Not all Power Meters are born equal

There is an incredible array of Power Meters on the market Power Meters in the rear hub, in the pedals, on the left arm of Crankset, in the Crankset axle Crankset even directly on the drive base. Such variety produces... varied results.

As you might expect, the power generated under your feet is not the same as that under your tires. Manufacturers must therefore find a way to standardize measurements in order to adapt their technology to the power that cyclists actually generate. Even though they are doing everything they can to produce reliable sensors, it is no easy task.

How does a power meter work?

Let's start with the basics. A Power Meter a device that measures the torque applied by the cyclist and their angular velocity (RPM). The most common technology is the use of a strain gauge installed on a deformable material (often aluminum). The strain gauge is connected to an accelerometer, which is used to determine the number of pedal revolutions you make. These two components are housed in a fairly compact space and are usually accompanied by a battery and an electronic card that is used to communicate with the graphic display (computer, screen, Garmin, etc.).

• The strain gauge is attached to the deformable material. When deformation occurs, the resistance in the gauge changes and a relationship is established between this deformation and the elastic constant of the material. In short, torque is detected.

• The accelerometer is integrated onto an electronic board and detects acceleration in different axes; it returns a cadence in RPM. Note: some manufacturers still use a magnet system to measure the number of revolutions made by a crank. This technology does not use an accelerometer.

• The electronic card sends waves to a receiver usually placed on the cyclist's handlebars. Some sensors are compatible with phones (via Bluetooth, for example). The most popular communication mode currently is the ANT+ protocol. The data is processed by the computer and not by the Power Meter.

• The battery is the heart of Power Meter. It powers the entire system. A low battery can send incorrect or erratic readings to your computer.

Why don't all power meters read the same?

Knowing what's inside a Power Meter, it's easy to understand that a wide range of variables come into play in the assembly, calibration, and use of these devices.

Strain gauges, for example, are extremely sensitive to temperature changes and can provide inconsistent data when such variations occur between calibrations. Accelerometers can also give incomprehensible readings during jumps or when the Crankset a rock.

Power Meters also Power Meters varying degrees of accuracy. This is specified by the manufacturer. Stages, for example, have an accuracy of +/-1.5%. This represents a difference of +/-5 watts during a 300-watt effort. Thus, for the same calibration under similar conditions, two sensors receiving 300 W of power may have readings of 295 W or 305 W. This is a fairly significant difference.

Comparison table of different models and their accuracy

Parmi contributing to the disparity in power between sensors Parmi their location (wheel, pedal, training base), how the calculation algorithm is managed, and how you use the device.

I can confirm that a wheel sensor and a Crankset sensor Crankset give the same power output. However, it is difficult to determine which one is correct. Parmi many devices I have owned over the past few seasons, I had my favorites (the ones that gave me watts), while others I liked less (the ones that stole watts from me). The fact remains that I still don't know which figures were correct...

How to stack the odds in your favor

To ensure accuracy and, above all, consistency, it is important to calibrate your Power Meter regularly. Do this when you start your workout so that the device has time to acclimatize to the surrounding conditions. For example, if you calibrate your power meter outdoors at -14°F and then train indoors at 77°F, the readings may be inaccurate.

Remember also that you should not rely entirely on your Power Meter, nor think that the watts are absolute. Trust your own figures. By always using the same type of Power Meter, you will be able to see your progress and notice trends in your training. Conversely, if you change devices, don't get too excited if you break power records...