After previewing an early prototype at last year’s Eurobike show, Rotor this year unveiled a more production-ready version of its new crankarm-based power meter. It legitimately looks to offer a number of competitive advantages over current offerings.
It’s also competitively priced at €1,690 (about US$2,000), impressively light at 556g (claimed, without bottom bracket or chainrings) and will supposedly be available before the end of the year.
Unlike most systems that essentially provide a single device to measure power output, the Rotor Power is essentially two meters in one, with each of the crankarms housing four strain gages and their own compact plastic housings containing the batteries, transmitters and other ancillary electronics.
Despite this redundancy, Rotor claims just a 30g weight penalty over its standard 3D+ MAS model. Claimed weight for a complete Rotor Power – without chainrings or bottom bracket – is 556g.
How is it different?
Having one complete power meter per side affords obvious analytical advantages over single-meter systems. Instead of averaging left and right power to produce a single composite value, Rotor says the Power will display left and right leg outputs in real time with a compatible computer head (currently, Garmin’s Edge 500 and 800 are up to date).
Rotor rightfully touts the Power’s unusually high, 500Hz sampling rate, which works with the built-in firmware to provide two additional efficiency-related metrics. According to Rotor’s Christie O’Hara, these include torque efficiency – a measure of the positive vs negative torque per leg – and pedal smoothness, which is analogous to Computrainer’s SpinScan function and provides an indication of how evenly you apply power throughout the crankarm rotation.
Both functions will be accessible via Rotor’s proprietary desktop software, but newer Garmin Edge computers will apparently be adding the torque efficiency figure to the display with a future update.
Tacking the extra electronics packages onto the ends of the crankarms thankfully doesn’t affect the pedal stance width or ankle clearance: James Huang/Future Publishing
Having the electronics package on the crankarm ends doesn’t affect ankle clearance
Despite the high sampling rate, Rotor nevertheless insists that abnormal power output spikes such as shifting and rough roads are automatically filtered out of the display.
Claimed accuracy is +/- 2 percent, although Rotor says internal tests are regularly within +/- 0.5 percent. More importantly, though, Rotor Power designer Antonio Brivio claims the arm isn’t sensitive to variations in temperature and has to be ‘zeroed out’ only after a hardware change. In other words, once you install the Rotor Power and do the initial calibration, it doesn’t need to be regularly calibrated again provided you don’t swap out chainrings – at least in theory.
Other plus points
Rotor has even paid some attention to the unit’s durability and compatibility. Claimed battery life is 300 hours, despite the high sampling rate, and the batteries are user replaceable.
In addition to being compatible with any power-equipped ANT+ computer, the crank’s firmware can be updated via the same wireless protocol.
The new rotor power cranks are based on the company’s existing 3d+ crankarms. the strain gages are glued inside the existing channels and the electronics are attached to the end of each arm: James Huang/Future Publishing
The new Rotor Power cranks are based on the brand’s existing 3D+ crankarms
Finally, Rotor will build the Power exclusively in its 30mm-diameter ‘Universal Bottom Bracket’ axle fitment, which is similar – but not identical – to the BB386 EVO standard introduced by FSA last year.
That being said, Rotor says its UBB-standard Power cranks will fit into virtually any bottom bracket shell, barring the Trek Madone’s, with its drop-in bearing design. Rotor will also produce the Power cranks in a mountain bike version, but only in a two-ring configuration for now.
Rotor promises availability on the new Power cranks by Christmas 2012, and the suggested retail price is €1,690 (roughly US$2,000).