Nobody knows why bicycles don't fall over

[itsbruce]

Apparently, it's a mystery.

[clarion]

Isn't it because of the propstand?

[Hello, I am Bruce]

There's a video of the researchers here, and the paper is here.  They show that gyroscopic effect and positive trail are not necessary for stability (but the trick bike they build to prove it has negative trail instead of zero trail, which might be considered cheating).

[mrcharly-YHT]

Misleading article - it doesn't quite say that it's a mystery, just that there are multiple factors.

Most people can balance a broom on their hand - that's the mechanism for keeping a bike upright. Gyro forces can help - but aren't much of the story.

Confusion of steering stability and 'why don't they fall over' - as acknowledged in the article.

[vorsprung]

Because (despite often being well oiled) they are not drunk

[Rapples]

I know why my bicycles don't fall over






I lean them against the garage wall

IGMC

[clarion]

So that lean to the right meets a solid resistance? 

That's what I like to hear

[itsbruce]

Because (despite often being well oiled) they are not drunk

But they're always tyred, yet they don't fall down.

[Rapples]

Most bicycles prefer to lean to the right.  Those that are leaning to left usually only do so because they are being propped up by using cumbersome flimsy artifical support.  They also often fall over at the slightest touch

[RJ]

There's a video of the researchers here, and the paper is here.  They show that gyroscopic effect and positive trail are not necessary for stability (but the trick bike they build to prove it has negative trail instead of zero trail, which might be considered cheating).

And here's a .pdf ...

(... wot I shall read on the train tomorrow)

[rogerzilla]

I thought it was because of my l33t 5k1lls.

[Regulator]

Well, I suppose somebody had to get a paper published in order to justify their place in the faculty...

[Kim]

It's because when upright the force of the bumble bees colliding with each side is in equilibrium.  As the bike starts to lean, more bees collide with the upward side.  As the bees can't be there (because they're incapable of flight) this creates a pocket of low pressure, so air pressure pushes the bike upright.

As the kinetic energy of an impossible bee is proportional to the square of the relative velocity, the stabilising effect increases with the speed of the bicycle.  At rest, the non-bees are too small to keep the bike upright.

Consequently, a bike cannot self-stabilise in a vacuum, as there would be no air pressure difference, and all the bees would asphyxiate.


_{Time for more codeine...}

[Fab Foodie]

It's because when upright the force of the bumble bees colliding with each side is in equilibrium.  As the bike starts to lean, more bees collide with the upward side.  As the bees can't be there (because they're incapable of flight) this creates a pocket of low pressure, so air pressure pushes the bike upright.

As the kinetic energy of an impossible bee is proportional to the square of the relative velocity, the stabilising effect increases with the speed of the bicycle.  At rest, the non-bees are too small to keep the bike upright.

Consequently, a bike cannot self-stabilise in a vacuum, as there would be no air pressure difference, and all the bees would asphyxiate.


_{Time for more codeine...}

NURSE ... she's at it again ...

[Charlotte]

Kim - have you been at the dried frog pills at all?

[clarion]

Kim explains it all.  SCIENCE ftw.

[Kim]

Kim - have you been at the dried frog pills at all?

*ribbit*

[RJ]

Kim explains it all.  SCIENCE ftw.

Tho' Nature trumps Science  

[Nonsteeler]

Apparently, it's a mystery.

Mr Dave Moulton is also commenting (critically) on that piece, see: Does a riderless bike prove anything? and a sort of follow-up here: More questions than answers

[LittleWheelsandBig]

Mr Dave Moulton is also commenting (critically) on that piece, see: Does a riderless bike prove anything? and a sort of follow-up here: More questions than answers

Dave Moulton was a good framebuilder but is wrong in this instance.

[rogerzilla]

I don't know whether it's possible for an experienced rider to ride a bike with no trail (I expect it is, since even trackstands are possible) but there is certainly a big difference between bikes with lots of trail and those without.  The bike with lots of trail is easy to ride hands-off but is hard to wiggle around potholes.  The bike without much trail (Brompton is a good example, but Thorns also tend to have little trail) can take you by surprise when signalling.  Low trail is sometimes sold as a design "feature" for tandems because the stoker can scratch their bum without making the thing lurch into oncoming traffic.

[Greenbank]

I don't know whether it's possible for an experienced rider to ride a bike with no trail

You can, someone built a bike with no trail and learned to ride it. Proving that it wasn't strictly necessary.

The same researcher also built a bike with a counter-rotating wheel to cancel out the gyroscopic effects. That bike was much easier to learn to ride than the no-trail bike, but still took a bit of getting used to.

It shows that whilst trail, and to a lesser extent gyroscopic forces, aren't strictly necessary they do make significant contributions otherwise it wouldn't be so hard to learn to ride a trick bike with no trail and a counter-rotating wheel. This is quite different from saying that they have no effect whatsoever.

[mrcharly-YHT]

I don't know why such a fuss is made about it.

Bike not falling over is simply due to the rider steering the bike under the direction of fall. Same as balancing a broom on end on your hand. The better the rider gets at noticing and countering a fall, the less they have to move the bike.

Watch a novice, new rider. As they try to keep the bike from falling over, they weave all over the place. After practising for a while they don't weave as much. Now watch someone practise balancing a broom on their hand - same thing.

'trail' is just for altering the steering characteristics. It affects balancing the bike only insomuch as that relies on steering.


The whole gyroscopic thing is a red herring, discounted long long ago.

[Ham]

Wot he sed. If it was gyroscopic effect, when you lock your wheels going down an icy slope, you would fall over instantly instead of waiting until the most painful available spot, as we all know happens.

[clarion]

I still don't understand how, when I'd injured my head, I could balance on a bike better than walking.