ROTOR manufactures an axle-based power meter called the INpower. The ROTOR INpower places its 4 strain gauges inside the axle (hence the name ‘INpower’). The INpower uses ROTOR’s 30 mm UBB (Universal Bottom Bracket) design which allows ROTOR to use the same power meter with both their road and MTB cranks. Another advantage to the axle-based design is that it means the critical components of the power meter are safe from impact, dirt and water. The INpower is available for MTB, road and triathlon/TT.
The INpower can be purchased as a complete crankset, or as a left arm only option. The latter option is convenient for cyclists who already own a current set of ROTOR cranks and can therefore purchase a left arm only power meter, enabling them to simply swap out their current left arm for the new, power-equipped one.
The weight of the ROTOR INpower 3D+ crankset is 525 grams in a 110 BCD, 170 mm crank arm configuration. As we always say, when considering weight, be sure to take into account the weight of the component(s) you are replacing. 500 grams might sound like a lot, but if your existing crank weighs 400, you’re only adding 100 grams.
Left/Right Power Measurement
The ROTOR INpower 3D+ does not provide left/right power measurement.
The INpower runs off of a single, AA battery. The use of AA batteries is welcomed as they are readily available and easy to find.
The ROTOR INpower has a battery life of approximately 300 hours – pretty close to the average for most power meters currently on the market.
The INpower features a low battery message. When the battery is near the end of its life, the INpower cranks will send a message to your head unit, letting you know the battery is getting low.
Difficulty to Change
The battery is very easy to change on the ROTOR INpower 3D+, and can be accessed by removing a cap on the side of the crank arm. No special tools or tricks needed.
The ROTOR INpower transmits data via the ANT+ wireless protocol, and is therefore compatible with any head unit that supports ANT+. Note that in order to display TORQUE 360 and OCA values, the user’s head unit must support this data. The majority of today’s head units should work fine.
The ROTOR INpower 3D+ utilizes an accelerometer to measure cadence. The advantage to an accelerometer is that you don’t have to worry about gluing a magnet to your bike (the other way power meters detect cadence is with a magnet and reed switch).
As soon as you start riding, or apply any force to the non-drive side crank, the INpower will wake up. To calibrate, place the left crank at a 6 o´clock vertical position and without any weight on the pedals, perform a calibration using your head unit. The calibration value should show “1000”. After you see 1000 appear on the screen slowly turn the crank counterclockwise two or three turns and place it in a 6 o’clock vertical position again. Calibrate once again and record the offset value shown in the monitor. You can repeat the process if necessary to ensure numbers are in the same range.
The INpower does not need to be calibrated before every ride, but rather after installing the power meter or changing any drivetrain componentry (pedals, chainrings, etc.). After the initial calibration, it is recommended you calibrate a second time after 30 hours of riding.
ROTOR provides two years of warranty for all its products.
ROTOR is known for their oval shaped Q-Rings so it was critical that their power meter be Q-Ring compatible. To this end, INpower features TORQUE 360 and Optimum Chainring Angle (OCA) pedal analysis, which helps cyclists assess force variations in their pedal stroke. TORQUE 360 and OCA values enable cyclists to orient their Q-Rings around their distinct pedaling characteristics in order to take advantage of their most productive zone. Note that since the INpower cranks have the same BCD as standard cranks, you can also use them with any compatible round chainrings. Being able to run oval shaped rings is a distinct feature of the ROTOR INpower. In fact, other than ROTOR, only PowerTap’s hub-based power meter has been proven to support oval rings.
ROTOR offers their MAS spider as an option with select ROTOR power meters – such as the INpower and 2INpower. MAS stands for Micro Adjust Spider. The ROTOR MAS spider allows you to fine-tune your Q-Ring position to better suit your needs and pedaling style. ROTOR calls this the Optimum Chainring Position (OCP).
For example, using a standard spider and ROTOR Q-Ring, you typically have approximately 5 degrees of adjustment. The MAS spider has additional bolt hole options, effectively giving you half positions or approximately 2.5 degrees of adjustment.
In addition, there is no additional weight penalty when using the MAS spider.
INpower Power Meter Options
ROTOR offers several options of the INpower for both road and MTB. For the road, they offer the FLOW, 3D+ and 3D30. You can choose to buy the full crankset, or just the left arm at a lower price. For MTB, they offer REX 1 and REX 2. Again, you can choose to buy the full crankset, or just the left arm. Note also that with the MTB versions, if you buy the full crankset, you have your choice of a 1x or 2x chainring set up. For example, the REX 1.1 is the 1x, and the REX 1.2 is the 2x configuration. Here are some charts that brake down your options.