halfway between the major and minor diameter. In the rolling process no material is removed, but material is flowed from the "valleys" to form the "peaks".
    Last edited by FBinNY; 05-13-10 at 08:51 PM.
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  14. #14
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    Quote Originally Posted by FBinNY View Post
    The spoke threading devices used also roll the threads.

    It isn't a matter of strengh, it's a matter of the relative diameters of the threaded and unthreaded sections. You can't cut the thread into a spoke because the blank OD is smaller than the thread OD.
    rolled threads are typically more fatigue resistant, less prone to stress cracking, and more resistant to stripping. Doesn't change your main point, but that's (one of the reasons) why they're rolled.

  15. #15
    Senior Member mrrabbit's Avatar
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    My data says this is a symetrical hub...

    Spoke length I get is 290.59mm using your rim ERD.

    Chances are pretty good you'll be just fine...

    =8-)
    4000+ wheels built since 1984...

    Disclaimer:

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  16. #16
    Type 1 Racer rydaddy's Avatar
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    I've had spokes cut that were too long before (I too made the mistake of trusting the hub dimensions online). They were DT Comps and the guy used a Phil cutter. Although I agree rolled threads have an advantage, I don't think cut threads are all that bad.

  17. #17
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    Quote Originally Posted by rydaddy View Post
    I've had spokes cut that were too long before.... They were DT Comps and the guy used a Phil cutter. Although I agree rolled threads have an advantage, I don't think cut threads are all that bad.
    For the record, your spokes that were cut with a Phil spoke machine had rolled threads. It isn't a question of rolled vs cut threads being better or worse, it's the simple fact that you cannot cut threads in 14mm spokes because the diameter of the wire is too small and you'd only get half of the thread profile. To cut the thread for a 14g nipple you'd need to start with a 13g spoke.

    For those interested here's a link to a site which explains the difference between rolling and cutting threads.
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  18. #18
    Senior Member Jtgyk's Avatar
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    Quote Originally Posted by FBinNY View Post
    For the record, your spokes that were cut with a Phil spoke machine had rolled threads. It isn't a question of rolled vs cut threads being better or worse, it's the simple fact that you cannot cut threads in 14mm spokes because the diameter of the wire is too small and you'd only get half of the thread profile. To cut the thread for a 14g nipple you'd need to start with a 13g spoke.

    For those interested here's a link to a site which explains the difference between rolling and cutting threads.
    Thanks for the explanation and site.
    So the fact that the body of the spoke is smaller in diameter than the threads will allow me to take up the extra 1mm since there is no physical "stop"
    (of course at the expense of having fewer threads engaged)?
    I'll have to see whether, in practice, this will weaken that particular connection too much and be on the look out for failure at the nipple.
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  19. #19
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    Quote Originally Posted by Jtgyk View Post
    Thanks for the explanation and site.
    So the fact that the body of the spoke is smaller in diameter than the threads will allow me to take up the extra 1mm since there is no physical "stop"
    (of course at the expense of having fewer threads engaged)?
    I'll have to see whether, in practice, this will weaken that particular connection too much and be on the look out for failure at the nipple.
    Close, but still no cigar.

    The spoke is smaller than the thread, but only by 1/2 the thread height, so the nipple will still jam when it's first thread hits the last thread on the spoke. The extra length available is because spoke companies tolerance their spokes and nipples around the concept of the ideal height being to the top of the nipple, so they leave room for over or under that ideal.

    Thread strength is unaffected because the structural part of the nipple is the head (which is why it's important that spokes come well up into it), and the extra thread engagement below the head is meaningless either way. Think of a bolt, you put a nut on the end & and once the thread goes beyond the nut, the arrangement doesn't get stronger or weaker because of bolt above the nut, or unused threads below.

    When you get the spokes, thread one nipple down all the way, and that'll show you how far up the spoke can come before you run out of thread.
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  20. #20
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    Quote Originally Posted by Al1943 View Post
    If you are talking about the rear drive side spokes you will probably need the shorter spokes. These are the highest tensioned spokes on the bike and have more potential to stretch through time. Can you exchange them?
    Spokes don't strech.

  21. #21
    Senior Member Jtgyk's Avatar
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    Quote Originally Posted by FBinNY View Post
    Close, but still no cigar.

    The spoke is smaller than the thread, but only by 1/2 the thread height, so the nipple will still jam when it's first thread hits the last thread on the spoke.
    Well poop! I knew there had to be a catch.

    Quote Originally Posted by FBinNY View Post
    The extra length available is because spoke companies tolerance their spokes and nipples around the concept of the ideal height being to the top of the nipple, so they leave room for over or under that ideal.

    Thread strength is unaffected because the structural part of the nipple is the head (which is why it's important that spokes come well up into it), and the extra thread engagement below the head is meaningless either way. Think of a bolt, you put a nut on the end & and once the thread goes beyond the nut, the arrangement doesn't get stronger or weaker because of bolt above the nut, or unused threads below.

    When you get the spokes, thread one nipple down all the way, and that'll show you how far up the spoke can come before you run out of thread.
    It's a good thing they do...so far in the Alpine III the size I've been able to find online is 288mm then it jumps to 290mm (what I had ordered) the calculator at DT (for the drive side) came up with a real length of 288.8 and rounded it up to 289. I'll, hopefully be able to get enough tension with the 290's.
    I'll just have to see when they get here.
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  22. #22
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    Quote Originally Posted by davidad View Post
    Spokes don't strech.
    Yes they certainly do. I've had DT Revolutions stretch as much as 3 mm. These were measured before installation and after replacement.
    I have not seen 2 mm straight gauge spokes stretch, but I don't use straight gauge spokes.
    Last edited by Al1943; 05-14-10 at 02:46 PM.

  23. #23
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    Quote Originally Posted by Jtgyk View Post

    It's a good thing they do...so far in the Alpine III the size I've been able to find online is 288mm then it jumps to 290mm (what I had ordered) the calculator at DT (for the drive side) came up with a real length of 288.8 and rounded it up to 289. I'll, hopefully be able to get enough tension with the 290's.
    You may be just fine with the 290's but I would have ordered the 288's. Even if they build right there is a possibility that they may stretch over time. I'm having to replace the driveside rear spokes on two of my wheels sets because the Revolution spokes stretched so much over a period of 5 years that the nipples bottomed out on the spoke threads and it was no longer possible to increase tension. Same thing happened to me on a set of MAVIC factory built Helium wheels.
    The Alpine spokes should not stretch as much as Revolutions.

  24. #24
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    Quote Originally Posted by Al1943 View Post
    Yes they certainly do. I've had DT Revolutions stretch as much as 3 mm. These were measured before installation and after replacement.
    I have not seen 2 mm straight gauge spokes stretch, but I don't use straight gauge spokes.
    Spokes don't stretch unless they're stressed beyond their elastic limits. Otherwise they lengthen and shorten like springs within their elastic range as the loads change. If your spokes stretched over time your wheels are too tight for the spoke you're using, and/or the stresses of use are taking the spokes beyond their design working capacity.

    Assuming the same material, the ideal spoke tension is proportional to the cross-sectional area of the spoke, so a DT revolution might only be able to be tensioned about half as tight as a 14g plain gauge spoke. This is one of the reasons that I usually build high dish wheels using thinner spokes on the left flange.
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  25. #25
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    Quote Originally Posted by FBinNY View Post
    Spokes don't stretch
    They certainly do stretch under high tension.
    I quit using Revolutions on the drive side rear because of the stretch.
    If you use the DT Swiss calculator it automatically rounds down spoke lengths in almost every calculation. For Revolutions it now rounds down an extra 1 mm for drive side rear spokes. It did not round down the extra 1 mm at the time I built those wheels.

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