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  1. #1
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    Broken Spoke - mid-spoke

    Maybe this isn't that strange, but it seems so to me. Last fall I built a set of wheels using H+Son Alchemy rims, Sapim Race spokes, and BHS hubs, 24/28 Radial/2x and I weigh 155 lbs. Fast forward over a thousand miles and no issues until today, not even pinging or cracking (I followed MikeT's site and Roger Musson's book closely and de-stressed the heck out of both wheels).

    Today a front spoke broke in the middle of the spoke. I wasn't too sure what to make of it, but set out to replace it. While shaking the rim trying to fish out the nipple - yes I let the nipple loose without thinking - the spoke next to the broken spoke broke, again in the middle, shooting the nipple and half the spoke out like a rifle. Thankfully it wasn't aimed at my face.

    I replaced both, and trued the wheel with no problem. Tension is relatively constant all around, using the pluck method, and based on pitch less than the drive side rear, but greater than the NDS.

    I don't recall seeing any damage to the spokes. However, a while back part of the speed sensor on the front fork came loose and bounced off the spokes as it was falling off the bike. But it's plastic and I wouldn't expect it could cause significant damage.

    Any thoughts on the cause of the breakage? Could it be due to too much tension?

  2. #2
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    As you're probably aware, spokes rarely break in the middle. It's almost always at the bend - and even then it's rare. It must be 20 years since one of mine broke. IMO spokes breaking in the center do it from damage or faulty metal.

    As spokes are only tensioned to a fraction of their overall strength (1/3rd? 1/2?) the chances of them breaking from too much tension is probably nil. The rim would fail (crack) long before this would happen.

    And front wheel spoke breakage is very unusual.

    You've had two break. If the wheel was mine I'd re-build with new spokes.
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    Mike T's home wheelbuilding site - dedicated to providing Newby wheelbuilders with motivation, information and resources.

  3. #3
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    I'm with MikeT. Perhaps the batch of spokes was defective.

  4. #4
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    I would also offer twist as one more possible cause of spoke breakage to the ones already mentioned. Twist from windup that was not brought back may create a weak spot that eventually could cause breakage.
    The OP mentioned that he stress relieved the wheel several times however it should be mentioned that stress relieving the spokes does not relief any twisting that may have happen during tensioning or from stuck nipples that don't let the spokes untwist during use.
    The suggestion Mike made to rebuild the wheel is a good one.
    With bicycles in particular, you need to separate between what's merely true and what's important.

  5. #5
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    Thanks for the input. I taped the spokes during the build so I think I can rule out excessive twist. Based on everything I've read, damage or defective metal is probably the culprit. Just didn't know if I was missing something.

    Looks like I'll be checking out some new spokes soon! Heck, while I'm at it maybe I'll bite the bullet and build some new wheels with the v2 Pacenti rims!

  6. #6
    grizzly moderator
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    Quote Originally Posted by MikeinJax View Post
    Thanks for the input. I taped the spokes during the build so I think I can rule out excessive twist. Based on everything I've read, damage or defective metal is probably the culprit. Just didn't know if I was missing something.

    Looks like I'll be checking out some new spokes soon! Heck, while I'm at it maybe I'll bite the bullet and build some new wheels with the v2 Pacenti rims!
    Taping the spokes gives a good indicator against spoke twist. Another way to check that is to tension the spokes until they become relative tight and then draw a line down the spoke with a Sharpie. If the line twists then the spoke twists. I think it may be a bit easier than the tapes. Black Sharpie works nice with silver spokes and silver Sharpie with black spokes.

  7. #7
    Talks too much, that is..
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    Do you have the spokes? I'd be very, very interested in seeing close up pictures of the break. You can tell a lot about the material and the cause by looking at the exposed material right at the break. Unfortunately, unless you happen to have macro photography as a second method of disposing of your income this might not be possible.

    If nothing else, I'd check them very closely for anything resembling a nick. If they aren't nicked, I'd contact Sapim. They may ask for them.

  8. #8
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    In my experience (which is limited compared to some of the gurus here) breaks in the middle have always been traced back to corrosion. The owner stored the bike in the vicinity of caustic chemicals. Usually chlorine for the pool or fertilizer of some sort. Only once has it been been natural corrosion, but the bike was stored outdoors in a coastal region. A couple of times the owner didn't even know they had anything in the garage/shed until the spokes broke and I sent them looking for something.

  9. #9
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    Spoke Pic

    Here are the best I can do of the second spoke to break - sorry no expensive macro equip. I don't know if you can see it, but the break is uneven and one area is shiny while the other is dark which leads me to believe it was damaged, either through contact or defect. I'll try to contact Sapim to get their take.
    Attached Thumbnails Attached Thumbnails Broken Spoke - mid-spoke-img_0262.jpg   Broken Spoke - mid-spoke-img_0259.jpg   Broken Spoke - mid-spoke-img_0258.jpg   Broken Spoke - mid-spoke-img_0253.jpg  

  10. #10
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    Contacting Sapim is a good idea as their people might be able to analyze the break and tell you how it happened. They're easy to reach as I e-mailed them a few months ago with a question and they responded quickly. If you don't get much joy, contact me as I know the Sapim USA guy. He won't be able to give you a reason for the break but he might rattle some cages. Maybe we could all learn here as front wheel mid-span spoke breakage is quite rare,
    .
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  11. #11
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    Quote Originally Posted by Mike T. View Post
    Contacting Sapim is a good idea as their people might be able to analyze the break and tell you how it happened. They're easy to reach as I e-mailed them a few months ago with a question and they responded quickly. If you don't get much joy, contact me as I know the Sapim USA guy. He won't be able to give you a reason for the break but he might rattle some cages. Maybe we could all learn here as front wheel mid-span spoke breakage is quite rare,
    Thanks Mike and everyone who posted, I've sent an email through Sapim's website and will let you know what I find out.

  12. #12
    Talks too much, that is..
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    Not that I could tell much from the pictures, but I'm going with a nick in both of the spokes that broke. Crack propagation from a nick is something that can happen and results from the stress concentration that results. Even small nicks in large steel structural elements need to be addressed (usually by grinding or sanding out the nick) in order to avoid concerns.

  13. #13
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    Quote Originally Posted by Peter P. View Post
    I'm with MikeT. Perhaps the batch of spokes was defective.
    Absent the twist possibility or that somehow these spokes got nicked (stress riser/thinner cross section) then defective metallurgy seems most likely.

  14. #14
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    Does anyone know the best way to send the spokes to Sapim in Belgium? I have the address and Sapim are waiting for the spokes, but Fedex will not allow - says the commodity code is not allowed. I can try via USPS but I expect the same results and also I believe Belgium customs will open and inspect.

    Also, probably not smart but I took the same bike/wheels out again this weekend with the same results - another mid-spoke break on the front wheel, but on the left side whereas the previous breaks were both on the right. So, this wheelset is retired until I can respoke!

  15. #15
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    Quote Originally Posted by MikeinJax View Post
    Does anyone know the best way to send the spokes to Sapim in Belgium? I have the address and Sapim are waiting for the spokes, but Fedex will not allow - says the commodity code is not allowed. I can try via USPS but I expect the same results and also I believe Belgium customs will open and inspect.

    Also, probably not smart but I took the same bike/wheels out again this weekend with the same results - another mid-spoke break on the front wheel, but on the left side whereas the previous breaks were both on the right. So, this wheelset is retired until I can respoke!
    This is baffling. Why not send them via regular post? "commodity code"? If the customs declaration needs something, just list as "bicycle parts". But why not just snip the spokes 3" on each side of the break, tape 'em to a card and send as regular letter mail. Heck if they want all the spoke, chop it into 3" pieces. Creativity counts.
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  16. #16
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    Quote Originally Posted by Mike T. View Post
    . But why not just snip the spokes 3" on each side of the break, tape 'em to a card and send as regular letter mail. Heck if they want all the spoke, chop it into 3" pieces. Creativity counts.
    Yup. That's all they would need.
    With bicycles in particular, you need to separate between what's merely true and what's important.

  17. #17
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    Heard from Sapim today, say there is a metallurgical problem with the spokes and are sending out replacements!

    Looks like I'll be re-building soon.

  18. #18
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    Quote Originally Posted by MikeinJax View Post
    Heard from Sapim today, say there is a metallurgical problem with the spokes and are sending out replacements!
    Looks like I'll be re-building soon.
    Great news. I hope they treat you for your inconvenience.
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