How does a bicycle stay upright?

General cycling advice ( NOT technical ! )
nirakaro
Posts: 1575
Joined: 22 Dec 2007, 2:01am

How does a bicycle stay upright?

Post by nirakaro »

Start of an article (I haven'tread any further yet) in this week's New Scientist -

"In 2011, an international team of bi-pedal enthusiasts dropped the bombshell that, despite 150 years of analysis, no one knows how a bicycle stays upright. Across the world, riders dismounted and stared at their bikes in disbelief. What they had been doing for years was a feat inexplicable by science.

Well, sort of. “What we don’t know are the simple, necessary or sufficient conditions for a bicycle to be self-stable,” says Andy Ruina, an engineer at Cornell University in Ithaca, New York.

We have relied on trial-and-error engineering to construct stable bikes that aren’t prone to toppling while in motion. Explaining how they work mathematically requires around 25 variables, such as the angle of the front forks relative to the road, weight distribution and wheel size.

Before 2011, researchers had reduced this profusion to two things. One was the size of "
Brucey
Posts: 44454
Joined: 4 Jan 2012, 6:25pm

Re: How does a bicycle stay upright?

Post by Brucey »

it must be magic then? :wink: :roll:

More recently some clever maths (solving complex differential equations) has been claimed to have solved this and the results can be plotted as a stability index. Maybe someone will yet prove this wrong in some way but so far it is holding up, in terms of basic stability (sack of potatoes in the saddle). [What it doesn't do is tell you how the nut behind the wheel changes things, or how the whole thing behaves in a crosswind etc...]

But seriously, a lack of fundamental understanding has hampered efforts to design different steering systems for two-wheeled vehicles. Even professional engineers at MIT have spent thousands of hours building stuff and trying it out because it couldn't be predicted how it might really behave otherwise.

I am actually just about to build 'a new thing' and I've been thinking about it for over 30 years. My idea has been evolving in that time but it is some comfort to me that my first idea I thought might be worth building (which I still thought wouldn't be good enough, so didn't) has since been independently thought of and built as someone else's fifth idea, having wasted man-years of effort in the meantime on other stuff that was always going to be hopeless. Even so it was the best thing they came up with.... so watch this space!

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
mick skinner
Posts: 552
Joined: 15 Aug 2007, 7:57pm
Location: ilkeston, derbyshire

Re: How does a bicycle stay upright?

Post by mick skinner »

User avatar
pjclinch
Posts: 5457
Joined: 29 Oct 2007, 2:32pm
Location: Dundee, Scotland
Contact:

Re: How does a bicycle stay upright?

Post by pjclinch »

[youtube]oZAc5t2lkvo[/youtube]
Often seen riding a bike around Dundee...
Mattyfez
Posts: 354
Joined: 22 Dec 2014, 7:24pm

Re: How does a bicycle stay upright?

Post by Mattyfez »

[youtube]NeXIV-wMVUk[/youtube]
User avatar
Audax67
Posts: 5999
Joined: 25 Aug 2011, 9:02am
Location: Alsace, France
Contact:

Re: How does a bicycle stay upright?

Post by Audax67 »

It's all done by angels, I tell you. ANGELS ! ! !
Have we got time for another cuppa?
User avatar
Mick F
Spambuster
Posts: 56349
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: How does a bicycle stay upright?

Post by Mick F »

Walter Lewin wrote:None of this is intuitive.

Yes it is.

As for why a bike stays upright, I ain't got a clue but it's nowt to do with gyroscopic stabilisation.
Mick F. Cornwall
User avatar
Mick F
Spambuster
Posts: 56349
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: How does a bicycle stay upright?

Post by Mick F »

As kids, we would delight on riding on the playing fields and jumping off the back and watching our bikes carry on without us.

Two of us had jobs with the local paper shop who gave us big black bikes with the large front basket carriers. Me and my mate would set off towards each other, jump off the back and watch our paper-shops bike collide head-on. :lol: :lol:

Happy care-free days.
Mick F. Cornwall
User avatar
al_yrpal
Posts: 11526
Joined: 25 Jul 2007, 9:47pm
Location: Think Cheddar and Cider
Contact:

Re: How does a bicycle stay upright?

Post by al_yrpal »

The bigger diameter the wheel the heavier the wheel and the faster its moving forward the more stable the bike is. Therefore I believe the gyroscopic effect is a big factor. Other than that its just personal balance or lack of it - remember your first attempt at riding a bike? I watched my son on his first day on a two wheeler, he must have fallen off 40 times, but by the end of the day he could ride because the bruises taught him how to balance. A combination of personal balance and gyroscopic stability resisting a tendency to tilt, or precess just like a gyroscope does, thats what does it. (and why Bromptons with their tiny wheels are less stable)

Al
Reuse, recycle, thus do your bit to save the planet.... Get stuff at auctions, Dump, Charity Shops, Facebook Marketplace, Ebay, Car Boots. Choose an Old House, and a Banger ..... And cycle as often as you can......
axel_knutt
Posts: 2869
Joined: 11 Jan 2007, 12:20pm

Re: How does a bicycle stay upright?

Post by axel_knutt »

Ruina is professor of mechanical engineering at Cornell, he was on the World Service (at 12m15s) four years ago.

He's here, too.
“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
― Friedrich Nietzsche
User avatar
NATURAL ANKLING
Posts: 13780
Joined: 24 Oct 2012, 10:43pm
Location: English Riviera

Re: How does a bicycle stay upright?

Post by NATURAL ANKLING »

Hi,
Mick F wrote:
Walter Lewin wrote:None of this is intuitive.

Yes it is.
As for why a bike stays upright, I ain't got a clue but it's nowt to do with gyroscopic stabilisation.

Wrong.
https://en.wikipedia.org/wiki/Precession
"Precession or gyroscopic considerations have an effect on bicycle performance at high speed."
2015-09-08_160201.jpg
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
TonyR
Posts: 5390
Joined: 31 Aug 2008, 12:51pm

Re: How does a bicycle stay upright?

Post by TonyR »

NATURAL ANKLING wrote:Hi,
Mick F wrote:
Walter Lewin wrote:None of this is intuitive.

Yes it is.
As for why a bike stays upright, I ain't got a clue but it's nowt to do with gyroscopic stabilisation.

Wrong.
https://en.wikipedia.org/wiki/Precession
"Precession or gyroscopic considerations have an effect on bicycle performance at high speed."


Wikipedia isn't always right. Bikes have been built and tested that had counter-rotating wheels to null out any gyroscopic effect. The stability of the bike was unchanged. See e.g. http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm
Brucey
Posts: 44454
Joined: 4 Jan 2012, 6:25pm

Re: How does a bicycle stay upright?

Post by Brucey »

there are several elements to the system that alter its dynamic characteristics including gyroscopic effects, trail effects, headstock rise and fall, the weight distribution, the compliance and any natural resonance characteristics of the structure (which includes the rider).

They all make a difference to a real bicycle but no single factor is solely responsible for stability under all conditions. Researchers have built test machines which eliminate or in some cases even reverses the usual geometry and under certain conditions you can still get 'stability' of a kind, even with no gyro force, no trail (or even trail in the reverse direction). It mightn't make for a nice riding bicycle though. IME some bikes are just very difficult to ride no hands; sometimes this is because of something prosaic like bad alignment or a sticky headset, but other times it is 'something else' i.e. the bicycle recipe is not quite right, not for that kind of riding.

So I've never ridden a Brompton or a Moulton no hands (maybe I didn't try hard enough?) and I'm not right keen on bar bags and most types of front pannier either, for similar reasons.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
mark a.
Posts: 1375
Joined: 8 Jan 2007, 2:47pm
Location: Surrey

Re: How does a bicycle stay upright?

Post by mark a. »

Anyone who says that it's "definitely" or "definitely not" to do with X is almost certainly wrong.
User avatar
NATURAL ANKLING
Posts: 13780
Joined: 24 Oct 2012, 10:43pm
Location: English Riviera

Re: How does a bicycle stay upright?

Post by NATURAL ANKLING »

Hi,
You need to look carefully at the videos.
You need gravity for any gyroscopic aid so the bike does not fall over, other wise the the bike would stay upright with out motion.
A bicycle has castor and trail for stability and steering axis is angled so it has self centring steering.
Locking the steering means that the gyroscopic effect will not work correctly by removing the ability for the front wheel to swivel.

A bike with no gyroscopic effect but has rotating wheels and steering :?:
Wheel touching ground in front of steering axis..................but spot the clever front extended boom and bob weight :?:

Double front wheel that nulls gyroscopic effect irrespective of rotation of the extra wheel :?:
But the bike has a rider....................
Just as I ride my bike slowly its harder but possible not impossible..............

Two rotating wheels sharing the same fixed axis would just change the precession by cancelling out or adding to it but you still have the rear wheel and the rider..............................

I would like to see a bike with two matched counter-rotating wheels and no rider........................

My second skip trainer is a real pig to ride no hands.......................but I forgot the banana front wheel I straightened and the obvious twisted frame..........I need to hit 25 MPH before I get no hand stability......below 20 MPH it goes pear shaped......

Brucey sums up well......................and you always have the rider...............
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
Post Reply