[abakker]

OK - this is probably my ignorance talking, but why is it surprising that bike are balanced? The pedals are basically shoulder width and staggered, which is a very natural position for people to balance in as bipedal creatures? in addition, while the bike is moving, won't the inertia tend to keep things moving in the same direction?

This is all coupled by the fact that the rider is actively piloting and adjusting the bike to keep it under control at all times. The bike seems like it would balance to me because the control mechanisms are designed to keep things balanced easily.

[Someone]

Bikes balance themselves; they don't need a rider to do it for them. Watch https://www.youtube.com/watch?v=oZAc5t2lkvo

[HCIdivision17]

I just want to note that this also happens on motorcycles. On a cold winter day my bike dumped me off as I lost traction at a stop light. It started to fall over, bumped its saddle bags, and before the tilt sensor could stall the engine it righted itself in second gear and idled its way through the intersection... with me literally running after it. It hit a curb and eventually stalled upright.

Second most embarassing thing the bike ever did to me.

[sohkamyung]

Dare I ask what was the most embarrassing thing the bike did to you?...};-)

[HCIdivision17]

Oh that was at a stop light shortly after it started raining in a Texas winter. I'm fully layered and geared up with leathers and full rain suit - I can walk a bit like a robot and look 150 pounds heavier. So I pull up to the light and just before I fully stop, my Dyna just ... slides out from under me. It's rush hour, a busy intersection, and my bike just sorta falls over in place while I'm sitting on it. Nothing you can do can stop it once it slowly starts properly tipping over, so it plonks onto the roll bars and bags (which are wide and leather, thank god). I scramble to haul it back upright on this oil slicked crowned lane, hop back on, and act like nothing at all happened.

[nathanielc]

Bike are balanced and symmetric side-to-side. Top to bottom they are not, obviously. The center of mass is above the ground , so a bike that is not moving will fall over to lower its center of mass. But this doesn't happen if the bike is moving. Push a bike without a rider and it will travel for a few feet without falling over, and take longer to fall over if just left standing still.

[Someone]

The surprising thing is that it is way more than "a few feet". Apologies for repeating myself, but watch https://www.youtube.com/watch?v=oZAc5t2lkvo (And that is not on smooth terrain)

And nitpick: typical bicycles aren't symmetric left-right. The chain and gears make them heavier at the right. Most mass is close to the center line, though, so its moment is negligible, especially when ridden by a human.

[malz]

It's surprising to the extent that: balancing on a non-moving bicycle is hard. Riding a unicycle is hard. Riding a bike is easy.

[jackmott]

bikes are balanced without a person on them