Train and race with accurate, independently-measured power from both legs. The Shimano Ultegra FC-R8100-P integrates dual-sided strain gauges directly into the proven Hollowtech II aluminium crank, giving you genuine left/right power balance without bolting on external sensors. This 172.5 mm version is supplied without chainrings, so you can pair it with the ring combination that suits your riding.

Highlights

• Dual-sided measurement: strain gauges in each arm capture left and right leg output independently for true balance data — no doubled single-side estimates.
• ±2.0% accuracy: active temperature compensation keeps readings consistent as conditions change through a ride.
• 300+ hour battery life: integrated rechargeable lithium-ion battery lets you charge by the week rather than swapping coin cells.
• ANT+ and Bluetooth LE: broadcasts to compatible head units, GPS watches, and training apps simultaneously.
• Hollowglide structure: the HOLLOWGLIDE crank arm design cuts weight while maintaining stiffness, keeping the Ultegra platform fast and responsive under load.
• Without chainrings: 110 mm 4-bolt asymmetric BCD accepts your choice of 2x road chainring combinations.

Accurate power, both sides

Strain gauges built into each crank arm measure force independently, so you see where your watts actually come from rather than a mirrored single-side value. The data includes left/right balance, force vector, and cadence — everything you need to identify asymmetries, track training load, and pace efforts precisely. Zero-offset calibration is quick via your head unit before each ride.

Charge it and forget it

An integrated, fully sealed rechargeable lithium-ion battery delivers over 300 hours of ride time depending on your connectivity settings. Charging is handled via a proprietary magnetic connector, so there are no exposed ports to seal. Most riders will charge once a month or less under typical training use.

Built on Ultegra Hollowtech II

The FC-R8100-P uses the same Hollowtech II aluminium platform as the standard Ultegra crankset. The HOLLOWGLIDE hollow-forged arm structure provides a stiff, light foundation for efficient power transfer and crisp 12-speed front shifting. Power electronics are integrated inside the arms, preserving clean lines and the reliability expected from the R8100 groupset.

Compatibility & Fit

Designed for 2x12-speed Shimano road drivetrains. The 110 mm 4-bolt asymmetric BCD accepts standard Shimano R8100 double chainrings (this unit is supplied without chainrings). The 24 mm Hollowtech II spindle requires a compatible Shimano 24 mm bottom bracket (68/70 mm threaded shell). Chainline 44.5 mm, Q-factor 148 mm. Cadence is measured via a built-in magnet system — no separate magnet required. A minimum 10 mm clearance is needed between the left crank arm and chainstay for sensor installation.