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June 02, 2019 2 Comments
Wire spokes for bicycles come in three main types—straight gauge, single-butted, and double-butted.
Of these three, single-butted have been sleepers, hanging around in the fringes, not much used or discussed. However, their role is growing and they will inevitably become the workhorses of the wheel world. Why?
Double butted are expensive
There are few practical ways to make a spoke thinner in the center and they’re all expensive. One is swaging, a slow and intense process of hammering wire as it rotates. Another is pressing, which is also slow and requires huge force. Drawing is awkward to do on a section between two larger diameters. The die must open and close which entails time and money. Small diameter steel wire is hard to make thinner.
Single-butted spokes can be make more economically especially if the butt is made at the same stage as the head and elbow. Wire diameter can be increased (called upsetting) in the target area more easily than reduced along the center.
Huge stocks of wrong-length double butted spokes
Think of all the 298-308mm spokes used in 700C shallow rim wheels of the past. Today we see more short spokes for deep rims, 27.5 and 26” wheels, and e-bikes. Many longer 2.0-1.8-2.0mm spokes can be to 2.0-1.8mm single-butted. There’s huge freedom for length, the spoke is lighter than double-butted, and 15G (1.8mm) nipples are 14% thicker walled.
Spoke Cutting and Threading
Thousands of builders cut and thread spokes in their own workshops using overstock spokes as well as blanks. Their threads are often superior to factories and they can make shorter thread length (6mm rather than 10mm) so threads are fully embedded in the nipple. It’s been showed this can largely eliminate breakage at the nipple.
Custom builders also choose rims, nipples, and lacing patterns that reduce kinks in the spoke. Kinks at the nipple encourage breakage in the threads and are the reason double-butted spokes are double.
Spoke makers offer many options
Not all double-butted spokes are candidates for shortening. Here are a few that are: DT Competition, Sapim Force and Race, Pillar PDB 14/15, and CN DB454. All have 1.8mm centers. Additionally, DT Alpine, Sapim Strong, and Pillar PSB are already single-butted, and easy to shorten.
Many builders work for a wage and as a public service but others also consider aesthetics. My personal preference with wire wheels is lighter spokes. They seem visually more interesting and I like their tiny contribution to elasticity and moment of inertia. Single-butted spokes qualify but they also bring an appealing economy. It's hard to argue with frugality that costs little or no function.
In the quest for smart, versatile, economical solutions for future wheel building, single-butted spokes are coming your way—and it’s good news!
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