Re: Snaping Spokes

Doug Huffman said:

Quoted message said:

There is NO WAY that a mechanical engineer would use spokes as
compression members. Sorry, not going to buy it!!!

Quoted message said:

I would guess that tensioned wheels evolved, likely from compression
wheels, rather than springing forth fully developed.

I've thought about that and don't believe the origin was that direct.
There are many hoops strung with threads and some even have insets in
their center such as crab traps with a bait ring in the center.
Rolling one of these around could give a bright young man ideas for
other applications.

In any case, I think the first tensile wheels would be interesting to
find and how they were used. Unfortunately this is lost in history,
probably because other advances of greater interest overshadowed the
tensioned wheel at the time, and besides, it was only a different
wheel of which there were many.

Jobst Brandt
[email hidden]

Doug Huffman said:

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

Quoted message said:

There is NO WAY that a mechanical
engineer would use spokes as compression members.
Sorry, not going to buy it!!!

I would guess that tensioned wheels evolved, likely from compression wheels,
rather than springing forth fully developed.

Dear Doug,

While I like evolutionary explanations in biology, I confess
that I have trouble seeing how a compression wheel could
change gradually into a tension wheel.

That is, I can't figure out an intermediate step between
stiff wooden spokes compressed by a shrunk-on iron band and
wire spokes in tension.

But I'd love to see some comments or even guesses about the
appearance of the tensioned wheel.

Thanks for raising an interesting question.

Carl Fogel

Quoted message said:

Doug Huffman said:

Quoted message said:

There is NO WAY that a mechanical engineer would use spokes as
compression members. Sorry, not going to buy it!!!

Quoted message said:

I would guess that tensioned wheels evolved, likely from compression
wheels, rather than springing forth fully developed.

I've thought about that and don't believe the origin was that direct.
There are many hoops strung with threads and some even have insets in
their center such as crab traps with a bait ring in the center.
Rolling one of these around could give a bright young man ideas for
other applications.

In any case, I think the first tensile wheels would be interesting to
find and how they were used. Unfortunately this is lost in history,
probably because other advances of greater interest overshadowed the
tensioned wheel at the time, and besides, it was only a different
wheel of which there were many.

Jobst Brandt
[email hidden]

Dear Jobst,

It really is an interesting question.

Although string can work for a tensile wheel, I expect that
it pretty much has to be kevlar and is still a novelty.

I'd guess that the tensile wheel only became possible when
steel wire reached reasonable quality and when decent metal
threading became cheap.

The bicycle wheel is odd because it has to be both strong
and light.

Cart wheels have to be strong, but I think that lightness
was achieved mostly by better material and flimsier
wheels--compression wheels heading toward what we call
stupid-lite.

Spinning wheels didn't have to be strong, so thinner spokes
and rims made them light enough. If hand spinning hadn't
been killed off by industrialization, I expect that the
wooden spinning wheel in my grandmother's house would have
been made by the same companies that manufactured the big
wheels on penny-farthings. But hand spinning just died out,
so there was no move to change the technology.

Railroad wheels, your other interest, never headed toward
tensile--I imagine that weight wasn't a big consideration
compared to strength.

Were there wire-spoke wheels before Starley? I have a vague
notion that the earliest wire-spoke bicycles were all
British.

Carl Fogel

On Sat, 05 Mar 2005 19:25:59 -0700, [email hidden] may have

Quoted message said:

Were there wire-spoke wheels before Starley? I have a vague
notion that the earliest wire-spoke bicycles were all
British.

Iron wheels with iron-rod spokes appear on certain implement designs
from the early 19th century, but it's unlikely that tension was
included in their design. On the other hand, those all-iron wheels
may have been one source of inspiration for the wire-spoked wheel. As
jobst says, though, the records are lost in history.

--
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<[email hidden]> wrote: (clip) I can't figure out an intermediate
step between stiff wooden spokes compressed by a shrunk-on iron band andwire
spokes in tension.(clip)
^^^^^^^^^^^^^^^^^
Carl, these are the steps I can visualize, although I cannot cite historical
examples, and I don't really know whether they ever existed:
1.) Wooden wheel, with wooden compression spokes.
2.) Cast iron wheel with solid web, or heavy compression spokes.
3.) Cast iron wheel with light compression spokes, and limited durability.
4,) Steel wheel with steel spokes--stronger and lighter than cast iron
wheel. Insight that the upper spokes are carrying tension.
5.) Steel wheel with thin spokes, in which both compression and tension are
developed.
6.) Wheel with wire spokes.

Leo Lichtman said:

<[email hidden]> wrote: (clip) I can't figure out an intermediate
step between stiff wooden spokes compressed by a shrunk-on iron band andwire
spokes in tension.(clip)
^^^^^^^^^^^^^^^^^
Carl, these are the steps I can visualize, although I cannot cite historical
examples, and I don't really know whether they ever existed:
1.) Wooden wheel, with wooden compression spokes.
2.) Cast iron wheel with solid web, or heavy compression spokes.
3.) Cast iron wheel with light compression spokes, and limited durability.
4,) Steel wheel with steel spokes--stronger and lighter than cast iron
wheel. Insight that the upper spokes are carrying tension.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^?

Quoted message said:

5.) Steel wheel with thin spokes, in which both compression and tension are
developed.
6.) Wheel with wire spokes.

Dear Leo,

It's the step between 4 and 5 that's puzzling.

The upper spokes in a compression wheel shouldn't show
tension, should they?

That is, on a wagon-wheel-style wheel with hefty iron spokes
in compression rather than tension, you could probably cut
all the spokes out of a motionless wheel except the one
directly under the hub.

I think that you should be able to cut off everything just
above 3 and 9 o'clock on such a wheel when motionless.

Maybe there's a little tension or compression in the upper
spoke of a wooden/iron compression wheel?

Here's where Jobst is probably raising his eyebrows and
wondering how people like me can be in any doubt about how
old-fashioned stagecoach wheels worked. With luck, someone
who's thought about compression wheels (and solid wheels,
which are a little different) will tell us how their spokes
work.

Carl Fogel

Carl Fogel said:

Quoted message said:

Quoted message said:

> There is NO WAY that a mechanical engineer would use spokes as
> compression members. Sorry, not going to buy it!!!

Quoted message said:

Quoted message said:

Quoted message said:

I would guess that tensioned wheels evolved, likely from
compression wheels, rather than springing forth fully developed.

Quoted message said:

Quoted message said:

I've thought about that and don't believe the origin was that
direct. There are many hoops strung with threads and some even
have insets in their center such as crab traps with a bait ring in
the center. Rolling one of these around could give a bright young
man ideas for other applications.

Quoted message said:

Quoted message said:

In any case, I think the first tensile wheels would be interesting
to find and how they were used. Unfortunately this is lost in
history, probably because other advances of greater interest
overshadowed the tensioned wheel at the time, and besides, it was
only a different wheel of which there were many.

Quoted message said:

It really is an interesting question.

Quoted message said:

Although string can work for a tensile wheel, I expect that it
pretty much has to be Kevlar and is still a novelty.

This can be done with less than Kevlar strength for threads, you just
need more of them. I think the process developed in a few jumps.

Quoted message said:

I'd guess that the tensile wheel only became possible when steel
wire reached reasonable quality and when decent metal threading
became cheap.

The steel wire was one of the first and obvious building elements but
the cable was not, as we see with the introduction of it by the John
Roebling. The first big applications were suspension bridges and the
one that stands out is the Brooklyn bridge.

http://www.endex.com/gf/buildings/bbridge/bbridgefacts.htm

Before that a great visionary built the first suspension bridge across
the Danube in Budapest as we know it today as the Chain Bridge.

http://www.aviewoncities.com/budapest/chainbridge.htm
http://www.virtourist.com/europe/budapest/20.htm
http://www.pbase.com/al309/image/8107989
http://personal.udri.udayton.edu/klosterm/Budapest/n2074.jpg

Quoted message said:

The bicycle wheel is odd because it has to be both strong
and light.

That's no different from the suspension bridge that has only spokes
(suspenders), the main cables (rim), and deck (tire), taken loosely.

Quoted message said:

Cart wheels have to be strong, but I think that lightness was
achieved mostly by better material and flimsier wheels--compression
wheels heading toward what we call stupid-lite.

Interestingly elegant wooden spoked wheels like those developed for a
shay already required dish for stability as these wheels got slimmer
and lighter, and I believe the term applies there much better than
bicycle rear wheels and probably was coined in the days of wagon
wheels. They were also prestressed but in compression by the steel
tire.

From the wheelwright's dictionary:

# Dish: The inward, or concave angle at which the spoke is set into
# the hub giving the wheel a cone-shaped appearance. The dishing
# provides greater strength and security to the wheel.

Quoted message said:

Spinning wheels didn't have to be strong, so thinner spokes and rims
made them light enough. If hand spinning hadn't been killed off by
industrialization, I expect that the wooden spinning wheel in my
grandmother's house would have been made by the same companies that
manufactured the big wheels on penny-farthings. But hand spinning
just died out, so there was no move to change the technology.

They were ideal because their weight was right for the job. A
tensioned wheel required a stronger rim and probably couldn't be made
as light as the wooden ones that were strong enough for the job.

Quoted message said:

Railroad wheels, your other interest, never headed toward tensile--I
imagine that weight wasn't a big consideration compared to strength.

That's a whole different ball of wax. Those wheels are shrunk onto an
axle and that interface had cause plenty of problems as did the thin
webs between the hub and rim. Once trains started going faster and
light weight entered the mix, the pair of wheels on an axle became
resonators and rail-wheel noise today is a major study for high speed
trains. The Swiss probably had the loudest passenger cars of all with
their 1960's commute cars, some of which are still in service and make
an awful rushing noise.

Quoted message said:

Were there wire-spoke wheels before Starley? I have a vague notion
that the earliest wire-spoke bicycles were all British.

Starley came up with cross-lacing to solve the broken spoke problem
with high wheelers... that went away shortly after he came up with the
idea but still too late to spare us from his tied spoke crossings.
Besides, they didn't have mush tension either because the rims were
too weak and the huge spoke complement, even with light tension
overwhelmed those steel rims.

Jobst Brandt
[email hidden]

Carl Fogel said:

The upper spokes in a compression wheel shouldn't show tension,
should they?

Quoted message said:

That is, on a wagon-wheel-style wheel with hefty iron spokes in
compression rather than tension, you could probably cut all the
spokes out of a motionless wheel except the one directly under the
hub.

Quoted message said:

I think that you should be able to cut off everything just above 3
and 9 o'clock on such a wheel when motionless.

Quoted message said:

Maybe there's a little tension or compression in the upper spoke of
a wooden/iron compression wheel?

Quoted message said:

Here's where Jobst is probably raising his eyebrows and wondering
how people like me can be in any doubt about how old-fashioned
stagecoach wheels worked. With luck, someone who's thought about
compression wheels (and solid wheels, which are a little different)
will tell us how their spokes work.

Carl, I think you need to review the section of "the Bicycle Wheel" on
how wheels support loads. The radial load distribution diagram is
identical for all spoked wheels.

Jobst Brandt
[email hidden]

<[email hidden]> wrote: It's the step between 4 and 5 that's
puzzling. The upper spokes in a compression wheel shouldn't show tension,
should they? (clip)
^^^^^^^^^^^^^
Dear Carl,

Let's compare two wheels with compression spokes. The first is a used,
dried out old wooden wagon wheel. The second is a farm implement wheel with
a steel rim, a steel hub, and round welded steel spokes. On the first, as
the wheel rolls, the spokes at the bottom carry all of the load. The spokes
above the hub develop clearance at their joint with the rim, so they clearly
cannot develop tension.

On the steel wheel, the spokes are welded into the rim. As load is applied
to the hub, the hub gets closer to the ground, putting the bottom spokes in
compression. The movement of the hub cannot occur without stretching the
upper spokes, which, of course, means that they are in tension, and must be
helping support the load.

The principal change beyond that, in developing the wire wheel, is the
superposition of high, even tension on all the spokes, which permits the
lower spokes to go into "compression" structurally, while remaining in
tension internally.

I believe this last part is what the OP failed to grasp.

On Sun, 06 Mar 2005 17:25:21 GMT, "Leo Lichtman"

may have said:

The principal change beyond that, in developing the wire wheel, is the
superposition of high, even tension on all the spokes, which permits the
lower spokes to go into "compression" structurally, while remaining in
tension internally.

I believe this last part is what the OP failed to grasp.

Indeed, this is the leap of counterintuition which seems to cause the
greatest amount of confusion; it really does work that way from the
standpoint of the entire wheel as a functional structure, even though
as a single finite element it is difficult to conceive of a spoke
working in that manner.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

On Sat, 05 Mar 2005 22:28:40 -0700, [email hidden] may have

Quoted message said:

Leo Lichtman said:

4,) Steel wheel with steel spokes--stronger and lighter than cast iron
wheel. Insight that the upper spokes are carrying tension.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^?

Quoted message said:

5.) Steel wheel with thin spokes, in which both compression and tension are
developed.
6.) Wheel with wire spokes.

Dear Leo,

It's the step between 4 and 5 that's puzzling.

The upper spokes in a compression wheel shouldn't show
tension, should they?

I looked closely at a couple of very old implement wheels a while
back, and was a bit surprised to see that in the case of these
particular ones, the spokes were not welded to the rim, but rather
passed through it and upset on the outer side. I have no idea how old
they were, nor where they came from or what the brand of item was that
they were on; they were in a collection of disused farm equipment that
was being sold for its value as antiques and decorations. It's quite
possible that there was no actual tension on the spokes at rest, and
they may have been made with a shoulder that butted against the inside
of the rim; I didn't think to look for that. Still, the germ of the
idea may have been present.

Quoted message said:

I think that you should be able to cut off everything just
above 3 and 9 o'clock on such a wheel when motionless.

In a perfect world, perhaps, but a spoked wooden wagon wheel without
compression from its band will collapse *sideways* in short order.
That's according to a wheelwright who makes them for some of the
wagons that are used in the annual Trail Rides that are tradtional in
the week leading to the opening of the Houston Livestock Show and
Rodeo.

Quoted message said:

Maybe there's a little tension or compression in the upper
spoke of a wooden/iron compression wheel?

More than a little, from what he was saying.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Leo Lichtman said:

<[email hidden]> wrote: It's the step between 4 and 5 that's
puzzling. The upper spokes in a compression wheel shouldn't show tension,
should they? (clip)
^^^^^^^^^^^^^
Dear Carl,

Let's compare two wheels with compression spokes. The first is a used,
dried out old wooden wagon wheel. The second is a farm implement wheel with
a steel rim, a steel hub, and round welded steel spokes. On the first, as
the wheel rolls, the spokes at the bottom carry all of the load. The spokes
above the hub develop clearance at their joint with the rim, so they clearly
cannot develop tension.

On the steel wheel, the spokes are welded into the rim. As load is applied
to the hub, the hub gets closer to the ground, putting the bottom spokes in
compression. The movement of the hub cannot occur without stretching the

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

upper spokes, which, of course, means that they are in tension, and must be

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

helping support the load.

The principal change beyond that, in developing the wire wheel, is the
superposition of high, even tension on all the spokes, which permits the
lower spokes to go into "compression" structurally, while remaining in
tension internally.

I believe this last part is what the OP failed to grasp.

Dear Leo,

I'm not following you, but maybe we're not talking about the
same kind of non-pre-tensioned wheel.

If spokes are welded neutrally to a hub and rim--no
significant tension or compression--then a load placed on
the hub will compress the lower spoke by deflecting the rim
upward where it meets the ground.

Why would the upper spokes experience tension and stretch
downward?

Carl Fogel

Werehatrack said:

On Sat, 05 Mar 2005 22:28:40 -0700, [email hidden] may have

Quoted message said:

Leo Lichtman said:

4,) Steel wheel with steel spokes--stronger and lighter than cast iron
wheel. Insight that the upper spokes are carrying tension.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^?

Quoted message said:

5.) Steel wheel with thin spokes, in which both compression and tension are
developed.
6.) Wheel with wire spokes.

Dear Leo,

It's the step between 4 and 5 that's puzzling.

The upper spokes in a compression wheel shouldn't show
tension, should they?

I looked closely at a couple of very old implement wheels a while
back, and was a bit surprised to see that in the case of these
particular ones, the spokes were not welded to the rim, but rather
passed through it and upset on the outer side. I have no idea how old
they were, nor where they came from or what the brand of item was that
they were on; they were in a collection of disused farm equipment that
was being sold for its value as antiques and decorations. It's quite
possible that there was no actual tension on the spokes at rest, and
they may have been made with a shoulder that butted against the inside
of the rim; I didn't think to look for that. Still, the germ of the
idea may have been present.

Quoted message said:

I think that you should be able to cut off everything just
above 3 and 9 o'clock on such a wheel when motionless.

In a perfect world, perhaps, but a spoked wooden wagon wheel without
compression from its band will collapse *sideways* in short order.
That's according to a wheelwright who makes them for some of the
wagons that are used in the annual Trail Rides that are tradtional in
the week leading to the opening of the Houston Livestock Show and
Rodeo.

Quoted message said:

Maybe there's a little tension or compression in the upper
spoke of a wooden/iron compression wheel?

More than a little, from what he was saying.

Dear Werehatrack,

Yes, load-bearing wooden wheels like wagon wheels are
compressed and dished by the shrunk-on metal rim strip. The
dishing is needed for the side-loads of 4-wheel wagons (they
have a nasty habit of failing sideways).

The compression of the metal rim strip is needed just to
hold the wheel together--without it, the sections fly apart
at any speed. There's some mortise work, but the tapered
spokes are just jammed into holes bored into the separate
curved sections of wood that make up the rim. It's
tinker-toy construction that needs a rubber band just to
hold it together.

But the spoke load is carried entirely by further
compression by the lower wooden spoke--if anything, the
upper wooden spoke might experience a little decompression,
but I don't think that this would amount to anything like
"hanging from the upper spoke" in the sense of a pre-tension
wheel "standing" on its lower spoke.

Carl Fogel

On Sun, 06 Mar 2005 12:44:33 -0700, [email hidden] may have

Quoted message said:

If spokes are welded neutrally to a hub and rim--no
significant tension or compression--then a load placed on
the hub will compress the lower spoke by deflecting the rim
upward where it meets the ground.

Why would the upper spokes experience tension and stretch
downward?

If the lower spokes compress (or. more likely, deflect), the rim will
presumably not flatten in that area; the result would be that the rim
would be pushed out of concentricity with the hub, producing tension
on the spokes on the opposite side.

Given the compressibility of iron spokes, I have my doubts about how
significant this force would be without a heavy load, but the absence
of a thing in fact has never been a bar to firm belief in its
existence for many people. And, for that matter, I'd allow that it's
possible that with a high enough load, the transfer could be present.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Quoted message said:

Carl Fogel said:

The upper spokes in a compression wheel shouldn't show tension,
should they?

Quoted message said:

That is, on a wagon-wheel-style wheel with hefty iron spokes in
compression rather than tension, you could probably cut all the
spokes out of a motionless wheel except the one directly under the
hub.

Quoted message said:

I think that you should be able to cut off everything just above 3
and 9 o'clock on such a wheel when motionless.

Quoted message said:

Maybe there's a little tension or compression in the upper spoke of
a wooden/iron compression wheel?

Quoted message said:

Here's where Jobst is probably raising his eyebrows and wondering
how people like me can be in any doubt about how old-fashioned
stagecoach wheels worked. With luck, someone who's thought about
compression wheels (and solid wheels, which are a little different)
will tell us how their spokes work.

Carl, I think you need to review the section of "the Bicycle Wheel" on
how wheels support loads. The radial load distribution diagram is
identical for all spoked wheels.

Jobst Brandt
[email hidden]

Dear Jobst,

For solid spokes, yes.

But is a loose wooden-spoke wheel with a compressing iron
rim band a different matter?

The wooden spokes are loose at both ends, but jammed between
the separate wooden rim sections and the hub by the
compression of the shrunk-on iron band.

The lower spoke carries the load in compression.

What does the upper wooden spoke do?

On a pre-tensioned wheel there's a slight increase in
tension in the upper spoke (and most of the other spokes) as
the lower spokes lose tension.

On the loose wooden-spoke compression-band wheel, I think
that the band lengthens slightly as the wheel is loaded
because the band flattens out a little against the ground,
taking a shortcut, a chord across its previously circular
path.

So the band loses tension, the lower spoke takes a
compressive load, and the upper spoke--I think--loses a
little tension, instead of gaining, the opposite of the
upper spoke on the pre-tension bicycle wheel.

It may even be that all the other spokes (except for the
lowermost ones) lose a little tension, too, as the iron band
relaxes slightly when the load is placed on the hub and
flattens out the bottom of the wheel and rim strip.

But this is just speculation, since I don't have any idea
how much compression the shrunk-on iron band really
provides, or how much of the wooden-spoke wheel's integrity
depends on the rough-and-ready press fit of the tapered
spokes being jammed into tapered holes, green wood versus
dry, and so forth.

And my notion of how it all fits together may miss a step
that changes everything.

Carl Fogel

Werehatrack said:

On Sun, 06 Mar 2005 12:44:33 -0700, [email hidden] may have

Quoted message said:

If spokes are welded neutrally to a hub and rim--no
significant tension or compression--then a load placed on
the hub will compress the lower spoke by deflecting the rim
upward where it meets the ground.

Why would the upper spokes experience tension and stretch
downward?

If the lower spokes compress (or. more likely, deflect), the rim will
presumably not flatten in that area; the result would be that the rim
would be pushed out of concentricity with the hub, producing tension
on the spokes on the opposite side.

Given the compressibility of iron spokes, I have my doubts about how
significant this force would be without a heavy load, but the absence
of a thing in fact has never been a bar to firm belief in its
existence for many people. And, for that matter, I'd allow that it's
possible that with a high enough load, the transfer could be present.

Dear Werehatrack,

Why wouldn't the lower rim just flatten when a load is
placed on the hub, the way it does with other wheels?

Carl Fogel

<[email hidden]> wrote: (clip)a load placed on the hub will compress
the lower spoke by deflecting the rim upward where it meets the ground. Why
would the upper spokes experience tension and stretch downward?
^^^^^^^^^^^^^^
Carl, I think we are on the threshhold of a breakthrough here. If the wheel
is flexible, like a tire, I can see that it could flatten, as you say. And
since it is elastic, to some extent I am sure this happens. On the other
hand, imagine that the wheel is of very heavy construction, and the spokes
are light. The wheel would tend to remain round, putting the lower spokes
in compression, as we have agreed. If the lower spokes are in compression,
they have become shorter. If the wheel is still round, the upper spokes
necessarily have to get longer. In order to get longer they develop tensile
stress. And, of course, this means they are pulling up on the hub, helping
to support the load.

Just for the sake of completeness, let's compare what happens to two wheels
with loose spokes. In the shaky, wooden-spoked wagon wheel, we have already
agreed that the load must be carried entirely by the bottom spokes. If you
rode a bicycle with really loose spokes, the load hangs entirely from the
upper spokes. Any case in between must see the load shift to some degree
from bottom to top, or top to bottom, so the load is carried by top and
bottom.

On Sun, 06 Mar 2005 13:15:25 -0700, [email hidden] may have

Quoted message said:

Werehatrack said:

If the lower spokes compress (or. more likely, deflect), the rim will
presumably not flatten in that area; the result would be that the rim
would be pushed out of concentricity with the hub, producing tension
on the spokes on the opposite side.

Dear Werehatrack,

Why wouldn't the lower rim just flatten when a load is
placed on the hub, the way it does with other wheels?

Iron may be both malleable and elastic, but it's also quite stiff. If
it was flimsy enough to flatten *that* much, it would probably not be
heavy enough to last long.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

dianne_1234 said:

Leo Lichtman said:

<[email hidden]> wrote: (clip)a load placed on the hub will compress
the lower spoke by deflecting the rim upward where it meets the ground. Why
would the upper spokes experience tension and stretch downward?
^^^^^^^^^^^^^^
Carl, I think we are on the threshhold of a breakthrough here. If the wheel
is flexible, like a tire, I can see that it could flatten, as you say. And
since it is elastic, to some extent I am sure this happens. On the other
hand, imagine that the wheel is of very heavy construction, and the spokes
are light. The wheel would tend to remain round, putting the lower spokes
in compression, as we have agreed. If the lower spokes are in compression,
they have become shorter. If the wheel is still round, the upper spokes
necessarily have to get longer. In order to get longer they develop tensile
stress. And, of course, this means they are pulling up on the hub, helping
to support the load.

Just for the sake of completeness, let's compare what happens to two wheels
with loose spokes. In the shaky, wooden-spoked wagon wheel, we have already
agreed that the load must be carried entirely by the bottom spokes. If you
rode a bicycle with really loose spokes, the load hangs entirely from the
upper spokes. Any case in between must see the load shift to some degree
from bottom to top, or top to bottom, so the load is carried by top and
bottom.

I think Leo's on to something. One key to my understanding is the
relative stiffness of rim vs. spokes.

Most of the people I've talked to picture the rim as rigid and the
spokes as flexible, as if the wheel were spoked with rubber bands.

In real life, most bicycle rims are several times more flexible than
even a single spoke. I can easily flex a bare rim several millimeters
with my bare hands. But I can't stretch a single spoke as all, as far
as I can tell by looking.

Dear Dianne,

I'm not sure if you're talking about the pre-tensioned
bicycle wheel here.

With no spokes and no tension, rims flex easily.

But in real life, the amount of flex in a rim compressed by
the tremendous spoke tension is as invisible to the naked
eye as the stretch in the lowermost spoke--both the spoke
and the rim move the same amount.

I may have to sneak over to my neighbor's yard and peek more
closely at the decorative rusting, dried-out wagon wheels
chained with padlocks to posts as landscaping material.

A classic wagon-wheel spoke provides no strength in tension
beyond friction--the tapered stick of wood that is the spoke
would simply pull away from the hub on one end and the wheel
section on the other end.

This kind of spoke is just a broomstick, slightly tapered on
each end (think "spoke-shave"😉 and shoved into bored holes
in a hub at one end and a wheel section at the other.

It's a tinker-toy design writ large. To keep the spoke (or
wheel section) from flying off, a red-hot iron band is
slipped over the assembled wooden jigsaw puzzle and shrinks
into place, compressing all the pieces. When the band
breaks, the wheel falls apart, usually within a single
revolution.

Carl Fogel