Many power meters calculate power on the basis of the average angular velocity (or cadence) per pedal revolution, as if the pedaling were always perfectly smooth and uniform. In this article, we will see how this approximation can heavily impact the accuracy of the measured power data, especially when using oval chain rings.
We will also see how systems based on Instantaneous Angular Velocity, such as IAV Power, can guarantee and maintain the highest degree of accuracy even where others fail.
Basics: how does a common power meter work?
High-precision power meters for cycling are positioned on rotating parts of the bicycle (pedals, crank arms, hub, spider, etc.) and, regardless of technical and construction differences, all perform the calculation of power on the basis of two quantities: force and angular velocity.
Both the force and the angular velocity components are not constant, but instead vary continuously within the same pedal revolution.
The variations, which can also be very significant, depend on various factors, such as the cyclist’s pedaling style and athletic preparation, the type of chain ring used, the slope of the ground, the model of roller used, etc.
Therefore, to guarantee the maximum degree of accuracy in any situation, the calculation of the power generated in a pedal revolution should take into account the variations of both force AND angular velocity.
Generally, power meters detect the variation of force through appropriate sensors (e.g. strain gauges); which allow the force to be measured hundreds of times per second during the entire rotation. The values measured are called samples.
On the other hand, the variation of angular velocity seems to be commonly neglected, i.e. it is not sampled. Many power meters use the average angular velocity of the revolution instead of the real instantaneous value.
This, however, introduces an unforeseeable error into the power calculation.
Where do some power meters go wrong?
Using the average value (Average) of the angular velocity, instead of its instantaneous form (Real), means considering each pedal stroke as perfectly smooth and uniform: this type of pedal stroke does not exist in reality.
Favero Electronics research (access to research material) has clearly shown that the failure to consider changes in angular velocity has a negative impact on the accuracy of power meters in any pedaling situation, especially when using oval chain rings. In the paper analyzing the "Influence of Angular Velocity of Pedaling on the Accuracy of the Measurement of Cyclist Power" you can easily see how a power measurement system that does not detect instantaneous angular velocity introduces an error that can reach 4.5%.
What are the advantages of IAV Power?
The IAV Power system is Assioma’s new power calculation system based on the realinstantaneous angular velocity.
Thanks to proprietary software solutions, Assioma fully exploits the potential of the integrated three-axis gyroscope, detecting the real trend of the angular velocity, with its variations, and integrating it into the calculation of power. Not only does this increase overall accuracy to ±1% but it also guarantees it in real pedaling conditions. Not just in laboratory tests.
Here are some of the most common situations in which the IAV Power system proves its relevance:
Piston-like pedaling: especially uphill with steep slopes, standing or sitting, cyclists tend to give very irregular pedal strokes with very pronounced variations in angular velocity.
On a bike trainer: each training roller has a braking system to recreate the right experience for cyclists. This system changes from model to model, and since the inertia produced impacts directly on the angular velocity of the pedal stroke, there is an immediate influence on the expression of power.
With non-circular chain rings: oval or elliptical chain rings are designed to take advantage of the pseudo-sinusoidal course of the pedaling torque. In these cases, it is essential to have a power meter capable of instantaneously detecting angular velocity, because variations in this velocity are not only inevitable, but even mechanically accentuated.
The new IAV Power system by Assioma was created to meet actual cyclist needs and was not only inspired, but also implemented thanks to the continuous feedback of cyclists and triathletes who have already chosen us. The IAV Power system is just the latest of many unique solutions resulting from this valuable exchange of experience, yours and ours. To discover other features and strengths of Assioma, see also