Off topic, but does this drive anyone else crazy? Why is changing my route opt out rather than opt in. As far as I can tell there's not even a setting to change that.
I'm with you. There is no setting. This drives me nuts on my motorcycle. I pick the nice scenic route, put the device into my pocket, (Bluetooth speakers in helmet) and then halfway through my very zen ride, this happens and I can do nothing but rage internally and try to remember to pull over and fix it, only for it to happen again 30 minutes later.
Google: you know I'm on a motorcycle. I see that on my location timeline page and marvel at the sophistication of technology. Please for the love of god if you won't give us a simple toggle for this behavior (I know you won't) just take the technology a tiny step farther and don't do this opt-out route changing thing if you detect I'm on a motorcycle.
How does it know you're on a motorcycle? I can imagine that it would be possible to detect fairly reliably with smartphone sensors (correlate curved ground path with gyro tilt), but it's astonishing and frightening that they would put in the effort to go that far.
I think you pretty much described the mechanism there. My friends and I have experimented with "riding like a car" and we can trick the algorithm for short distances if we really think about keeping the phone upright.
The keywords to learn more seem to be "activity recognition API" and I'm pretty sure they have been doing the motorcycle thing for the better part of a decade: