I unsuccessfully built something like this for my bicycle a while back: https://niels-ole.com/bike/maker/2020/02/20/bicycle-light

> It turned out that when I accelerate strongly, I pull the bike back, at some point in the rotation of the pedals. This is rightfully detected as a sudden deceleration of the bicycle.

I guess on a much heavier motorcycle the deceleration of the motorcycle is actually a meaningful indicator of the combination driver+motorcycle slowing down.