On Spoke Length (A Rant)
Proper spoke length is critical to building consistently reliable wheels. That’s not hyperbole, and it’s also not hard to do. It accounts for why I’ve had so very many WTF moments when repairing broken spokes in production wheels over the years. The frequency with which I see high-end carbon wheels in my shop with a spoke that has sheared at the nipple is excessive and totally unnecessary… preventable with proper spoke length calculation in almost every case.
- Threads fill threads. Bueno!
- A little long, no problem
- A little short, disastrous
I’m seriously confounded that so many premium wheel brands continue to spec their builds with spokes that are too short. It creates a fatal flaw in the system, allowing stress to localize at the last thread from the end of the spoke. As a wheel cycles many thousands of times, the accumulated stress work hardens the wire and the spoke breaks; when the spoke is too short this often causes the spoke to shear at that last thread. This failure is easily avoided by adding a millimeter or two to the length of the spokes so that the void where the thread is cut is filled by the threads of the nipple, preventing stress from being focused at this spot. So simple, and at Verum Velo that’s precisely what we do.
The above spokes are too short.
Here, threads meet threads.
Configuring wheels with slightly longer spokes has the added benefit of improving nipple reliability. We most often build with anodized alloy nipples. With spokes that are a little short and don’t run through the head of the nipple, alloy nipples can fail by having the empty part of the nipple head shear (tink, tink, tink). We are confident building with alloy nipples in part because of our approach to spoke calculation, because by filling the threads in the head of the nipple with spoke threads they will not shear (no tink, tink).
It gets worse before it gets better. If you have a wheel that suffers from short spoke syndrome (shall we call it SSS?) there’s no little blue pill to cure it. The only solution is to chop out all the spokes and replace them with longer ones. Otherwise, once one breaks the others are soon to follow.
I’ve repaired so many wheels with SSS, and am constantly scratching my head as to how anyone who understands how a bicycle wheel works could overlook such as simple solution to one of the most common causes of spoke/wheel failure. It’s maddening! Thus, Verum Velo is my happy place.
Here endeth the rant.
Charles