The link points to an episode of a podcast, but the headline topic about 32 in wheels is also available in text form.
And just to get it out of the way, in ISO/ETRTO parlance, such a wheel/rim would be described as 686 mm rim diameter, which is the second number necessary to match a wheel to a tire.
The article discussed the upcoming prospect of 686 mm mountain-bike wheels, noting the benefits of aesthetics for taller riders and roll-over capabilities on rough terrain, among others. But I’ve commented before about how the bicycle is a living record of technological advances and the benefits of the hub-spoke wheel, so I have to view the suggestion of a future with 686 mm wheels in that context.
Compared with 29ers (626 mm rim diameter), the obvious change is a larger diameter. This increases the hub’s ground clearance but also means the trailing edge of the front wheel swings a wider arc when turning. Forks necessarily have to be built taller to accommodate, and may require reinforcing to achieve the same flexural strength. Rake angles might have to be adjusted to avoid foot-wheel contact, or the wheelbase elongated.
For the wheel itself, increasing the diameter linearly increases the material needed for the rim, at a rate of pi. But if the spoke count remains the same, more material is needed to keep the same strength, as there’s more distance between spoke holes. A wider diameter also changes the spoke angle, which either reduces sideways strength – less relevant for road bikes but somewhat relevant for mountain bikes that will slide the back wheel – or needs a wider hub, which adds weight and implicates the frame design.
As with all engineering, these changes can be made, but to what end? What paramount objective would make all these changes worthwhile in the MTB space?
At this time, the article says that only the tire was showcased, and that Trek is investigating how it might be employed in new bikes. And I’m not going to unduly poo-poo the idea at this stage, but it’s not immediately clear that the benefits will be monumental. But if there are smaller benefits, I’m all ears. After all, Cannondale does their single-fork design and while they’re the only one doing it, that doesn’t disqualify its tangible benefits. Maybe 686 wheels will find a niche.
That said, I’m also not totally married to the idea that 29ers/626mm is the ideal size either, although I do think it’s sufficient for common use-cases. And all my bikes are uniform in using 626 mm wheels. That it is also a common tube size for road and MTB is just icing on the implementation cake.
