Moving bikes stay upright but not for the reasons we thought

"Most people have seen a gyroscope in action, so the stability of a rapidly rotating wheel should be fairly intuitive, making this a focus from the start. People have built bicycles with counter-rotating wheels and found that they still remain upright, so that can't be all of the story."

Um, counter-rotating wheels are still gyroscopes. In fact they're extremely stable gyroscopes in that they won't impart rotational velocity on the frame. So by having the wheels on a bike rotate oppositely, you're actually making the gyroscopic effect even stronger.

I think Ars is pulling from this article, which isn't about staying upright but is about the self-correcting steering of a bike wheel (i.e. the fact that you can ride hands-free.) http://www.sciencemag.org/content/332/6027/339.abstract -- in which case the conclusion is correct and likely due to the geometry of the wheel. For example tractors have convex pulley systems that allow leather belts to self-center despite not being perfectly aligned. It's counterintuitive but it works.

There's more info at one of the co-authors website: http://bicycle.tudelft.nl/

I submitted this earlier, with the title of the paper, I guess it was too technical to catch people's attention :)

> negligible (4mm) trailing

As you tilt a bike, the effect of trailing on steering increases (i.e. rotational force). This effect is cumulative over time (the velocity of the handlebars turning changes their position in each successive instant; plus the force causes acceleration, increasing the velocity). Small effects become big effects: I would expect that any trailing would induce sufficient steering effects, and so even 4mm trailing is not "negligible".

Hmmm.... you could test this with a "skate bike" - no wheels, just blades on ice, but with a curved front-blade, free to steer, to facilitate "trailing".

But this seems obvious, and it looks like they have been very thorough, so I'm probably missing something (I haven't read their full paper).

* Stabilization occurs because when the front wheel steers that way, it guides the whole bike in a curve, which creates force tilting the bike in the other direction - therefore righting it.

There goes another traditional physics text-book explanation for why things work the way they do.

Somewhat related, Jef Raskin on how the Bernoulli effect is not really what helps create the lift on a plane's wings (as taught by most physics text-books): http://karmak.org/archive/2003/02/coanda_effect.html

Interesting video of a recent WSBK motorcycle staying upright in a crash: http://www.youtube.com/watch?v=Yj9c5poj8Ww

A basic principle of bicycle framebuilding is that if you think you understand bicycle dynamics, you don't. Frame geometries that should ride perfectly develop terrifying handling problems in the metal. Frame designs that are unridable in theory turn out to be relatively practical - perhaps the oddest example of this is the Python recumbent, which steers in the middle, drives at the front and has no handlebars[1]. Bicycles that are self-stable and balance on their own aren't necessarily good to ride and vice versa.

Making sense of bicycle dynamics is particularly bewildering because they are such a natural and direct extension of the rider. Learning to ride a bicycle is a completely subconscious process and what your body is doing runs counter to what your brain thinks is happening. Most people who ride bicycles believe that they steer in the direction of a turn, when in fact the opposite is the case. A child who learns to ride a bicycle with training wheels actually takes longer to learn to ride on two wheels because of this - they have to unlearn steering before they can learn to countersteer.

Bicycles are weird.

[1] http://www.python-lowracer.de/geometry.html

This article had zero scientific conclusions (or in fact any science at all) and the title said "we" in the non-royal sense. Why is this here?

And the article even says they don't know whey a bike stays upright:

"What their math can't apparently tell them is why so many different bike designs tend to stay upright."

To me it sounds like their math is the problem. Its like the bad programmer who blames the compiler for the segfault.

Clearly the universe is fine tuned by an intelligent designer who likes stable bicycles.

Ever since the previous post, I've been wondering where people are getting their bicycles. I've never had a bike that would stay upright on its own at less than ludicrous speed, and the crusty ten speed in the other article had forks that were very obviously bent back, drastically changing the rake and trail.

I also recall an old physics video from High School where the man flipped the fork and handlebars around backwards, specifically so the bicycle would stabilize itself.