Test: The Spanish company Rotor presents a power meter that provides various clever features at an attractive price, is relatively easy to install and looks stylish and unobtrusive on the bike.
Power meters are no longer just something for professional cyclists or ambitious amateurs. An SRM on the bike still likes it Taj status symbol of the young amateur, but alongside the expensive pioneer, various manufacturers have emerged that enable serious performance measurement at affordable prices. One of them is Rotor, the Spanish company that years ago competed with a practical chain catcher and presented a complete hydraulic groupset for the first time at the Eurobike. Of course, the Spaniards are known for their light aluminum crank sets, which are also available with integrated power measurement.
It started with the Power model, which provided a separate measurement for each leg; this was followed by the Power LT with only left-sided measurement at a lower price. Now, with the InPower, a third model has come onto the market, which could become a blockbuster given its low price: The system is available from 649 euros, whereby this offer is aimed at cyclists who already have a Rotor crankset on their bike. Because in the basic version there is only the left crank with attached shaft, on which you can mount an existing right rotor crank.
We received a complete crank set for testing - the very light 3D+ version with a weight of 530 grams for the shaft and both cranks without chainrings and bottom bracket, which costs 899 euros. If you open the box with the shapely aluminum cranks, you have to look closely to find a reference to the measuring electronics, which were developed in cooperation with the Spanish technology group Indra: Aha, there is a small one on the left crank arm Extension made of plastic, also you can not see through the 30 mm shaft as usual - on the left there is a flap that is turned to open, on the right behind the thread for the crank screw is a small cover. This suggests the solution to the riddle: The sensors are located in the bottom bracket shaft, whose torsion is measured; The determined data is sent to the bike computer via ANT+. And since the system also includes an accelerometer, there is no need for magnets to record the cadence - more than the slightly differently shaped left crank is not visible.
Compatible with all bottom bracket standards
When looking at the 30 mm shaft, there is a moment of uncertainty: Hmm, what kind of bottom bracket standard does the frame have to have in order for this thing to fit? It doesn't matter - Rotor has bottom brackets for every frame, even for those that still require screwed bearing shells (BSA/ITA thread). So we order a BSA bottom bracket from the UBB range, which is permanently mounted in the frame. Now the crank is pushed in (the clamping ring eliminates any axial play), the right crank is screwed on with our chainrings - done.
However, something is still missing to turn the crankset into a power meter – a power source. This is where the aforementioned flap comes into play: behind it is a slot that a conventional AA battery is inserted into. This is extremely practical, because it saves expensive button cells that are difficult to insert and which, moreover, are not available everywhere. AA batteries, on the other hand, are stocked at every gas station. The flap is sealed and greased with an O-ring and closes very tightly, so it should be permanently watertight.
Quick and easy calibration
To display the measurement data, we use a Garmin Edge 1000, which is a good choice for power meter users with its high-quality screen, clear menu navigation and individually configurable display. The Rotor system is immediately recognized by the Garmin after it has been activated by a few turns of the crank. Calibration is also easy: the left crank arm must point vertically downwards; then touch the Calibrate button on the touchscreen. As soon as the value 1000 is displayed, turn the cranks backwards a few times, put the left pedal down again vertically and repeat the procedure. If a value between plus and minus 200 is now displayed, it worked and the system is ready to go. Don't forget to enter the crank length that is needed to calculate the torque.
That a power meter is a useful thing becomes clear after the first few kilometers. The average cyclist quickly realizes that he is basically constantly on the move in a complete mess of the training areas. The short, steep ascent after a few minutes of easy rolling is already completed in the top area; After that, it only works in the lower GA-1 range. Once you've regained your composure, you'll find that the performance increases steeply even with minimal waves, only to then drop sharply - a real yo-yo effect that occurs when you try to ride an even pace. It's even more extreme on longer climbs and descents: the former is almost exclusively used in the development and peak area; the latter cannot even be described as training, especially since you can't put 100 watts on the pedals for miles despite hard pedaling.
Training with power measurement ensures a more considered driving style
Anyone who listens carefully to himself may also gain this knowledge roughly through his body feeling. However, the feeling of stress often occurs with a time lag to the performance and sometimes even has nothing to do with it. Example of pedaling frequency: Increasing from the usual 90 revolutions at the same speed to a frequency of 100 feels a lot more strenuous, despite the same performance, because the strain on the cardiovascular system is greater - and thus the training effect.
Training with the InPower quickly leads to a more considered driving style - which is particularly helpful for amateur athletes who often train too intensively. Anyone who dares to take the step to really systematic training from here cannot avoid performance diagnostics. A 20-minute test on the road can serve as a preliminary stage, in which you give everything - but not too early, so that you can still improve towards the end. Based on the average performance (minus 5%), various online calculators determine the individual training areas; How to make the best of this knowledge is explained by professional training institutes, such as KOM*Sport in Cologne, where we received detailed advice on the subject of performance measurement.
There we also checked the accuracy of our rotor system on a scientific Cyclus 2 ergometer. In a 10-minute test with an average power of 200 watts and three minutes measured separately at 350 watts, the InPower showed a consistent deviation of +5%. These are probably due in equal parts to the unavoidable measurement tolerances and the efficiency of the chain drive, which consumes two or more percent of the power depending on the maintenance status. Incidentally, with these values, the InPower crank is at the level of various other power meters.
Rotor offers an extensive software package for its system, which is used less for evaluating the data than for setting up the measuring crank and uploading new software. Since the InPower measures on one side on the left, it can make sense to adjust the factor by which the power of the left leg is multiplied if there are strong muscular differences between the left and right leg. However, measurements taken with a driver who had significantly less strength in his right leg after knee surgery (clearly visible in the smaller thigh circumference) showed that this right/left balance is less important than is generally assumed. In tests with different power measurement pedals, sometimes the left leg was rated more heavily, sometimes the right one, and even then the deviations were small - 52 to 48% and 47 to 53%. With measuring pedals or cranks that measure the power of each leg individually, the risk of measuring tolerances influencing the values is of course doubled.
For optimal alignment of Q-Rings
A very interesting feature of the Rotor software is aimed at users of the in-house asymmetrical chainrings, called Q-Rings. The electronics of the InPower measure at which point of the pedal rotation the applied torque is greatest, which is displayed graphically by the analysis software. This information can be used to optimally align the Q-Rings without having to experiment for a long time.
Conclusion
After a number of rides and indoor tests with the Rotor InPower, our conclusion is clear: When looking for a suitable power meter, the Rotor InPower should definitely be on the short list. In addition to the low price and the high level of accuracy, features such as the inconspicuous integration of the sensors, the power supply via AA battery and the absence of spoke magnets, etc. are also appealing. If you own several bikes with rotor cranksets, you can easily switch the power meter between them - from training to competition bikes and in winter to cyclocross bikes. And anyway: If you want to cycle faster and have a few hundred euros left over, you shouldn’t invest them in a new aero wheelset or light carbon parts anyway, but in a power meter – maybe the Rotor InPower.