I don’t think that’s the case. The difficulty in a power meter is to calculate the load normal to the crankarm line, and eliminate the flexion/compression alongside the arm. While that’s easy for a set of strain gauges on a straight beam, it becomes a lot more difficult when dealing with a hollow part with a complex shape and integrated chainring attachment points like the recent Shimano crankset. So the errors come from the incorrect separation of pedaling forces between contributing (i.e. normal to the arm) and non-contributing (alongside the arm). The distribution of these two components changes quite a lot between riders, cadence ranges, and standing vs seating pedaling.
I mean, it is, you are describing it in the following sentences. We use strain gauges in yachts that are worlds more complex than a simple power meter. But the properties and flexion/deformation across any load profile are very precise and known in advance.
At any rate, this probable could use it’s own thread.
Can we move the crank discussion to a separate thread and keep this to the original topic?
I can push them into a new thread, or leave that to someone else to start, and I can migrate the related posts as needed.
I’m done anyway.
It is certainly not impossible to build accurate power meters with asymmetric crank arms, but it seems impossible to reach the claimed accuracy when manufactured at scale. When even manufacturing tolerances that would otherwise be considered small make it difficult to produce accurate power meters at scale, the fault lies with the design.
This is further evidenced by the fact that according to @gplama’s testing all Shimano-based right side power
meters suffer from the same inaccuracies.
I don’t think this is correct: the properties of carbon are highly anisotropic, so properties like stiffness depend crucially on the layup (type of carbon, direction of the weave, etc. etc.). The same can’t be said for isotropic materials like aluminum.
Moreover, if it were the material, then the left side should also be inaccurate — which from what we know it isn’t.
Again, that crank talk belongs in a separate thread.
Upon 2nd look, the OP is the only real OT post, so might as well let this be the crank topic, I guess.