A Cycling & bikes forum. CycleBanter.com

Go Back   Home » CycleBanter.com forum » rec.bicycles » Techniques
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

"The Stability of the Bicycle"



 
 
Thread Tools Display Modes
  #31  
Old October 7th 03, 03:56 PM
PotatoSmack
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Its all a mater of momentum. The linear momentum of the bike and rider
is far greater than that of the wheel, at any speed. here is an
experiment. try pushing someone who is pushing a bike.
notice how hard it is.
You turn the bike by changing your momentum by leaning. The front
wheel is only following your path.
John Docherty
Ads
  #32  
Old October 7th 03, 03:57 PM
jim beam
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

wow. you've just completely rewritten the world of physics. absolutely
extroardinary.

look, take a bike wheel, suspend one end of the axle from a piece of
string, then spin it in the normal vertical position. the wheel will
appear to "defy gravity" by remaining near vertical with its axis
perpendicular to the string. then you will notice that the wheel axis
is itself rotating around the string. this is because the reolved
resoulution of simple newtonian physics resolves at 90 degrees to the
applied force, i.e. the string pulls up against the wheel's center of
gravity axis, so the wheel moves at 90, thus rotating.

when you tilt a fork of a bike with a rotating wheel in it, there's no
reason for the physical world to suddenly distort and suddenly run
counter to normal.

as has been described by a previous poster, a vehicle ith no rotating
components still banks & steers satisfactorily. gyro forces DO NOT make
the bike bank. if you don't want to believe me [sic], just dig out that
old high school physics footage of a bike being ridden with a counter
gyroscopic wheelset. works just fine.

jb.

  #33  
Old October 7th 03, 04:01 PM
jim beam
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Their presence is
demonstrable without delving into jargon and mathematical proofs.


hmmmm. now you're in the same territory as your new metal fatigue
hypothesis.

come on jobst, you're the engineer. this is a tech forum. get with the
science. drop the conjecture. please.

jb.

  #34  
Old October 7th 03, 04:42 PM
Benjamin Lewis
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

jim beam wrote:

wow. you've just completely rewritten the world of physics. absolutely
extroardinary.

look, take a bike wheel, suspend one end of the axle from a piece of
string, then spin it in the normal vertical position. the wheel will
appear to "defy gravity" by remaining near vertical with its axis
perpendicular to the string. then you will notice that the wheel axis is
itself rotating around the string. this is because the reolved
resoulution of simple newtonian physics resolves at 90 degrees to the
applied force,
i.e. the string pulls up against the wheel's center of gravity axis, so the
wheel moves at 90, thus rotating.

when you tilt a fork of a bike with a rotating wheel in it, there's no
reason for the physical world to suddenly distort and suddenly run
counter to normal.

as has been described by a previous poster, a vehicle ith no rotating
components still banks & steers satisfactorily. gyro forces DO NOT make
the bike bank.


Umm. I really think you need to re-read what he wrote.

if you don't want to believe me [sic], just dig out that
old high school physics footage of a bike being ridden with a counter
gyroscopic wheelset. works just fine.


And is reportedly "almost impossible" to ride no-hands, as Jobst has
claimed.

--
Benjamin Lewis

Seeing is deceiving. It's eating that's believing.
-- James Thurber
  #35  
Old October 7th 03, 05:08 PM
jim beam
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

as Jobst has
claimed.


that's proof?

  #36  
Old October 7th 03, 05:28 PM
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Simon Brooke writes:

Take the wheel out, spin it in you hands and try to tilt it to
the left or right and note the force of the steering action.
This should convince you of its effect.


please explain. gyro reaction is _90 degrees to the applied
force_. i.e. my front wheel, spinning "forwards" tries to tilt top
rightwards when turned to the left. you seem to be implying that
gyro recation is responsible for banking the bike to the left when
steered left.


No, when you wheel the bike along holding onto the seat you steer
by banking the bike and the turn is a reaction to the bank.
Banking the bike to the left will tend to initiate a turn to the
left. But the gyroscopic force is quite small when the wheel is
spun at only walking speed and the geometry of the bike also
results in the wheel turning left in response to a left bank (even
when the wheel isn't rotating).


Well, just so. I agree that you can get strong gyroscopic effects
with a fast rotating wheel, but I'm completely unpersuaded that they
are significant at walking speed. So, again, has anyone done the
maths?


There are no "maths", math is an aggregate concept and has no plural...
except in GB maybe.

I guess you don't have a bicycle with a QR front wheel so you can't
perform the simple experiment of turning the wheel at "walking speed"
to fell the strong gyroscopic effect caused by tilting the wheel
manually to the left and right.

Jobst Brandt

  #37  
Old October 7th 03, 05:38 PM
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Simon Brooke writes:

That the bicycle does not steer when stationary shows that effect
as well. To make the bicycle steer merely from rake and trail
takes a large lean angle and does not accomplish the same effect.


OK, I have just been out to the bike shed and carried out an
empirical experiment; and this is just false. My observations are,
when stationary:


(i) On rougher surface (grass), greater lean angles are required
before a steering effect is noticed as compared to smoother surfaces
(tiled floor).


(ii) On tyres with a larger contact patch (mountain bike), greater
lean angles are required before a steering effect is noticed as
compared to smaller contact patch (road bike).


(iii) All bikes on all surfaces showed steering effect on lean.


(iv) Road bike on tiled floor showed to within the limits of
observational measurement as much steering effect on the same amount
of lean when stationary as when moving.


(v) By contrast, a mountain bike on grass had to be leant to a
considerable angle to show any steering effect when stationary, and
when the steering effect did occur it occured in jerky movements
through considerable angles.


From this I conclude that the resistance to steering when stationary
is as much due to friction at the contact patch as anything else
(and, lets face it, tyres are designed to generate the maximum
possible friction at the contact patch).


I'm quite prepared to repeat the experiment on camera an post a
quicktime movie. But it's a very simple experiment and I'm sure
everyone else can repeat it too.


No need to belabor what is self evident. We have all parked a bicycle
either leaning against a wall or on a kick-stand and seen that the
front wheel turns to the side to which the bicycle leans. This is not
what steers the bicycle in this exercise.

When walking a bicycle, holding it by the saddle, lean angles are
trivially small and cause steering by gyroscopic action, the test for
which you have apparently not done. Take the wheel out of the
bicycle, turn it at "walking speed" and tilt it to the left and right
in your hands. You will notice a quick and relatively forceful
steering response. It is this force that allows the bicycle to be
steered by slight lean angles, the method of riding no-hands and the
forces that cause shimmy. If you cannot ride no-hands you'll have to
leave it at wheeling the bicycle by the saddle.

Jobst Brandt

  #38  
Old October 7th 03, 05:41 PM
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Simon Brooke writes:

What is the relative contribution of the different effects - ie to
what degree is the above more important than the effects of rake
and trail - at different speeds and with the addition of the rider
to the whole system.


As a child I rode one winter a bicycle which had a normal rear wheel
but had part of an old ski bolted onto the front forks in place of
the front wheel. It was good fun to use and I don't remember it
handling noticably differently from a normal bike. This is a long
time ago and I could be wrong, but again it's easy enough to verify.


Oh! Tell me how far you rode it riding no-hands and how you wheeled
it while walking and holding it by the saddle.

This isn't to deny that gyroscopic effects play some part, nor that
the influence of gyroscopic effects increases with speed; but
without some maths I'm skeptical about their being significant as
compared to lean.


Well don't just sit there and fret about it, try it. Take the wheel
out and turn it.

Jobst Brandt

  #39  
Old October 7th 03, 05:53 PM
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Jim Beam writes:

wow. you've just completely rewritten the world of physics.
absolutely extroardinary.


You'll have to be more explicit. What is it that you find
extraordinary and contrary to "the world of physics"?

Look, take a bike wheel, suspend one end of the axle from a piece of
string, then spin it in the normal vertical position. The wheel will
appear to "defy gravity" by remaining near vertical with its axis
perpendicular to the string. Then you will notice that the wheel axis
is itself rotating around the string. This is because the reolved
resoulution of simple newtonian physics resolves at 90 degrees to the
applied force, i.e. the string pulls up against the wheel's center of
gravity axis, so the wheel moves at 90, thus rotating.


In spite of the garbled text, I don't see in what way this contradicts
steering a bicycle using these forces, if I deciphered it correctly.
By the way, have you performed this experiment or did you only read
about it? If you have done this, you'll note that the axle of the
wheel remains in a horizontal plane down rotation speed of the wheel
below one revolution per second.

When you tilt a fork of a bike with a rotating wheel in it, there's
no reason for the physical world to suddenly distort and suddenly
run counter to normal.


What do you mean by this. Can you translate that to plain English?

As has been described by a previous poster, a vehicle ith no rotating
components still banks & steers satisfactorily. Gyro forces DO NOT make
the bike bank.


I think you have that backwards, banking (or leaning) the bicycle to
one side or the other causes the wheel to turn, not the converse.

If you don't want to believe me [sic], just dig out that old high
school physics footage of a bike being ridden with a counter
gyroscopic wheelset. Works just fine.


I'm not familiar with your "footage".

Jobst Brandt

  #40  
Old October 7th 03, 06:06 PM
David Damerell
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

"jim beam" wrote:
Benjamin Lewis:
"jim beam"
as Jobst has claimed.

that's proof?


There's a neat piece of selective quoting. What this should read is;

old high school physics footage of a bike being ridden with a counter
gyroscopic wheelset. works just fine.

And is reportedly "almost impossible" to ride no-hands, as Jobst has
claimed.


I.e., the behaviour of this bike substantiates Jobst's claim.
--
David Damerell Kill the tomato!
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
A song for Carla John Harlow Mountain Biking 3 May 10th 04 02:29 PM
Those bicycle builders big mistake! Garrison Hilliard General 30 December 23rd 03 07:03 AM
Reports from Sweden Garry Jones General 17 October 14th 03 05:23 PM
Reports from Sweden Garry Jones Social Issues 14 October 14th 03 05:23 PM


All times are GMT +1. The time now is 11:21 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 CycleBanter.com.
The comments are property of their posters.