Pedal or crank power meter?
If you want to change your power meter frequently between bikes, there is no getting round pedal power meters, which have also proven to be very robust in endurance tests (Favero). In principle, we can attest to the very good accuracy of all current pedal power meters.
Measure on one or both sides?
On both sides! Admittedly, the offers for one-sided measurement are attractively priced. But the accuracy suffers considerably. Measured on one side, +/- 1.5 per cent accuracy quickly degenerates to +/-5 per cent in the display with an assumed left-right force distribution of 48 to 52 per cent, which is quite typical. A deviation of 20 watts is quickly possible. In addition, the power difference between the legs is not necessarily constant. It can happen that the right-left balance is reversed at high power levels compared to low ones. If you measure, then do so as accurately as possible, otherwise sooner or later big question marks will appear.
Real measurement on both sides?
Only dual crank or pedal power meters provide an exact resolution for left and right legs. With the classic measurement in the crank star, the total is recorded correctly, but the left-right display is inaccurate, as it is unclear what contribution the legs make in the pulling phase.
Built-in rechargeable battery or exchangeable battery?
Nothing happens without power. The power meters are either powered by an internal rechargeable battery or replaceable batteries. The advantage of the permanently installed battery: greater reliability and better water resistance. Battery contacts are always a source of error, and the covers and screw connections are mechanical sources of error. However, if the battery is defective, the device must be sent in.
Compatibility of the power meters?
Only pedals are fully compatible with all bikes; washers may only need to be fitted if the cranks require this or the axle is too close to the frame. With crank power meters, however, the bottom bracket type and possibly also the space between the chainstay and sensor housing must be taken into account; this applies in particular to the Stages design with boxes on the back of the crank. Otherwise, most but not all frames are compatible.
Is absolute accuracy important?
Yes, initially it may be enough if the data is at least reproducible - i.e. if the same mistake is always made in the event of an error, so that relative differences become visible through training. But in the long term, only accurate data is valuable. Sooner or later there comes a point where the absolute value becomes interesting, for example when you compare yourself with other athletes or when other devices come into play. Unfortunately, dubious values are then of little value. They cause confusion and uncertainty and thus devalue the measurement.
Does your own power meter show correct values?
The best way to find out is to compare it with other power meters. This also includes smart trainers. These are not the most accurate devices in absolute terms, but they do show a trend. The display of the power meter on the bike should always be a few watts above the value of the Smarttrainer, as the chain transmits the power to the rear with a slight loss of around two per cent. The best comparison is made in ergometer mode with watt preselection. The best way is to compare it with other power meters on the bike - as in the TOUR test. Steep hills where the wind has as little influence as possible on the ride or measurement are ideal for recalculating. Using the total weight, the riding time and the metres of altitude climbed, the uphill performance can be checked relatively easily by calculation - to an accuracy of around two percent.
The benefits of power meters?
A typical application of power meters in amateur sports is the correct categorisation of performance on long distances - as in the picture above for the Dolomite Marathon. The power meter helps you not to set off too fast at the start. Over the entire distance, however, the power output drops slightly. The curves in detail mean Power (yellow), heart rate (red), speed (green) and cadence (turquoise).
