Block chain and wooden spokes

Carl Fogel said:

Nice view of block chain and sprocket on an 1893 Elliott hickory
bicycle:

http://www.nostalgic.net/pictures/1649.htm

Quoted message said:

The compact frame metal bike used not only wooden rims, but wooden
spokes:

http://www.nostalgic.net/pictures/1645.htm
http://www.nostalgic.net/pictures/1650.htm
http://www.nostalgic.net/pictures/1646.htm

You forgot to say that the hubs in these wheels hang from the top
spokes.

Jobst Brandt

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Carl Fogel said:

Nice view of block chain and sprocket on an 1893 Elliott hickory
bicycle:

http://www.nostalgic.net/pictures/1649.htm

Quoted message said:

The compact frame metal bike used not only wooden rims, but wooden
spokes:

http://www.nostalgic.net/pictures/1645.htm
http://www.nostalgic.net/pictures/1650.htm
http://www.nostalgic.net/pictures/1646.htm

You forgot to say that the hubs in these wheels hang from the top
spokes.

Jobst Brandt

I thought all spoke wheels hung from the top spokes, with the load getting
less as you radiate from the top, with some smaller percentage of the load
being on the bottom spokes.

DI said:

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Carl Fogel said:

Nice view of block chain and sprocket on an 1893 Elliott hickory
bicycle:

http://www.nostalgic.net/pictures/1649.htm

Quoted message said:

The compact frame metal bike used not only wooden rims, but wooden
spokes:

http://www.nostalgic.net/pictures/1645.htm
http://www.nostalgic.net/pictures/1650.htm
http://www.nostalgic.net/pictures/1646.htm

You forgot to say that the hubs in these wheels hang from the top
spokes.

Jobst Brandt

I thought all spoke wheels hung from the top spokes, with the load getting
less as you radiate from the top, with some smaller percentage of the load
being on the bottom spokes.

Dear DI,

Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke bicycle
wheels and faintly pre-compressed wooden-spoke wagon wheels behave the
same way--just about all the measurable action occurs in the spokes
under the hub, which show compression (the same thing as loss of
pre-tension).

Both theory and measurement show that 5~6 spokes in a 36-spoke
pre-tensioned wire-spoke wheel _lose_ considerable tension as they
roll under the hub (the rim flattens toward the hub at the contact
patch).

All the other spokes show a slight gain in tension.

Here's a pdf with graphs of actual strain gauge measurements of a
single spoke as the bicycle is ridden:

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf

See figures 10 & 11, The huge icicle-spikes are where the
pre-tensioned spoke rolled under the hub and lost tension.

Here's a page with the theory side:

http://www.astounding.org.uk/ian/wheel/index.html

In the large table, look at the rightmost two columns, where T
(tension) and C (compression) for the 36 spokes are split by sign. The
tricky part is remembering that a spoke pointing somewhat downward
from the hub (say 8 o'clock) is actually pulling the hub _down_ as its
tension increases.

It's a very annoying concept, since the naive expectation is that the
bicycle spokes pointing up from the hub should show a huge increase in
tension as the hub "hangs" the rider's weight from the rim. But it
doesn't. The rim flattens toward the hub from the contact patch,
shortening the distance between rim and hub and consequently losing
spoke tension in that area. The other spokes stubbornly refuse to
change tension anywhere near as much.

RBT posters love to squabble about this.

Cheers,

Carl Fogel

Carl Fogel said:

Here's a pdf with graphs of actual strain gauge measurements of a
single spoke as the bicycle is ridden:

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf

Quoted message said:

See figures 10 & 11, The huge icicle-spikes are where the
pre-tensioned spoke rolled under the hub and lost tension.

I find interesting that Gavin still avoids even slight mention of what
moved him to perform this work. He cites Pippard, who really did have
it all wrong. As I experienced it, Gavin was originally spurred on by
publication of "the Bicycle Wheel" with which he strongly disagreed at
the time. The paper in the above pdf takes a more parallel view but
has enough Greek letters and log, log/log, and linear graphs to
impress the man on the street. In contrast, the web site below shows
roughly the same figures as shown in "the Bicycle Wheel".

I wonder if these authors also get the "you have it all wrong! The
wheel cannot stand on its spokes." that appears here from the UK about
once per year.

Quoted message said:

Here's a page with the theory side:

Quoted message said:

http://www.astounding.org.uk/ian/wheel/index.html

Quoted message said:

In the large table, look at the rightmost two columns, where T
(tension) and C (compression) for the 36 spokes are split by
sign. The tricky part is remembering that a spoke pointing somewhat
downward from the hub (say 8 o'clock) is actually pulling the hub
_down_ as its tension increases.

Quoted message said:

It's a very annoying concept, since the naive expectation is that
the bicycle spokes pointing up from the hub should show a huge
increase in tension as the hub "hangs" the rider's weight from the
rim. But it doesn't. The rim flattens toward the hub from the
contact patch, shortening the distance between rim and hub and
consequently losing spoke tension in that area. The other spokes
stubbornly refuse to change tension anywhere near as much.

Quoted message said:

RBT posters love to squabble about this.

Especially from the UK

Jobst Brandt

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:

[...]

Quoted message said:

Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke bicycle
wheels and faintly pre-compressed wooden-spoke wagon wheels behave the
same way--just about all the measurable action occurs in the spokes
under the hub, which show compression (the same thing as loss of
pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

None of this has anything to do with whether the wheel "hangs from the
top spokes" or "stands on the bottom spokes" in either kind of wheel.
Hanging and standing are both consistent, depending on your use of
language, with the correct physical interpretations of either
pre-tensioned or pre-compressed wheels.

Quoted message said:

Carl Fogel writes:

[...]

Quoted message said:

Quoted message said:

It's a very annoying concept, since the naive expectation is that
the bicycle spokes pointing up from the hub should show a huge
increase in tension as the hub "hangs" the rider's weight from the
rim. But it doesn't. The rim flattens toward the hub from the
contact patch, shortening the distance between rim and hub and
consequently losing spoke tension in that area. The other spokes
stubbornly refuse to change tension anywhere near as much.

Quoted message said:

RBT posters love to squabble about this.

Especially from the UK

http://mathworld.wolfram.com/Rabbit-DuckIllusion.html

Is this a duck or a rabbit?

Ben C said:

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:
[...] Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke
bicycle wheels and faintly pre-compressed wooden-spoke wagon wheels
behave the same way--just about all the measurable action occurs in
the spokes under the hub, which show compression (the same thing as
loss of pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

None of this has anything to do with whether the wheel "hangs from the
top spokes" or "stands on the bottom spokes" in either kind of wheel.
Hanging and standing are both consistent, depending on your use of
language, with the correct physical interpretations of either
pre-tensioned or pre-compressed wheels.

It's all very simple really, in any sensible and self consistent use of
English

A
: Something is standing if the forces which support it push up from below
: Something is hanging if the forces which support it pull up from above

B
:The spokes below a cycle wheel hub, pull down
:The spokes above a cycle wheel hub pull up.

C
:The forces supporting the hub pull up from above

http://home.comcast.net/~jlulm/Free_Body_Diagram_of_hub.pdf

pk

Ben C said:

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:

[...]

Quoted message said:

Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke bicycle
wheels and faintly pre-compressed wooden-spoke wagon wheels behave the
same way--just about all the measurable action occurs in the spokes
under the hub, which show compression (the same thing as loss of
pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

None of this has anything to do with whether the wheel "hangs from the
top spokes" or "stands on the bottom spokes" in either kind of wheel.
Hanging and standing are both consistent, depending on your use of
language, with the correct physical interpretations of either
pre-tensioned or pre-compressed wheels.

Dear Ben,

I don't know if your theory about heavily pre-compressed wheels is
correct, but I'd love to see a practical example.

Off-hand, I wonder if you're mistaken. Under load, the round wheel rim
will flatten at the contact patch toward the hub, shortening the
distance between the rim and the hub and compressing the lowermost
spokes even more.

That is, a load acting downward should push even harder on the
pre-compressed spoke under it, compressing it even more. Your theory
seems to require the axle to rise under a load.

But I could be the one who's mistaken.

In any case, a real wooden wagon wheel is only faintly compressed by
the shrinking of an iron band, just enough to keep things together,
not the huge compression that you seem to have in mind.

As the wooden parts dry and compress and shift, the wooden wheel
loosens inside the unchanged iron rim band. There's no wooden
equivalent of a well-built bicycle wheel that lasts until the brakes
wear the rim out.

In fact, really light, elegant wooden carriage wheels should be taken
off. If you leave the weight of the carriage on them, the wood creeps
and deforms and you end up with out-of-round wheels:

"In fact, the rim of the wheel bent, rather like a bow, under the
weight of the chariot, and, just as a bow must not be left strung for
any length of time, so the weight must not be left on the wheels of a
chariot. In the evening, therefore, one either tipped the vehicle
vertically against a wall with the weight off the wheels, as
Telemachus did in Book IV of the Odyssey, or else one took the wheels
off altogether. Even on Mount Olympus the goddess Hebe had the morning
chore of fitting the wheels to the chariot of grey-eyed Athene. With
the much heavier wheels of later times such a procedure is less
necessary and less practicable, although I understand that the wheels
of the present [1978] Lord Mayor's coach are distinctly eccentric,
presumably because the weight has been left on them for long periods.*

*This sort of thing is at the root of most of the stories about
V.I.P.'s becoming seasick when riding in state-coaches."

--"Structures," J.E. Gordon, p. 146

Unlike light wooden wheels, heavy wagon wheels just loosen after
enough use. When a wagon wheel loosens enough to rattle alarmingly,
you take it off, soak it in the creek overnight, and hope that it will
swell up enough to get you into town, where the blacksmith can fit a
new and slightly shorter rim strap.

Cheers,

Carl Fogel

In article <[email hidden]>,

Ben C said:

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:

[...]

Quoted message said:

Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke bicycle
wheels and faintly pre-compressed wooden-spoke wagon wheels behave the
same way--just about all the measurable action occurs in the spokes
under the hub, which show compression (the same thing as loss of
pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

None of this has anything to do with whether the wheel "hangs from the
top spokes" or "stands on the bottom spokes" in either kind of wheel.
Hanging and standing are both consistent, depending on your use of
language, with the correct physical interpretations of either
pre-tensioned or pre-compressed wheels.

No, it is not the case that "Hanging and standing are both
consistent, depending on your use of language,". When the wheel is
loaded the spokes between the contact patch shorten a lot, and the
spokes opposite the contact patch spokes change almost not at all.
When a structure is loaded the load path is determined by the
changes in dimensions, not by a debate in the English department
or among the purveyors of critical studies.

--
Michael Press

p.k. said:

Ben C said:

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:
[...] Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke
bicycle wheels and faintly pre-compressed wooden-spoke wagon wheels
behave the same way--just about all the measurable action occurs in
the spokes under the hub, which show compression (the same thing as
loss of pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

None of this has anything to do with whether the wheel "hangs from the
top spokes" or "stands on the bottom spokes" in either kind of wheel.
Hanging and standing are both consistent, depending on your use of
language, with the correct physical interpretations of either
pre-tensioned or pre-compressed wheels.

It's all very simple really, in any sensible and self consistent use of
English

A
: Something is standing if the forces which support it push up from below
: Something is hanging if the forces which support it pull up from above

B
:The spokes below a cycle wheel hub, pull down
:The spokes above a cycle wheel hub pull up.

C
:The forces supporting the hub pull up from above

I think this is perfectly clear and makes good sense. But on the other
hand, Michael Press also makes a good point. This is why I think it's a
duck-rabbit. It may be that in more technical circles the idea that load
path is represented by strain change (i.e. weight stands on bottom
spokes) ahem carries more weight.

Ben C said:

I think this is perfectly clear and makes good sense. But on the other
hand, Michael Press also makes a good point. This is why I think it's
a duck-rabbit. It may be that in more technical circles the idea that
load path is represented by strain change (i.e. weight stands on
bottom spokes) ahem carries more weight.

Good artcle on load path here:

http://www.brantacan.co.uk/loadpath.htm

have a look at the diagram 5 on page 1.

A vertical mast supported by tensioned stays.

Consider a steady wind from the left to right.

The stays on the right increase in tension, the stays on the left decrease
in tension.

Which stays are stopping the mast falling?

pk

Michael Press wrote:
..

Quoted message said:

When a structure is loaded the load path is determined by the
changes in dimensions,

No!

in a static system, the load path is determined by where the forces act and
their direction. the previous history of the system is not relevant to the
current static situation

"The load path is the route by which forces applied by the ground can exert
the forces necessary to balance the loads."
http://www.brantacan.co.uk/loadpath.htm

pk

Ben C said:

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:

[...]

Quoted message said:

Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke bicycle
wheels and faintly pre-compressed wooden-spoke wagon wheels behave the
same way--just about all the measurable action occurs in the spokes
under the hub, which show compression (the same thing as loss of
pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

I'm afraid you're wrong about this.

p.k. said:

Ben C said:

Quoted message said:

On Tue, 15 May 2007 17:16:16 -0500, "DI" <[email hidden]> wrote:
[...] Sorry, but Jobst is just joking. Both pre-tensioned wire-spoke
bicycle wheels and faintly pre-compressed wooden-spoke wagon wheels
behave the same way--just about all the measurable action occurs in
the spokes under the hub, which show compression (the same thing as
loss of pre-tension).

If the spokes were pre-compressed with a pre-compression greater than
the load you're putting on the wheel, you would see no change in the
bottom spokes and a reduction in compression in the top spokes.

None of this has anything to do with whether the wheel "hangs from the
top spokes" or "stands on the bottom spokes" in either kind of wheel.
Hanging and standing are both consistent, depending on your use of
language, with the correct physical interpretations of either
pre-tensioned or pre-compressed wheels.

It's all very simple really, in any sensible and self consistent use of
English

A
: Something is standing if the forces which support it push up from below
: Something is hanging if the forces which support it pull up from above

B
:The spokes below a cycle wheel hub, pull down
:The spokes above a cycle wheel hub pull up.

C
:The forces supporting the hub pull up from above

http://home.comcast.net/~jlulm/Free_Body_Diagram_of_hub.pdf

pk

This is wrong.

The bottom spokes actually contribute to the net downward force on the
hub; i.e., they pull down on the hub, not push up, regardless of their
value, ***change in value***, or force history.

The "change in value" part is where it goes wrong.

p.k. said:

Ben C said:

I think this is perfectly clear and makes good sense. But on the other
hand, Michael Press also makes a good point. This is why I think it's
a duck-rabbit. It may be that in more technical circles the idea that
load path is represented by strain change (i.e. weight stands on
bottom spokes) ahem carries more weight.

Good artcle on load path here:

http://www.brantacan.co.uk/loadpath.htm

A rather bad article, actually.

Quoted message said:

have a look at the diagram 5 on page 1.

A vertical mast supported by tensioned stays.

Consider a steady wind from the left to right.

The stays on the right increase in tension, the stays on the left decrease
in tension.

Not on my mast.

Peter Cole said:

p.k. said:

Ben C said:

I think this is perfectly clear and makes good sense. But on the
other hand, Michael Press also makes a good point. This is why I
think it's a duck-rabbit. It may be that in more technical circles
the idea that load path is represented by strain change (i.e.
weight stands on bottom spokes) ahem carries more weight.

Good artcle on load path here:

http://www.brantacan.co.uk/loadpath.htm

A rather bad article, actually.

Quoted message said:

have a look at the diagram 5 on page 1.

A vertical mast supported by tensioned stays.

Consider a steady wind from the left to right.

The stays on the right increase in tension, the stays on the left
decrease in tension.

Not on my mast.

oops , i stasted the opposite wind direction!

pk

p.k. said:

Michael Press wrote:
.

Quoted message said:

When a structure is loaded the load path is determined by the
changes in dimensions,

No!

in a static system, the load path is determined by where the forces act and
their direction. the previous history of the system is not relevant to the
current static situation

"The load path is the route by which forces applied by the ground can exert
the forces necessary to balance the loads."

Yes, and in a bicycle wheel, the load path is from the contact patch
through the rim and the few spokes near the contact patch to the axle.

Peter Cole said:

p.k. said:

Michael Press wrote:
.

Quoted message said:

When a structure is loaded the load path is determined by the
changes in dimensions,

No!

in a static system, the load path is determined by where the forces
act and their direction. the previous history of the system is not
relevant to the current static situation

"The load path is the route by which forces applied by the ground
can exert the forces necessary to balance the loads."

Yes, and in a bicycle wheel, the load path is from the contact patch
through the rim and the few spokes near the contact patch to the axle.

What is the direction of the force exerted on the hub by the few spoke near
the contact patch?

Up: supporting

or

Down pulling down?

pk

Quoted message said:

Carl Fogel said:

Here's a pdf with graphs of actual strain gauge measurements of a
single spoke as the bicycle is ridden:

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf

Quoted message said:

See figures 10 & 11, The huge icicle-spikes are where the
pre-tensioned spoke rolled under the hub and lost tension.

I find interesting that Gavin still avoids even slight mention of what
moved him to perform this work. He cites Pippard, who really did have
it all wrong. As I experienced it, Gavin was originally spurred on by
publication of "the Bicycle Wheel" with which he strongly disagreed at
the time. The paper in the above pdf takes a more parallel view but
has enough Greek letters and log, log/log, and linear graphs to
impress the man on the street. In contrast, the web site below shows
roughly the same figures as shown in "the Bicycle Wheel".

I wonder if these authors also get the "you have it all wrong! The
wheel cannot stand on its spokes." that appears here from the UK about
once per year.

Quoted message said:

Here's a page with the theory side:

Quoted message said:

http://www.astounding.org.uk/ian/wheel/index.html

Quoted message said:

In the large table, look at the rightmost two columns, where T
(tension) and C (compression) for the 36 spokes are split by
sign. The tricky part is remembering that a spoke pointing somewhat
downward from the hub (say 8 o'clock) is actually pulling the hub
_down_ as its tension increases.

Quoted message said:

It's a very annoying concept, since the naive expectation is that
the bicycle spokes pointing up from the hub should show a huge
increase in tension as the hub "hangs" the rider's weight from the
rim. But it doesn't. The rim flattens toward the hub from the
contact patch, shortening the distance between rim and hub and
consequently losing spoke tension in that area. The other spokes
stubbornly refuse to change tension anywhere near as much.

Quoted message said:

RBT posters love to squabble about this.

Especially from the UK

here's another example of geographically based ignorance: palo alto
"engineers" seem to know nothing about fatigue, fracture mechanics,
principles of deformation, anisotropy, ndt, bearings, etc. or even that
wheels "standing" on their spokes is simply a function of localized rim
deformation....