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Trail arises out of the steering axis angle and hub offset from the axis, it doesn't matter whether that comes from a head tube and fork or a king pin. It is actually possible to ride a single track vehicle with zero trail, the monkey on top being surprising adaptable to less than ideal chassis design.

i understand that bro, but it's the change in trail as you turn the bars that's relied on. The offset effectively decreases as you turn, and as you lean into a turn, it tends to pull the wheel into the turn. this is why you can ride with no hands, I suppose you could have a virtual axis angle about which the "offset" rotated, but i don't see that being discussed, nor can i imagine a simple way in which to design it because the offset would have to be nearly as large as the radius of the wheel.

As for a monkey do, the difficulty riding unicycle isn't the forward and backwards aspect, its staying up laterally thats difficult. Why? no trail, and you cant turn by simply leaning into the direction you want to go. You can, but you have to work hard to compensate else you fall into the turn.

my understanding at least.