Classified Drivetrain at the World Championship

Engineering Question

Competitive time trialing places unusually precise demands on drivetrain configuration. The choice of chainring size, cassette range, gear-ratio steps and hub system affects not only mechanical efficiency but also the ability to hold an optimal cadence across varying terrain — a factor with direct metabolic consequences. Because the power required at a given speed changes nonlinearly with gradient, a rider who runs out of useful gear ratios on a decisive section pays a disproportionate time penalty.

Model and Assumptions

The analysis combines steady-state drivetrain efficiency modelling with a physics-based cycling performance simulator. Mechanical efficiency is computed as a function of load, speed and gear combination for each configuration, and the simulator then integrates power, speed and energy expenditure over the course to estimate the time associated with each drivetrain choice. The Classified PowerShift hub adds a degree of freedom to this space: a second effective chainring ratio inside the rear hub, engaging or disengaging in under 200 ms under full pedalling load, so the front remains clean and fixed while the hub supplies the coarse ratio step once handled by the front derailleur.

What the Analysis Compares

The framework is applied to two contrasting time-trial scenarios — the mountain time trial of the Tour de France and the UCI Road World Championship time trial in Rwanda — each with its own gradient and cadence profile. The aim is not a single headline number but a comparison: which chainring and cassette to pair with the hub, and when to deploy the hub ratio change, given a particular course profile and rider power curve. This work was presented at the Science & Cycling conference held ahead of the Tour de France.

Significance

These interactions are not always intuitive — a small efficiency difference can be outweighed by a better-placed gear step, or the reverse — and the right configuration depends on the specific course and rider. Simulation provides a more reliable guide to these choices than rule-of-thumb estimates, which is what increasingly turns drivetrain selection in competitive time trialing into a modelling problem.