HerrKaLeun

Nice Video explaining the theory

Mark VerMurlen

clengman

Obviously, this is a bunch of malarkey. Bicycles are stable because God made them that way because he wants his children to be happy!

(But seriously, that was a really cool talk. I wish I knew about that guy when I was looking for grad school programs)

indyfabz

Genius

Brocephus

When I was a little kid, and we'd visit my grandparents, there was an old Schwinn (IIRC) down in the basement that I'd ride with the local kids when we were visiting. One time when we were flying down this long,steep hill that's a block behind my grandparents house, the chain came off and I couldn't stop. I was approaching a stop sign and intersection, so I somehow managed to jump off the bike onto the grass. After i tumbled to a stop I saw the bike keep going, straight through the intersection, then into the woods, and down into a small ravine with a creek in it. I was always baffled at how the bike keep riding itself, especially after what I always recalled as fairly considerable lateral force of me jumping off the top tube (though not in those terms, at the time, LOL!).

Shimagnolo

I was afraid this was going to be a rehash of the gyroscopic theory.
But what a pleasant surprise!!!
This video is a must-see for anyone interested in bicycles!

Daniel4

The unicycle is light and maneuverable. But it's not stable. A lot of them are fixies. There's a video showing a unicycle with freewheel but I'm guessing you'd need a lot more skill just to stay up-right on one of those than on a fixie unicycle.

Three wheels is a tricycle but they are heavy and slow and I suppose not very maneuverable.

But the two wheeler is light, manueuverable and stable. Since both wheels are in the same plane and rotating in the same direction, it would take a bit of force to flop it over. Moreover, if the bike does want to flop over, the front wheel inherently turns to make the falling motion into a forward rolling motion - at least until all the angular momentum is gone.

bicyclridr4life

Not necessarily. Back in the 1950's and 1960's ... maybe even the 1970's there were professional and amateur trike (and bicycle sidecar) races.
Those trikes were anything but slow and heavy. Some of the better ones were under 27 pounds, and were just as fast as the bicycles in the Tour de France.
Trikes can also be maneuverable (at slow speed I can make a "U" turn in it's own length) and they're a blast to ride when you take a corner on two wheels. At least my Miami Sun is. You can also do a seated "track stand" on a trike without holding the handlebar, or having your feet on the pedals. I think that makes them fairly stable.
I can't think of any bicycle that is stable at or below walking speed.

The bicycle I had in college was an old all chrome Firestone(?) Western Auto(?) "Middle Weight" tank bike. Even before I put on the roughly10 pound internal gear 3 speed crank, that bike weighed 65 pounds. I would not exactly call that "light weight". I think a standard Schwinn Collegiate and Suburban were near 40 pounds or more.
Heck, even the Schwinn Stingray and Krates weighed between 45 and 55 pounds, depending on options/accessories.
Yet kids and teens enjoyed and rode the heck out of their Stingrays and Krates or our middle/ heavyweight baloon tired monstrosity now known as a "beach cruiser". I suppose one reason we did was because no one told us we needed an under 18 to 20 pound bike in order to have fun, and we were too stupid to realize we weren't really having fun.

Yes. Some trikes are heavy, and some bicycles weigh less than a butt burp. Regardless of what the bike or trike weighs, they can all be fun to ride.

Joe Bikerider

Shimagnolo

Then I think you will like this one:

Joe Bikerider

Machka 

When I saw "Bicycle Stable", this is what leapt to mind ...