Wheel Design How-To Part 1

I think it’d be interesting to write a little bit about what all went into a wheel design for Boyd cycling this past year. The rims which are currently in production I’m super proud of because as a Pro-level racer they’re a set of wheels that I’d choose over almost any other wheels, most of this design work took place in 2014. This will probably be broken up into several manageable parts, enjoy.

Design Goals

Arguably the most important part of any design is setting out the initial design requirements. This sets the ‘ship of design’ on course and becomes very difficult to change once you have sunk costs in a given design philosophy. Working with Boyd (who has extensive feedback of what cyclist want out of their wheels) we set out a number of goals to strive for: 

  • Aerodynamics
  • Wide Rim/Tire Compatibility
  • Clincher rim brake track heat dissipation
  • Tubeless compatibility

We weighted these components in a design matrix to help evaluate different rim shapes.

The primary improvement we hoped to achieve was to design an Aerodynamic wheelset. A secondary but closely related goal was to design a wheelset to accommodate a wider tire. Traditionally road cyclists use narrow road tires measuring 21mm or 23mm, however the current trend is towards wider tires 25mm and larger. The larger tire has numerous advantages over a narrow tire: better grip, improved rolling resistance and is less prone to puncture. The two main disadvantages are weight and aerodynamics. The goal of an Aerodynamic wheelset and a wide tire are closely coupled, especially for the increasingly prevalent clincher wheelset. This means that some of the negative aerodynamic effects of a wide tire can be negated with proper design of the rim.

Composite clinchers have, in the past, had a dubious reputation. The thermal conductivity of Carbon Fiber is two orders of magnitude less than Aluminum. Low thermal conductivity coupled with the low melting point of the resin used in the some Carbon Fibers meant that under heavy braking the large heat built up through friction was not dissipated as it is with Aluminum (where heat build-up is not a concern). A two fold effect then takes place: the heat in the rim is transferred to the air in the tire, increasing the tire’s pressure and load on the rim hooks, and the material around the brake track softens allowing the rim to open up. Since braking is always heavier in the front, this leads to a catastrophic blow-out. This is a relatively rare failure, but due to its catastrophic nature (front wheel, downhill, usually at high speed), has been a fairly singular deterrent for people purchasing a carbon clincher wheelset.

The final goal is achieving improved tubeless compatibility with the rims. A tubeless rim replaces a traditional tire/tube setup with a heavier duty tire with stronger bead and latex based sealant. Nearly every Mountain Bike rim sold today is setup without tubes due to their puncture resistance, lower tire pressure that can be used, and better grip. There has been much slower adoption among road users. This can be attributed to a number of factors including but not limited to: limited tire availability, limited tubeless ready rim availability, the unproven technology factor, and difficulty of setup. There are essentially no disadvantages to producing a rim that is compatible with a tubeless and normal tube setup versus a tube setup alone.



One Comment

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