Low Spoke Numbers, pt 1

July 04, 2022 3 Comments

Reduced spoke counts became a mass trend that continues today. Part fad, part function—it affects us all. Let’s explore the topic of spoke count and try to answer the question: what is the correct spoke number?

The 36 Spoke Era
For a century spoke number remained stable at 36, a choice that, despite its relatively high density, has advantages:

1. Compasses and drafting tools are marked in degrees, 360 per revolution—dividing by 10 is ultimately simple. 36 is a familiar number, easily shared and adopted.
2. Bicycles use wheel diameters of 20”–29”, convenient for the human body and the terrain we navigate. 36 spokes allows enough room between nipples for wrench turning.
3. Steel wire so successfully holds high tension that a high number makes only a small weight—72 spokes and nipples = only one pound.
4. High spoke density provides lots of support, permitting a wide range of rim materials—wood, steel, aluminum, and composites.

So bicycles propelled by 36 spoke wheels swept the planet.

1. First came the era of wood rims, widely used and dominant for competition (1900–1950).
2. Post WWII, aluminum developed for aviation allowed hollow shapes, rim hooks for demountable tires, and wing-like profiles with lower wind resistance (1950–2000).
3. The arrival of composites (carbon fiber, etc.) permitted complex, large aerodynamic shapes without serious weight penalty (2000+).

The Beginning of Low Spoke Numbers
Aerodynamic awareness arrived to cycling suddenly in the early 1980’s. In 1983 Rory O’Reilly (US National Team) ran aerodynamic tests at the University of Washington tunnel, discovering a nearly direct correlation between wind resistance and spoke number—half the spoke number = half the aerodynamic drag—a big surprise. We then built an 20 spoke front wheel on which he won the first US Pan American cycling gold (kilo, Bogota, 1983). 20 was a radical number for an event like the kilo.

Many low (16–24) spoke wheels were used by the US to win 9 medals at the 1984 LA Games. Regardless of their precise role in winning, low spoke counts were off to a conspicuous start and began appearing worldwide.

Building those wheels showed that rims had advanced further than we appreciated. 36 spokes was now often overkill. Experimentation revealed that spokes could be missing and wheels still retain satisfactory strength. A major chapter in wheel design began with the crossing of two unrelated trends—rim technology and aerodynamic goals.

Tinkerers cannot resist breaking rules and bushwhacking off the beaten path. We rode wheels that were too small, too light, too cheap, etc. just for curiosity and excitement. Some wheel tinkerers in the 1980’s were hard to miss:

1. Mavic created the Gitane TT bike in 1980 for Hinault. Note the aero downtube, faired head tube, hidden control wires, 24H wheels, hidden seat binder bolt, reversed front brake… all radical for the time.
   
2. Roval introduced clever low spoke count wheels in 1979.
   Note the radical features: hidden nipples, bladed spokes, flange fairings, straight pull spokes, and large section rim.

Managing Loads 

1. The hub provides the bracing angle (width between flanges), the rim and spokes further define the structure—a stronger rim needs fewer spokes and vice versa.
2. The sum of spoke tensions affects a wheel’s capacity for load—more spokes at lower tension is equivalent to fewer spokes at higher tension.
3. A more rigid rim distributes loads over more spokes so, for a given force, it can resist deformation with less spoke support.
4. If a spoke breaks, a more rigid rim can maintain trueness with less spoke support.

Wheel design is a balancing act—a low spoke number can be offset by a stronger rim and higher tension. A high spoke count like 36, takes much of the burden off the rim and spokes—a forgiving environment tolerant of lesser materials and build quality. One of the bicycle’s great accomplishments is its success in impoverished situations.

IMO
The availability of advanced materials and aerodynamic ideas aren’t enough to explain the continued popularity of low spoke numbers. Aerodynamics is of low value to most riders. Benefits accrue at speeds they rarely maintain. Much of the popularity of low spoke count wheels must be owed to fashion, to aspirations—like riding in a professional team uniform. No harm unless you think you’re going faster!

The industry pushes trends as do fashion scenes—trying to accelerate cycles of adoption and obsolescence. The good news is that millions of low spoke wheels (especially the common 20 x 24 road combo) are in use with very, very few complaints.

Is there a right number? There are too many variables—combinations, balancing factors, aesthetic concerns, riders, and budgets to begin to define what is a "right" spoke number. If you get down to a specific application, experience is the only guide. Common sense argues for themes like:

1. Minimize complexity, weight, and expense when there is little benefit.
2. Err on the conservative side—safety first! Weather, gravity, and road conditions can’t be controlled—that’s enough uncertainty without adding risky wheels.
3. Practicality always counts—use equipment that’s available, even if not perfect—this is the way of cyclists.
4. Dismiss bias about spoke numbers and approach situations with an open mind. Absorb the free lessons that come your way. 
5. Experiment and test but on yourself and on your own time. You are a builder to serve the needs of riders, not the other way around!
   

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