Timeline for Cause of broken spokes (pictures included)
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
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| Sep 1, 2020 at 12:11 | comment | added | ojs | @Peter-ReinstateMonica if you look up FEM analysis of a bike wheels or measure it yourself, you'll see that the rim is deformed so that the tension is reduced in bottom four spokes and slightly increased in all others, including diagonally downward pointing ones. | |
| Sep 1, 2020 at 12:04 | comment | added | Chris H | w.r.t. the last para, the cause is important. More than 3-4 unexplained failures may well need a rebuild on new spokes, but I lost 3 outer drive side spokes and replaced all 9 because of a known cause - them getting in a fight with the chain. The rebuild lasted until the hub wore out with no further issues. | |
| Sep 1, 2020 at 12:02 | comment | added | Chris H | Those who say the wheel stands on the bottom spoke aren't wrong, given that they clarify that this is a reduction in tension, rather than compression, but it's not a helpful picture. All spokes are in tension all the time if there's nothing wrong with the wheel. | |
| Sep 1, 2020 at 10:04 | comment | added | juhist | You misunderstand how a wire spoked wheel works. A wire spoked wheel does not hang from the topmost spoke. It stands on the bottommost spoke, and for this reason the spoke tension needs to be high -- the bottommost spoke can only support standing equal to its preload. The topmost spoke does not experience a significant increase in tension. For more of how wire spoked wheel works, read "The Bicycle Wheel" by Jobst Brandt. | |
| Sep 1, 2020 at 9:25 | comment | added | Peter - Reinstate Monica | Shouldn't the momentarily horizontal spokes also experience load, since the wheel tries to become egg-shaped, with a wider horizontal diameter, under load? This is prevented by the horizontal spokes taking up tension. I suppose that insufficient tension on all spokes imposes the load on too few spokes, overstressing them; in a properly built wheel the upward facing ones carry the load while the horizontal ones keep the wheel in shape, and no spoke ever is without tension, so the rim is "worked" (cyclically deformed) less and the cyclic load difference in each spoke is smaller. | |
| Sep 1, 2020 at 3:48 | comment | added | Chris Stratton | This is almost right, and more useful than the post from Nathan Knutson which misses the issue of insufficient tension causing fatigue. But a the hub does not "hang" from the upper spokes, it "stands" on the lower ones. As one can indeed not push a rope, this fact illustrates why it is critical that the dynamic force never exceed the preload tension of those lower spokes! They can only function as "compression" members when the compression force is less than the preloading tension. | |
| Aug 31, 2020 at 20:09 | history | answered | Criggie♦ | CC BY-SA 4.0 |