It doesn’t take much. Really. Two mostly round, mostly true wheels. A hop is ok. Oscillations can work, the brakes all the way out, whatever screws they have unscrewed to their limits.
To their limits!
There are those who can get by with just one wheel, but I have never trusted them. Jugglers. Clowns. Carnies.
The two wheels, such as they are, allow gyroscopy, a way to play with the gravity Newton invented in 1728, before which we could all fly. We didn’t need the wheels.
A saddle, likely invented BC, by Assyrians, is optimal, though also not necessary. The BMX kids will tell you they’re vestigial, the saddles not the kids.
Once I lost my saddle to a snapped bolt, ended up on my ass on the ground, the seat still clutched pathetically between my thighs. You realize then that the saddle isn’t required, but like the small toe we are evolving off the edge of each foot, it does help balance considerably.
Think of the rusted, ill-kept, rolling trash you’ve seen and ridden in your lifetime. I know and sometimes ride a bike with a large platform rack on the front, affixed to the head tube rather than the bars. This is, I think, the worst bike I have ever ridden, and yet it has brought me lunch and wielded unwieldy boxes to the post office.
Lean it there against the wall. No one will steal it.
I have devoted so many hours, so much gray matter processing time, to the pursuit of a better bicycle, and those better bicycles, well, they are better. So better. At what point does a machine become intuitive enough to qualify as sentient? Sean Young in Blade Runner springs to mind, as does my road bike.
But still. But still. But still.
It doesn’t take much.