The big leap forward in bicycle wheel design arrived in the mid-nineteenth century with the introduction of highly tensioned wire spokes. This technology, borrowed from the aviation industry, enabled wheels to be both weight-bearing and light. Since then, whilst wheel design has certainly been advanced, it is fair to say that to the casual cyclist at least, a degree of mystique has crept in and surrounds the practice of wheel building.
Mike Burrows is a leading cycle builder with a reputation for producing ground-breaking bikes. Burrows takes a thoroughly pragmatic approach to designing, so when choosing the right materials for a job he rejects received wisdom in favour of hard facts. Everything is put under the microscope, spoke patterns included.
Spokes on a wheel are arranged either crossed or radial. Crossed spokes leave the hub at a tangent and pass one or more opposing spokes before reaching the rim. Radial spokes go directly from the hub to the rim, without crossing any other spokes. Each style has its merits and uses, but the relative stiffness and ride quality of the various patterns is the subject of some misinformation, which Mike puts to bed in this film.
To scientifically test how the different spoke patterns affect the ‘stiffness’ of a wheel – i.e. how much force is required to deform it – Mike built a test-rig. By putting load onto a wheel and gauging how much it flexed, the rig measured the effect tire deflection (where the bike contacts the road) has on rim deflection (something the rider may feel).
On the first wheel Mike tested, tire deflection of 16mm caused just 0.4mm of flex at the rim. In other words, on this wheel a bump in the road would impact the rim only ever so slightly, and would have a negligible effect on the comfort of the ride. In fact, such a tiny deflection would only be picked up by a sensitive measuring tool, not a rider’s backside.
The test was repeated on different wheels, and Mike found that rim deflection under load was essentially the same with any spoke pattern, radial or crossed. So, it would be a mistake to say one particular spoke pattern is stiffer than another.
Mike Burrows points out that what can be felt by the rider is a wheel’s lateral (sideways) stiffness. When sprinting, a wheel is put under side-load from the force put on the cranks. As wheels are thin structures, they will inevitably yield to these loads. Asymmetrical rear wheels with a cassette are particularly susceptible to this.
Mike Burrows also observes that people sometimes have a tendency to assume something is wrong if they are not used to it. For example, a solid disc wheel (one without spokes) might produce a noise going over a pothole. This does not mean the wheel is any less stiff or weaker than a spoked wheel, it is simply that the spoked wheel would not have made the noise.
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