The new Power2max power meter offers the principle of the market leader SRM at a competitive price: Saxonar, a company from Waldhufen in Saxony that specialises in wireless data technology, charges 690 euros for the sensor and from 890 euros with cranks (without chainrings). SRM's system is around three times as expensive in a comparable design. Saxonar uses strain gauges to measure the torque transmitted from the bottom bracket shaft to the chainrings in the replaceable crank spider. The principle is copied from SRM, whose patent has expired. The electronics are waterproof and solidly encapsulated in plastic. The system cannot be repaired, but firmware updates and calibrations can be carried out at the factory. The battery is easily accessible from the outside - a plus compared to SRM, which has to be sent in for battery replacement (and recalibration after prolonged use). Saxonar claims that recalibration is not necessary even after a long period of use. The battery is said to last 300 to 400 hours. An acceleration sensor integrated into the crank spider records the cadence, which greatly simplifies assembly and eliminates a potential source of error.
Variety of connections
The sensor's radio signals can be received by computers that work with the ANT+ standard (Garmin, o-synce, etc.). Saxonar does not build its own computer. Compatible cranks come from SRAM, Rotor and TA. Crank spiders for compact or standard blades are available, BB30 bearings for SRAM and Rotor should be available soon.
For the test, we fitted a 3D rotor crank with round SRAM blades and an Edge 500 computer from Garmin. To compare the values, we used a tried and tested PowerTap hub, whose data was saved by a second computer. Apart from rounding differences in the display, the devices are very synchronised. Whether continuous load or sprint peaks - the power display differs by 1.3 to 2 per cent. The slightly lower values of PowerTap compared to Power2max can be explained by friction losses in the drivetrain. Saxonar states an accuracy of +/-2 per cent. However, our tests indicate that the accuracy is even higher. The automatic calibration of the zero point (which is temperature-dependent) is super. The device calibrates itself automatically - whenever the crank stops after at least five rotations. This works, as confirmed by our test in which the crank sensor was cooled down to -5 degrees and then used at room temperature. Short pedalling breaks were enough for the device to compensate for the temperature stresses. As with SRM, Power- 2max also offers professional users the option of checking the calibration using test weights. Minus point: In three out of five tests on the roller, the power display switched off a total of five times, lasting between a few seconds and a minute. It is unclear whether the sensor or receiver is responsible for this. When asked, Saxonar considers interference with other radio sources such as WLAN to be possible. The Power- 2max power meter is inexpensive and easy to use. The measuring concept, accuracy and good workmanship are pleasing. Some details are even better than with SRM. However, the dropouts during roller training raise questions. A long-term test will have to show how reliable and durable the device is.
- Weight rotor 3D crank with sensor, 172.5 mm without bearing, 53/39 t: 882 grams
- Price incl. Rotor cranks, without chainrings: 990 euros
- Sensor alone 271 grams, 690 euros
- Reference/Info www.power2max.de
Text and photo: Robert Kühnen
