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  1. #1
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    Is something up with the DT calc?

    Ive used the DT swiss calc many times. Maybe hundreds of times. Its always been my favorite calculator, and its always worked great for me.

    Except the last two times. I measured everything the same way I always have, using the same tools I always have, and I've come up with too-long spokes twice in a row now.

    ... did something change? Its entirely possible that I screwed up twice in a row, but im ending up with spokes 2-3mm too long. I can throw washers under the nipples and they work, but that still seems odd.

    Just me? Anyone else having some calculator issues lately?

  2. #2
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    My spokes have been too long on the last two builds using the DT calculator. It's too late tonight to investigate. Could be a coincidence.

  3. #3
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    You too? Hmm. Maybe they did some silly length compensation. It was perfect for so long!

    I have a feeling that if I order 2mm shorter spokes for this new wheel, they'll end up crazy short and I'll bone myself on the whole build.

  4. #4
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    Did you try another calculator to cross reference the result???

  5. #5
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    I compared results from Pro Wheel Builder calc. and find a massive discrepancy. D.T. Swiss calcs coming up shorter, sometimes as much as 7mm. Further, checking some D.T. lengths from some time ago for the same build against some calcs. made today there seems to be an increase in lengths of 1 to 2 mm's in the new calcs.
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  6. #6
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    Seems the same as usual. I entered the measurements for the wheels I currently own and it came back with the spoke lengths that I'm actually using. My spoke lengths are either dead on or at most 1mm on the long side due to rounding since I only have even spoke lengths available to me. For what it's worth I have an over 15 year age gap in my wheels, so if something's changed it should show up.

  7. #7
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    Try a different calculator and compare the results https://www.wheelpro.co.uk/support/s...h-calculators/

    I also found that the DT calculator gave me too long spoke lengths.

  8. #8
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    I've been burned by DT's calc twice now and no longer use it for spokes. Though it is still handy for adding up total weight.

  9. #9
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    What are the measurements? And what rims/hubs?

    I can punch them into QBP for you and see what it says.

    Also, do not forget to factor in nipples and spokes. Most of the calc's do not factor in spoke stretch, something like DT Revo's stretch a ton (upwards of 2mm) while building.

    DT 14 and 16mm nipples also require shorter spokes than 12mm ones.

    ERD should always be measured, in a few spots, it's by far the most crucial measurement.
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  10. #10
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    uh, no. DT revolutions are a 1.5mm spoke that will stretch less than 1mm at 130kgf.

  11. #11
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    Quote Originally Posted by Schulze View Post
    uh, no. DT revolutions are a 1.5mm spoke that will stretch less than 1mm at 130kgf.
    Maybe its not 2mm of stretch, but I always round down 14g spokes by .5mm-1mm. And an additional 1mm shorter for the revos. I build to 120-135kgf for most wheels.

    The first mm could be from the calculator wanting the spokes to be longer than what I personally wanted to see sticking past the head of the nipple. I did a lot of reading before building with revos and nearly everyone said to go a bit shorter than standard 14g spokes. 1mm shorter worked and I have always stuck with it.

    Again, just my experience with wheels that I have built with revos.
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  12. #12
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    Quote Originally Posted by MikeDee View Post
    Try a different calculator and compare the results https://www.wheelpro.co.uk/support/s...h-calculators/

    I also found that the DT calculator gave me too long spoke lengths.
    I'm only getting marginal differences.
    IIRC, Roger Musson's calculator has been updated to account for spoke stretch so that could be the difference right there.

    Is something up with the DT calc?-m6yny3k.jpg

  13. #13
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    In that link I posted, it shows that there are correction factors in the DT calculator for different types of spokes and nipples. Choosing the wrong ones in the DT calculator could account for the spoke length discrepancies.

  14. #14
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    Are you measuring erd yourself?
    Are your center to flange measurements measured to the center of the flange, not one side?
    Are your flange diameter measurements measured center to center of the spoke holes?

    Assuming the measurements were taken the same way that I would measure them, this is the result that I got from Q, and the length spokes that I would use:

    261.45, I would cut at 261
    260.06, I would cut at 259.5

    Is the spoke sticking out of the top of the nipple by 2-3mm? My numbers are shorter than yours, but not by 3mm. Best guess is the ERD is not correct.

    This is the method I use for measuring ERD. https://www.parktool.com/blog/calvin...e-rim-diameter

    Using that method, and rounding down the spoke length, will still result in the spoke coming up above the bottom of the slot in the nipple, but below the top of the nipple. In my book, perfect.

    From Q on exactly how to measure the hub:

    To measure hubs accurately, all you need is a reliable measuring caliper.

    Flange Diameter:

    Measure the distance across the flange from spoke hole center to spoke hole center. Be sure to check both flanges as they are not always the same diameter.

    Center To Flange:

    Measure locknut to locknut and divide by 2.
    Measure distance from each locknut to the center of the nearest flange.
    Subtract the locknut to flange measurements from the results of step 1 for both the left and right side, respectively.
    Attached Thumbnails Attached Thumbnails Is something up with the DT calc?-capture.jpg  

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  15. #15
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    For the DT calculator, I always pick 12mm nipples, and comp spokes, I know DT nipples position differently. I'm using all the same methods and even the same tools I've always used, for years now.

    For ERD, l I take 4-6 measurements, toss out the highest and lowest, and average the rest. Probably overkill, but if it is, how am I getting spokes so far off?

    I need to do this in CAD and get exact, uncorrected values.

  16. #16
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    Quote Originally Posted by One Pivot View Post
    For the DT calculator, I always pick 12mm nipples, and comp spokes, I know DT nipples position differently. I'm using all the same methods and even the same tools I've always used, for years now.

    For ERD, l I take 4-6 measurements, toss out the highest and lowest, and average the rest. Probably overkill, but if it is, how am I getting spokes so far off?

    I need to do this in CAD and get exact, uncorrected values.
    With this many calcs giving you so many similar results, it has to be bad data getting put in.

    Something changed. What rim is it?
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  17. #17
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    Quote Originally Posted by MikeDee View Post
    Try a different calculator and compare the results https://www.wheelpro.co.uk/support/s...h-calculators/

    I also found that the DT calculator gave me too long spoke lengths.
    Using aerolites and squorx nipples gives a net correction of 0 so that can't be the source of why my spokes were long. I estimate they were 2mm too long.

    Using the same inputs, the Wheelpro and DT calcs are within 0.7mm. So I don't know.




  18. #18
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    Quote Originally Posted by MikeDee View Post
    In that link I posted, it shows that there are correction factors in the DT calculator for different types of spokes and nipples. Choosing the wrong ones in the DT calculator could account for the spoke length discrepancies.
    DT uses a fixed correction factor which doesn't account for spoke tension (both sides of a dished wheel get the same correction) whereas the Wheelpro calculator does account for the tension difference from dish when calculating how much the spoke stretches.

  19. #19
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    Nipple washers are good for taking up 1/2mm of length. Squorxs nipples will take up the extra 2mm of spoke thread if your spokes are threading 2mm above the top of your standard nipples. Sapim double square nipples are good for an extra 1mm to 1.5mm of spoke length, depending how long the threads on the spoke are.

    I would also compare the numbers to the rim manufacturers ERD. Some lightweight rims compress a lot and others have a chamfer in the spoke hole that allows the nipple to sit deeper in.

  20. #20
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    Yeah, I used aluminum Sapim DSN so the build went smoothly aside from more turns required. From what I can tell, they will tolerate +4mm for two reasons: The extra threads and the way aluminum threads fold over if you go too deep. There is still full thread engagement so nothing lost.

  21. #21
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    Since the DT calculator has correction factors for their spokes and nipples, unless you are using these exact components, you will get inaccurate results.

    I can't figure out though why they are adjusting for different nipples because don't you measure ERD with the nipples you are intending to use?

  22. #22
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    Did you read my previous posts MikeDee? Their correction factors are insignificant.

  23. #23
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    Is something up with the DT calc?

    Quote Originally Posted by Schulze View Post
    Did you read my previous posts MikeDee? Their correction factors are insignificant.
    I don't follow. There are correction factors for spoke nipples in the link I posted. What do you consider insignificant? Some of the nipples have a -2mm correction factor.

    I use Wheelsmith spokes and nipples. Trying to match these up to an equivalent DT spoke and nipple to use the DT calculator might be a source of error if I choose unwisely.

    I like my spoke length to be at the bottom of the slot in the spoke nipple and no more than flush with the top. That's like 1mm in tolerance? Not much and any source of error like these correction factors should be minimized.

  24. #24
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    -2mm only on the 16mm nipples. I used squorx nipple in the calc and Sapim dsn in the build, basically identical nipples.

  25. #25
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    interesting discussion. I'm taking a wheel building class this spring, and I'm using the option in the class to build wheels that I'll take home and ride (usually students just use supplied parts, and leave them behind to be reused, I suppose). Which means I have to buy all the parts beforehand, and bring the correct-length spokes. I ran some test calculations through a few spoke length calculators (including DT's), and assuming the numbers I input were all the same, they all spat out spoke lengths that were the same.

    I actually have the rims and spoke nipples I'll be using on hand now (as of today), and I just need 1 more tool to calculate the ERD according to the method posted by Park Tool (which the instructor recommends). Now, to be fair, I'll be using a lot of DT parts (rims, nips, spokes) and I'll certainly be paying attention to any discrepancies between spoke length calculators.

  26. #26
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    Quote Originally Posted by Harold View Post
    interesting discussion. I'm taking a wheel building class this spring, and I'm using the option in the class to build wheels that I'll take home and ride (usually students just use supplied parts, and leave them behind to be reused, I suppose). Which means I have to buy all the parts beforehand, and bring the correct-length spokes. I ran some test calculations through a few spoke length calculators (including DT's), and assuming the numbers I input were all the same, they all spat out spoke lengths that were the same.

    I actually have the rims and spoke nipples I'll be using on hand now (as of today), and I just need 1 more tool to calculate the ERD according to the method posted by Park Tool (which the instructor recommends). Now, to be fair, I'll be using a lot of DT parts (rims, nips, spokes) and I'll certainly be paying attention to any discrepancies between spoke length calculators.
    You might want to pick up a book like The Bicycle Wheel by Jobst Brandt or Professional Guide to Wheel Building by Roger Musson. Lots of useful information in those as well as at Sheldonbrown.com and Mike T's wheelbuilding site at http://miketechinfo.com/new-tech-wheels-tires.htm

  27. #27
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    Try Spokomat

  28. #28
    since 4/10/2009
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    Quote Originally Posted by MikeDee View Post
    You might want to pick up a book like The Bicycle Wheel by Jobst Brandt or Professional Guide to Wheel Building by Roger Musson. Lots of useful information in those as well as at Sheldonbrown.com and Mike T's wheelbuilding site at Wheels
    I bought Musson's book.

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