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  #21  
Old July 7th 17, 05:46 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 13,447
Default Olmo

On 7/7/2017 10:02 AM, wrote:
On Friday, July 7, 2017 at 7:32:49 AM UTC-7, jbeattie wrote:
On Thursday, July 6, 2017 at 7:44:38 PM UTC-7, wrote:
On Thursday, July 6, 2017 at 10:35:24 AM UTC-7, Joerg wrote:
On 2017-07-05 12:18,
wrote:
On Wednesday, July 5, 2017 at 11:51:51 AM UTC-7, Doug Landau wrote:
Tom are Olmos any good
Any chance this Olmo is a Basso?
https://sacramento.craigslist.org/bik/6185998403.html

Olmo's were as a rule were on a level of Basso or Colnago. I think that they are still made today.

While that particular Olmo is VERY reminiscent of a Basso Gap, it is it's own maker.


What was the big difference in frames back then? I know Italian ones
were usually considered more fancy but my Dutch Gazelle frame looks
nearly identical to this one. Ok, Reynolds steel instead of Columbus.

The wheelbases and rake and trail were quite different and it makes a remarkable difference in feeling and ride. The difference between my Eddy Merckx Corsa Extra and the Basso Lotto is noticeable on the second pedal stroke.


I think that after LeMond and by the '90s, you see more variation in the geometry used by the Italian builders. In the '70s, for example, the differences were minor except for Rigi and some Gios frames. The Bassos, Olmos, Pinarellos, Colnagos, etc. were pretty cookie-cutter, IMO. It was hard to differentiate between some of them with the paint off.


The Colnago didn't have the low bb. It handled more like the Merckx and I believe that Merckx for awhile bought Colnagos and rebadged them.


Merckx brand frames were built by Ernie Clements of Falcon
until he bought his name back and established his own
facility in Belgium under the guidance of Ugo DeRosa.

Merckx did ride Colnagos but aside from a few team bikes
Colnagos are not Merckx.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


Ads
  #22  
Old July 7th 17, 06:50 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default Olmo

On 2017-07-07 08:01, wrote:
On Friday, July 7, 2017 at 7:17:19 AM UTC-7, Joerg wrote:
On 2017-07-07 01:25, John B. wrote:
On Thu, 6 Jul 2017 19:44:35 -0700 (PDT),

wrote:

On Thursday, July 6, 2017 at 10:35:24 AM UTC-7, Joerg wrote:
On 2017-07-05 12:18,
wrote:
On Wednesday, July 5, 2017 at 11:51:51 AM UTC-7, Doug
Landau wrote:
Tom are Olmos any good Any chance this Olmo is a Basso?
https://sacramento.craigslist.org/bik/6185998403.html

Olmo's were as a rule were on a level of Basso or Colnago.
I think that they are still made today.

While that particular Olmo is VERY reminiscent of a Basso
Gap, it is it's own maker.


What was the big difference in frames back then? I know
Italian ones were usually considered more fancy but my Dutch
Gazelle frame looks nearly identical to this one. Ok,
Reynolds steel instead of Columbus.

The wheelbases and rake and trail were quite different and it
makes a remarkable difference in feeling and ride. The
difference between my Eddy Merckx Corsa Extra and the Basso
Lotto is noticeable on the second pedal stroke.


Yes, there could be minor differences in the dimensions which make
a noticeable difference. On the photo they aren't visible. This is
the same frame I ride, same color but larger geometry:

https://www.lfgss.com/conversations/234710/

For some reason those still fetch good money at auction.


I read an article about different handling between different
bikes. The author and his buddy, a frame maker, even cobbled up a
fork with adjustable trail.

Anyway, they found that the Italian frames tended toward lower
bottom bracket heights, in other words lower C/G, which they
attributed to a more stable feeling bike.


I can't imagine the BB to be even lower than on the Dutch frame I
ride. Every time I switch back from the MTB (very high ground
clearance) to the road bike I have to watch during dirt road
stretches not to run into a pedal strike.


If you compare your photo with
https://www.google.com/search?q=Bass...t5ITOtNTl_igM:

you can see a rather large difference in BB height. This difference
is so dramatic that you have to learn to ALWAYS have your inside
pedal up to keep it from dragging on the ground and possibly dumping
you at speed.


I'd say it is about the same. A few days ago I coasted and there was a
rock not larger that the size of a small fist. Lower than the brick in
the photo of the Basso Loto. Didn't pick up the pedal because I was sure
it'll clear it. It didn't. But I didn't crash.

--
Regards, Joerg

http://www.analogconsultants.com/
  #23  
Old July 7th 17, 09:09 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default Stability [ Olmo]

On 2017-07-07 09:24, wrote:
On Friday, July 7, 2017 at 9:10:54 AM UTC-7, Frank Krygowski wrote:
On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different
bikes. The author and his buddy, a frame maker, even cobbled up a
fork with adjustable trail.

Anyway, they found that the Italian frames tended toward lower
bottom bracket heights, in other words lower C/G, which they
attributed to a more stable feeling bike.


As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The
center of mass of a bike+rider is generally somewhere around the
saddle, i.e. maybe 40" high. I'd think lowering the center of mass
by half an inch would make a tiny difference compared to other
changes.

But more important: To me, stability in a bike means it requires
less frequent and energetic steering corrections to maintain
balance. And in that respect, an "ordinary" or "high wheeler" is
far, far more stable than a normal bike. Likewise, a recumbent is
far less stable. The first time I road an ordinary, I was able to
easily balance at 2 mph. The first time I rode a recumbent, I
couldn't even balance. Someone had to run alongside and hold me up
as I flopped left and right, until I could relax and let the bike
work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the
"ordinary's" rider mass at about five feet or more, the sideways
rotation needed for a fall begins much more slowly. There's plenty
of time to correct even the tiniest deviation from vertical. By
contrast, with a recumbent's center of mass at maybe 18", the
sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick
(or meter stick) on its edge, vs. trying to balance a 6" (or 15 cm)
ruler. Or trying to vertically balance a shovel or hammer with
heavy side up vs. down.

So if a higher center of mass is more stable for ordinaries,
yardsticks and other objects, I don't see why it would be opposite
for bikes.


Well you're wrong. Firstly the saddle is also lower since the saddle
height is measured from the pedal center. And in many high speed
corners you put your weight on the outside pedal which is lower. Also
the arc through which it passes is lower. There is about an inch
difference in height and it is very noticeable believe me.


I'll second that. My MTB doesn't corner nearly as well as my much lower
CG road bike and the difference is not in the tires. I've tried with
another MTB that the owner had equipped with slick road tires (he
doesn't own a road bike), same thing.

With MTB cornering often happens in a very different way, keeping the
bike more straight up but leaning out and putting a leg out for
skidding. Like dirt bikers sometimes do.

--
Regards, Joerg

http://www.analogconsultants.com/
  #24  
Old July 7th 17, 09:29 PM posted to rec.bicycles.tech
Doug Landau
external usenet poster
 
Posts: 1,424
Default Olmo

On Wednesday, July 5, 2017 at 11:51:51 AM UTC-7, Doug Landau wrote:
Tom are Olmos any good
Any chance this Olmo is a Basso?
https://sacramento.craigslist.org/bik/6185998403.html


think i need one of these
http://www.ebay.com/itm/302364463733?ul_noapp=true
  #25  
Old July 7th 17, 09:41 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 10,538
Default Stability [ Olmo]

On 7/7/2017 12:24 PM, wrote:
On Friday, July 7, 2017 at 9:10:54 AM UTC-7, Frank Krygowski wrote:
On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different bikes.
The author and his buddy, a frame maker, even cobbled up a fork with
adjustable trail.

Anyway, they found that the Italian frames tended toward lower bottom
bracket heights, in other words lower C/G, which they attributed to a
more stable feeling bike.


As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The center
of mass of a bike+rider is generally somewhere around the saddle, i.e.
maybe 40" high. I'd think lowering the center of mass by half an inch
would make a tiny difference compared to other changes.

But more important: To me, stability in a bike means it requires less
frequent and energetic steering corrections to maintain balance. And in
that respect, an "ordinary" or "high wheeler" is far, far more stable
than a normal bike. Likewise, a recumbent is far less stable. The
first time I road an ordinary, I was able to easily balance at 2 mph.
The first time I rode a recumbent, I couldn't even balance. Someone had
to run alongside and hold me up as I flopped left and right, until I
could relax and let the bike work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the "ordinary's"
rider mass at about five feet or more, the sideways rotation needed for
a fall begins much more slowly. There's plenty of time to correct even
the tiniest deviation from vertical. By contrast, with a recumbent's
center of mass at maybe 18", the sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick (or
meter stick) on its edge, vs. trying to balance a 6" (or 15 cm) ruler.
Or trying to vertically balance a shovel or hammer with heavy side up
vs. down.

So if a higher center of mass is more stable for ordinaries, yardsticks
and other objects, I don't see why it would be opposite for bikes.


Well you're wrong.


OK, explain it with physics.

In a static situation, an object sitting on three or more contact points
is more stable if the center of mass is lower. As I explained above,
it's different for the dynamic situation of an object being balanced on
one or two support points.

Firstly the saddle is also lower since the saddle height is measured from the pedal center.


Sorry, that makes no sense. I was talking about the height of the
center of mass. Besides, a bike with a lower bottom bracket will have
(for the same rider) the same distance between the "pedal center" and
the saddle.


And in many high speed corners you put your weight on the outside pedal which is lower. Also the arc through which it passes is lower. There is about an inch difference in height and it is very noticeable believe me.


So many misconceptions.

"Putting your weight on the lower pedal" does not appreciably change the
height of your center of mass. The mass of your lower leg moves down,
but the mass of the other leg moves up. And no matter what you think
you feel, pushing down on a pedal doesn't put your weight there.

If the height of the center of mass doesn't change, the polar moment of
inertia about the contact patch doesn't change. That polar moment of
inertia is how mass height affects stability. Again, this should be
obvious if you've ridden both an antique "penny farthing" and a
recumbent. Have you?

Seriously, let's talk in terms of physics, not in terms of Jobst's "myth
and lore."

--
- Frank Krygowski
  #26  
Old July 8th 17, 02:00 AM posted to rec.bicycles.tech
John B.[_3_]
external usenet poster
 
Posts: 5,697
Default Stability [ Olmo]

On Fri, 7 Jul 2017 12:10:51 -0400, Frank Krygowski
wrote:

On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different bikes.
The author and his buddy, a frame maker, even cobbled up a fork with
adjustable trail.

Anyway, they found that the Italian frames tended toward lower bottom
bracket heights, in other words lower C/G, which they attributed to a
more stable feeling bike.


As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The center
of mass of a bike+rider is generally somewhere around the saddle, i.e.
maybe 40" high. I'd think lowering the center of mass by half an inch
would make a tiny difference compared to other changes.

But more important: To me, stability in a bike means it requires less
frequent and energetic steering corrections to maintain balance. And in
that respect, an "ordinary" or "high wheeler" is far, far more stable
than a normal bike. Likewise, a recumbent is far less stable. The
first time I road an ordinary, I was able to easily balance at 2 mph.
The first time I rode a recumbent, I couldn't even balance. Someone had
to run alongside and hold me up as I flopped left and right, until I
could relax and let the bike work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the "ordinary's"
rider mass at about five feet or more, the sideways rotation needed for
a fall begins much more slowly. There's plenty of time to correct even
the tiniest deviation from vertical. By contrast, with a recumbent's
center of mass at maybe 18", the sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick (or
meter stick) on its edge, vs. trying to balance a 6" (or 15 cm) ruler.
Or trying to vertically balance a shovel or hammer with heavy side up
vs. down.

So if a higher center of mass is more stable for ordinaries, yardsticks
and other objects, I don't see why it would be opposite for bikes.


I've always sort of wondered about bicycle design. The article I
mentioned is indicative. They made up a special fork that allowed
trail to be changed from several degrees of plus to several degrees of
negative tail. They speculated on what the difference in BB height
would cause. It appears to me that there are no, or people aren't
familiar with, normal basic engineering studies of bicycle design
versus the effects on stability and or handling. Witness your
discussion of balancing a ruler.

If you look into, say aircraft design there are innumerable studies of
dimensional changes versus flight characteristics, or even velocity
versus flight characteristics. Looking at automobile design there are
innumerable studies or, say wheel camber versus degrees of under of
over steer.

Given that the bicycle probably came into common use long before
either the auto or the airplane it seems odd there don't seem to be
standards in design. Or perhaps studies on the effect of various
changes in design versus stability, for example.

Note the usual arguments about "Oooo Aluminum is so stiff". Good Lord!
The effects of modifying the strength and elasticity of materials and
angles making up a triangle have been known since the days of the
early Greeks. Yet the use of a material with well known physical
characteristics in a shape that has been known for 2000 years results
in this jaw gapped evaluating of "Oh, so stiff".

Sigh. But I suppose that the science the is applicable to a device who
is protected by bright flashing beams of light is rather on the order
of "Eye of newt and toe of frog, Wool of bat and tongue of dog".

--
Cheers,

John B.

  #27  
Old July 8th 17, 02:18 AM posted to rec.bicycles.tech
John B.[_3_]
external usenet poster
 
Posts: 5,697
Default Stability [ Olmo]

On Fri, 7 Jul 2017 12:10:51 -0400, Frank Krygowski
wrote:

On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different bikes.
The author and his buddy, a frame maker, even cobbled up a fork with
adjustable trail.

Anyway, they found that the Italian frames tended toward lower bottom
bracket heights, in other words lower C/G, which they attributed to a
more stable feeling bike.


As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The center
of mass of a bike+rider is generally somewhere around the saddle, i.e.
maybe 40" high. I'd think lowering the center of mass by half an inch
would make a tiny difference compared to other changes.

But more important: To me, stability in a bike means it requires less
frequent and energetic steering corrections to maintain balance. And in
that respect, an "ordinary" or "high wheeler" is far, far more stable
than a normal bike. Likewise, a recumbent is far less stable. The
first time I road an ordinary, I was able to easily balance at 2 mph.
The first time I rode a recumbent, I couldn't even balance. Someone had
to run alongside and hold me up as I flopped left and right, until I
could relax and let the bike work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the "ordinary's"
rider mass at about five feet or more, the sideways rotation needed for
a fall begins much more slowly. There's plenty of time to correct even
the tiniest deviation from vertical. By contrast, with a recumbent's
center of mass at maybe 18", the sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick (or
meter stick) on its edge, vs. trying to balance a 6" (or 15 cm) ruler.
Or trying to vertically balance a shovel or hammer with heavy side up
vs. down.

So if a higher center of mass is more stable for ordinaries, yardsticks
and other objects, I don't see why it would be opposite for bikes.


I'm not sure that you are using the correct formula. Generally the
width/length of the object and the effective movement of the C/G
versus the width as the object is tilted is used isn't it? The classic
triangle on it's base versus the triangle on it's apex. In one case
the C.G. is raised as the object is tilted in the other it is lowered.
--
Cheers,

John B.

  #28  
Old July 8th 17, 05:10 AM posted to rec.bicycles.tech
Frank Krygowski[_2_]
external usenet poster
 
Posts: 7,511
Default Stability [ Olmo]

On Friday, July 7, 2017 at 9:00:55 PM UTC-4, John B. wrote:
On Fri, 7 Jul 2017 12:10:51 -0400, Frank Krygowski wrote:

On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different bikes.
The author and his buddy, a frame maker, even cobbled up a fork with
adjustable trail.

Anyway, they found that the Italian frames tended toward lower bottom
bracket heights, in other words lower C/G, which they attributed to a
more stable feeling bike.


As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The center
of mass of a bike+rider is generally somewhere around the saddle, i.e.
maybe 40" high. I'd think lowering the center of mass by half an inch
would make a tiny difference compared to other changes.

But more important: To me, stability in a bike means it requires less
frequent and energetic steering corrections to maintain balance. And in
that respect, an "ordinary" or "high wheeler" is far, far more stable
than a normal bike. Likewise, a recumbent is far less stable. The
first time I road an ordinary, I was able to easily balance at 2 mph.
The first time I rode a recumbent, I couldn't even balance. Someone had
to run alongside and hold me up as I flopped left and right, until I
could relax and let the bike work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the "ordinary's"
rider mass at about five feet or more, the sideways rotation needed for
a fall begins much more slowly. There's plenty of time to correct even
the tiniest deviation from vertical. By contrast, with a recumbent's
center of mass at maybe 18", the sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick (or
meter stick) on its edge, vs. trying to balance a 6" (or 15 cm) ruler.
Or trying to vertically balance a shovel or hammer with heavy side up
vs. down.

So if a higher center of mass is more stable for ordinaries, yardsticks
and other objects, I don't see why it would be opposite for bikes.


I've always sort of wondered about bicycle design. The article I
mentioned is indicative. They made up a special fork that allowed
trail to be changed from several degrees of plus to several degrees of
negative tail. They speculated on what the difference in BB height
would cause. It appears to me that there are no, or people aren't
familiar with, normal basic engineering studies of bicycle design
versus the effects on stability and or handling. Witness your
discussion of balancing a ruler.

If you look into, say aircraft design there are innumerable studies of
dimensional changes versus flight characteristics, or even velocity
versus flight characteristics. Looking at automobile design there are
innumerable studies or, say wheel camber versus degrees of under of
over steer.

Given that the bicycle probably came into common use long before
either the auto or the airplane it seems odd there don't seem to be
standards in design. Or perhaps studies on the effect of various
changes in design versus stability, for example.

Note the usual arguments about "Oooo Aluminum is so stiff". Good Lord!
The effects of modifying the strength and elasticity of materials and
angles making up a triangle have been known since the days of the
early Greeks. Yet the use of a material with well known physical
characteristics in a shape that has been known for 2000 years results
in this jaw gapped evaluating of "Oh, so stiff".

Sigh. But I suppose that the science the is applicable to a device who
is protected by bright flashing beams of light is rather on the order
of "Eye of newt and toe of frog, Wool of bat and tongue of dog".

--
Cheers,

John B.


There have been many attempts to mathematically understand bicycle stability.
It turns out that it's a marvelously complicated topic. The mathematics
researchers generate is beyond what I'm willing to try to understand; and I've
done a lot of mathematics.

Look up the work of Jim Papdopoulos, for example.
http://www.nature.com/news/the-bicyc...matics-1.20281

Fortunately, in this discussion I'm not attempting to deal with the general
problem. I'm examining only one tiny aspect: the influence of the height of
the center of mass. I'd say that's pretty easy to understand.

- Frank Krygowski
  #29  
Old July 8th 17, 05:17 AM posted to rec.bicycles.tech
Frank Krygowski[_2_]
external usenet poster
 
Posts: 7,511
Default Stability [ Olmo]

On Friday, July 7, 2017 at 9:19:23 PM UTC-4, John B. wrote:
On Fri, 7 Jul 2017 12:10:51 -0400, Frank Krygowski wrote:

On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different bikes.
The author and his buddy, a frame maker, even cobbled up a fork with
adjustable trail.

Anyway, they found that the Italian frames tended toward lower bottom
bracket heights, in other words lower C/G, which they attributed to a
more stable feeling bike.


As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The center
of mass of a bike+rider is generally somewhere around the saddle, i.e.
maybe 40" high. I'd think lowering the center of mass by half an inch
would make a tiny difference compared to other changes.

But more important: To me, stability in a bike means it requires less
frequent and energetic steering corrections to maintain balance. And in
that respect, an "ordinary" or "high wheeler" is far, far more stable
than a normal bike. Likewise, a recumbent is far less stable. The
first time I road an ordinary, I was able to easily balance at 2 mph.
The first time I rode a recumbent, I couldn't even balance. Someone had
to run alongside and hold me up as I flopped left and right, until I
could relax and let the bike work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the "ordinary's"
rider mass at about five feet or more, the sideways rotation needed for
a fall begins much more slowly. There's plenty of time to correct even
the tiniest deviation from vertical. By contrast, with a recumbent's
center of mass at maybe 18", the sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick (or
meter stick) on its edge, vs. trying to balance a 6" (or 15 cm) ruler.
Or trying to vertically balance a shovel or hammer with heavy side up
vs. down.

So if a higher center of mass is more stable for ordinaries, yardsticks
and other objects, I don't see why it would be opposite for bikes.


I'm not sure that you are using the correct formula. Generally the
width/length of the object and the effective movement of the C/G
versus the width as the object is tilted is used isn't it? The classic
triangle on it's base versus the triangle on it's apex. In one case
the C.G. is raised as the object is tilted in the other it is lowered.


The base width is a factor in the case of a stable object with three or more
contact points with the ground. It doesn't apply in the case we're discussing,
where the axis relevant to stability is the ine connectin two tire contact
points. When viewed from the front or back, the bike is effectively balancing
on an edge. When lateral tipping begins, the bike+rider center of mass does not
rise.

- Frank Krygowski
  #30  
Old July 8th 17, 09:16 AM posted to rec.bicycles.tech
John B.[_3_]
external usenet poster
 
Posts: 5,697
Default Stability [ Olmo]

On Fri, 7 Jul 2017 21:10:57 -0700 (PDT), Frank Krygowski
wrote:

On Friday, July 7, 2017 at 9:00:55 PM UTC-4, John B. wrote:
On Fri, 7 Jul 2017 12:10:51 -0400, Frank Krygowski wrote:

On 7/7/2017 4:25 AM, John B. wrote:

I read an article about different handling between different bikes.
The author and his buddy, a frame maker, even cobbled up a fork with
adjustable trail.

Anyway, they found that the Italian frames tended toward lower bottom
bracket heights, in other words lower C/G, which they attributed to a
more stable feeling bike.

As I've said many times, I'm far from being a connoisseur of bike
handling. But it doesn't make sense to me that a lower center of
gravity would make a bike feel more stable.

First, the effect would seem to be minuscule if it existed. The center
of mass of a bike+rider is generally somewhere around the saddle, i.e.
maybe 40" high. I'd think lowering the center of mass by half an inch
would make a tiny difference compared to other changes.

But more important: To me, stability in a bike means it requires less
frequent and energetic steering corrections to maintain balance. And in
that respect, an "ordinary" or "high wheeler" is far, far more stable
than a normal bike. Likewise, a recumbent is far less stable. The
first time I road an ordinary, I was able to easily balance at 2 mph.
The first time I rode a recumbent, I couldn't even balance. Someone had
to run alongside and hold me up as I flopped left and right, until I
could relax and let the bike work properly.

The difference is polar moment of inertia about the axis along the
ground between the two tire contact patches. With the "ordinary's"
rider mass at about five feet or more, the sideways rotation needed for
a fall begins much more slowly. There's plenty of time to correct even
the tiniest deviation from vertical. By contrast, with a recumbent's
center of mass at maybe 18", the sideways rotation initiates quickly.

The same effect can be observed by trying to balance a yardstick (or
meter stick) on its edge, vs. trying to balance a 6" (or 15 cm) ruler.
Or trying to vertically balance a shovel or hammer with heavy side up
vs. down.

So if a higher center of mass is more stable for ordinaries, yardsticks
and other objects, I don't see why it would be opposite for bikes.


I've always sort of wondered about bicycle design. The article I
mentioned is indicative. They made up a special fork that allowed
trail to be changed from several degrees of plus to several degrees of
negative tail. They speculated on what the difference in BB height
would cause. It appears to me that there are no, or people aren't
familiar with, normal basic engineering studies of bicycle design
versus the effects on stability and or handling. Witness your
discussion of balancing a ruler.

If you look into, say aircraft design there are innumerable studies of
dimensional changes versus flight characteristics, or even velocity
versus flight characteristics. Looking at automobile design there are
innumerable studies or, say wheel camber versus degrees of under of
over steer.

Given that the bicycle probably came into common use long before
either the auto or the airplane it seems odd there don't seem to be
standards in design. Or perhaps studies on the effect of various
changes in design versus stability, for example.

Note the usual arguments about "Oooo Aluminum is so stiff". Good Lord!
The effects of modifying the strength and elasticity of materials and
angles making up a triangle have been known since the days of the
early Greeks. Yet the use of a material with well known physical
characteristics in a shape that has been known for 2000 years results
in this jaw gapped evaluating of "Oh, so stiff".

Sigh. But I suppose that the science the is applicable to a device who
is protected by bright flashing beams of light is rather on the order
of "Eye of newt and toe of frog, Wool of bat and tongue of dog".

--
Cheers,

John B.


There have been many attempts to mathematically understand bicycle stability.
It turns out that it's a marvelously complicated topic. The mathematics
researchers generate is beyond what I'm willing to try to understand; and I've
done a lot of mathematics.

Look up the work of Jim Papdopoulos, for example.
http://www.nature.com/news/the-bicyc...matics-1.20281

Fortunately, in this discussion I'm not attempting to deal with the general
problem. I'm examining only one tiny aspect: the influence of the height of
the center of mass. I'd say that's pretty easy to understand.

- Frank Krygowski


What you seem to be saying is that a bicycle 100 feet tall would be
far more stable then one 1 foot tall and I'm not sure that is correct.
If this logic is applied then it would be easier to stand on a one
inch broomstick 10 feet tall rather then a 1 inch broomstick 1 inch
tall.

Re the papdopoulos problem I think (without any great effort being
expended) is that the problem is trying to analyze an object with a
number of forces acting on it simultaneously by considering each
separate force, when, I suggest, the results are the results of a
combination of forces.

The dihedral of an aircraft wing, for example, tends to keep the wings
level..... as long as the wing is moving forward through the air.
--
Cheers,

John B.

 




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