Simulation
Inside the Classified PowerShift Hub
Physics-based simulation and test-rig validation of the Classified PowerShift two-speed planetary hub, demonstrating how a compact rear hub can deliver the gear range of a front derailleur while sustaining efficiency above 99% across the full operating range.
The Concept
The Classified PowerShift hub removes the front derailleur from a road or gravel drivetrain by hiding a second gear ratio inside the rear hub. The mechanism is a two-speed planetary gear system with six planet gears. In direct drive at 1:1 ratio, the planetary stage locks as a single rotating unit, with no relative gear motion inside the hub. In the reduced ratio of 0.686, the sun gear is held fixed and the planet gears transfer torque between the cassette and the wheel — delivering a chainring jump roughly equivalent to moving from a 52-tooth to a 36-tooth ring.
The shift between ratios is near-instantaneous and can be performed under full pedalling load, which changes the practical calculus of gear selection on steep terrain considerably.
Engineering Validation
Planetary gears are not inherently inefficient. Designed carefully, with well-chosen gear geometry, bearing selection and lubrication, they can transmit power with minimal losses. The investigation applied a detailed physics-based simulation model to characterize the PowerShift hub's efficiency across its operating range, then validated those predictions against a purpose-built test rig.
The test rig provided controlled load and speed measurements across the range of conditions the hub sees in normal use. Model and measurement agreed closely. The hub achieves efficiencies above 99% across most of its operating range, with particularly strong performance at high-power, low-speed conditions — the regime that occurs when the reduced gear ratio is engaged on a steep climb.
The Wider Picture
An efficient hub is the enabling component, not the end of the story. A single-chainring setup with optimized chainline reduces chain articulation at the cassette, lowering friction in the chain-sprocket interface. Bottom bracket forces are reduced by the elimination of cross-chaining. Combined, the Classified drivetrain produces a measurable system-level efficiency advantage beyond what the hub efficiency figure alone suggests.
This animation shows the internal kinematics of the hub in both ratios — the component that makes all of that possible from inside a small cylindrical package at the center of the rear wheel.