Simulation
Classified Drivetrain at the World Championship
Drivetrain configuration analysis for competitive cycling time trials, including the mountain time trial of the Tour de France and the UCI World Championship time trial in Rwanda, examining the performance influence of hub gear ratio selection under race-realistic conditions.
Links & Resources
Context
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 maintain optimal cadence across varying terrain — a factor with direct metabolic consequences. Power output required at a given speed changes nonlinearly with gradient, and a rider who runs out of useful gear ratios on a key section pays a disproportionate time penalty.
With the Classified PowerShift hub, a second effective chainring ratio becomes available inside the rear hub, engaging or disengaging in under 200 ms under full pedalling load. This changes the trade-off space for drivetrain configuration considerably: the front is clean and fixed, while the rear hub provides the coarse ratio step previously handled by the front derailleur.
Analysis
This work examines the influence of drivetrain configuration on cycling performance across two specific time trial scenarios: the mountain time trial stage of the Tour de France and the UCI Road World Championship time trial in Rwanda. Both courses present distinct gradient and cadence challenges.
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 tested. The simulator then integrates power, speed and energy expenditure over each course to quantify the time difference associated with different drivetrain choices.
The central practical question — when to deploy the hub ratio change, and what chainring and cassette combination to pair it with — depends on course gradient profile, rider power curve, and the efficiency characteristics of each ratio combination. These interactions are not always intuitive, and simulation provides a more reliable guide than rule-of-thumb estimates.
Presentation
This work was presented at the 10th Science & Cycling conference in Lille, held ahead of the Tour de France. The presentation included theoretical derivations, simulation methodology, experimental validation data from the test rig, and race-specific case studies.