Bicycles and Cats, and why bicycles self-steer themselves (and cats always land on their feet)

I’m curious, how does stem length impact steering feel?

I realize that steering feel is almost 100% impacted by trail (how far the contact patch is behind the line of the head tube) but for example, on my project bike, the old quill stem is 70mm, which puts the handlebars (3 inches) behind the hub; the new quill stem is 150mm which should put it in line with the hub.

I was looking in to wheel trail and came across this experiment again on bicycle stability, but apparently now there’s a Wikipedia page on it, and also a very good video with description of how it works (the wiki page sucks). Basically the idea is to remove things like gyroscopic forces (wheel stability), trail (front wheel auto-stabilization) and see if the bike will keep going in a straight line.

Basically what they decided is that since the front wheel has a non-zero mass, since the fork/wheel is smaller it actually rotates at a faster rate than the rest of the frame. As a result the steering motion causes the bike to self-right despite the fact that it has negative trail.

Ok, so what does that mean exactly? Well fortunately someone as smart as me already went ahead and put this in to a visual frame of reference. With Cats. The internet loves cats. How cats rotate from upside down to right side up in free fall is an interesting part of Physics minutia, but basically the long and short is that once the cat knows what way is up, they pull in their legs in the front and twist, then extend the front legs, retract the rear legs and twist again. Boom, instant reorientation using two sets of angular momentum. That probably made no sense so here’s the video.

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