Upgrading your wheels is a rite of passage for many cyclists, and choosing which set to plump for – an outlay that can range from several hundred to several thousand dollars – can involve poring over spec sheets and trying to decipher marketing jargon.

We have tested a great many wheels in the wind tunnel already, to provide comparative data across a whole range of models, but we also wanted to interrogate how certain design factors, namely wheel depth, spoke count, and spoke material, affect speed.

subsequent clarification on the rules only outlines increased velocity as a risk factor, with no mention of wheel stability, despite the fact that Swiss Side’s ardent rebuttal to the ruling leans almost entirely on wheel stability.

As a general rule of thumb, deeper wheels (in our experience on the road) are generally harder to handle in crosswinds, and more prone to buffeting, which certainly is a safety factor that could justify a wheel depth rule, but it’s also true that not every deep wheel is harder to handle than every shallower wheel, and given that the UCI has only leant on the increased velocity in its documentation of the ruling it seems valid to test those claims in isolation and, if necessary, call them out.

Cyclingnews has contacted the UCI for clarification on the justification of the wheel depth rules in the context of the results outlined in the latter section of this article, given that (without wishing to spoil the party) we found very little difference in terms of speed when you only change wheel depth.

Jump to: Wheel depth

X-Lab AD9, which we happened to have on hand from aero testing earlier that day, and tested without a rider so as to provide the cleanest dataset possible. The differences were, we assumed, likely to be quite small, and so adding a rider would have provided a more realistic dataset, but the additional margin of error could well have overshadowed the differences and made the data effectively meaningless.

As usual, we tested across a sweep of yaw angles (the angle at which the wind hits the rider), from -15º to +15º in 5º increments. This, we feel, represents the majority of riding and racing scenarios for the performance cyclist. We tested at a single speed, 40km/h, which we feel represents a fast amateur race pace, or perhaps a breakaway day for higher-level competitors. It’s also fast enough to hopefully show sufficient differences, as aerodynamic differences scale with increasing magnitude, the faster one rides.

In order to account for any manufacturing differences across batches of the same tyre, not only was the same model of tyre used (a 28c Continental GP 5000 S TR), at the same pressure, but the exact same physical tyre was swapped across wheelsets just to be on the safe side.

We swapped both wheels to study the effect of a whole wheelset swap.

Our error margins are the same as our bike only tests, which we conducted on the same day, namely a CdA difference of 0.0007, or 0.58 watts at 40km/h.

which were then affected by the ban, forcing the brand to develop a 65mm version. This would have caused a huge tooling cost to create the physical moulds, let alone the R&D and lost revenue from illegal wheels, all for 0.135km/h. Even with a wider swing, from the 55mm deep Hadron 3 to the illegal 68 version, the difference is a paltry 0.585km/h. Hitting the ground at 49.5km/h is going to suck just as much as it will at 49km/h.

Swiss Side itself claims the 68mm Hadron is has a 0.5w drag advantage over the 65mm deep version. I’m not sure what speed this was at, but assuming the industry standard-ish 40km/h, we can use this as a sense check on our extrapolations. Half a watt is half the difference we found at 40km/h between the mid-depth Hunts and the deeper Hunts, which itself resulted in a velocity difference at 450 watts of 0.36km/h. Inputting some hypothetical CdA figures to artificially create a 0.5w difference at 40km/h results in a 0.18km/h velocity differential, so our extrapolations are in the right ballpark.

While the law is well-intentioned, it is symptomatic of the UCI’s approach to safety: Regulate equipment, with less of a focus on course design and other systemic changes that could actually make meaningful improvements. Regulating wheel depth will slow riders down, but according to our data at least, it is to such a small degree as to be basically meaningless.