Stability over speed? UCI provides new information to defend controversial wheel depth rule

“These changes are part of an overall approach aimed at ensuring ever safer and fairer competition conditions, in a context marked by rapid technological advances and a significant increase in racing speeds that could have an impact on rider safety,” read a statement that also covered other rule changes, including handlebar width.

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No further reasoning was given for limiting rim depth to a maximum of 65mm, though Swiss Side’s rebuttal to the ruling focussed heavily on wheel stability. With this discrepancy in mind it raised the question as to whether speed was the only factor considered, as our testing shows that increasing wheel depth does very little to affect velocity, to which the UCI responded:

“Wheel behaviour is governed by complex physical and aerodynamic phenomena that influence stability, steering and speed. Speed is indeed a contributing factor in the severity of injuries in the event of a crash; it therefore forms part — but not the entirety — of the criteria considered when introducing new regulations.

“The UCI does not address safety through a single isolated rule, but through a broader and coherent framework, of which equipment regulation is one component.”

It seems, therefore, that while speed was all that was communicated with the public, it was certainly not the only consideration. The governing body then goes onto to clarify:

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“There is a substantial body of scientific evidence demonstrating that increasing rim depth systematically leads to higher lateral forces, greater steering moments and increased sensitivity to gusts under crosswind conditions, particularly at higher yaw angles.

“Numerical and experimental studies show that deeper rims result in higher lateral force coefficients and increased steering moments under yawed flow. The front wheel is especially critical in this regard, as it directly governs steering, is the first exposed surface and concentrates the induced destabilising moment.

“While deeper rims may provide aerodynamic drag benefits at low yaw angles, these advantages diminish as yaw increases, whereas destabilising moments continue to rise. Under crosswind conditions, deeper rims increase the rotating surface exposed to asymmetric flow, further contributing to steering moments and instability.”

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By our reading of this it appears that speed was only a minor factor in the safety debate regarding equipment regulations, with wheel stability taking precedence. This begs the question: why was this not communicated at the time? Furthermore, it casts doubt on the other equipment regulations included in the 2026 suite, including bar width and gear restrictions.

Cyclingnews approached the UCI for further clarification as to the initial justification of the ruling, and was provided the following response:

“Please be advised that, as for all UCI regulations, the UCI analyses a wide range of characteristics and the potential impacts of any changes, as well as possible collateral effects. In this case, speed was one of several factors considered, alongside others such as stability, drive, control, dynamics, injury risk, comfort, mechanical cost etc.

“The detailed rationale underpinning each regulatory decision is however not published in full in UCI press releases, but further information and clarification may be provided upon request.”

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Will Jones

Senior Tech Writer

Will has been staying abreast of UCI equipment changes this season, and conducted lab testing to ascertain whether they would have any impact on overall race speeds. He’s also got countless hours of testing of wheels under his belt.

It must be said at this point that, as a general rule (from our own riding experience at least) that deeper wheels are harder to handle in gusty conditions. It’s not the case that every wheel with a depth greater than 65mm is less stable than every wheel with a depth shallower than 65mm, but the UCI must come up with rulings that are not only grounded in sound reasoning, but also enforceable. Basing a ruling around steering forces would be practically impossible to enforce, whereas a 65mm rim can be checked with nought but a ruler.

Safety regulations are key to a sport that is often inherently incredibly dangerous, as evidenced by the litany of injury stories on the pages of Cyclingnews, but proper communication of the reasoning behind said regulations is key for them to receive buy-in from all stakeholders and actually have the desired effect.