The Basics of Wheel Alignment and Wheelbuilding

Weisse Luft wrote in message ...
No, I am not confused. If you know how to draw a free body diagram,
you will see the error in your ways if you can accurately measure the
rim deflection.

Pretensioned structures easily confuse those who study them. Rest
assured, a wheel stands on its spokes, be they wire, rope or pegs.

Thou protests too much.
There is no point to a diagram. Only those who wish to manipulate figures
and turn tension into compression to validate an improper method of
wheelbuilding feel a need to do this. The confusion lies in the figures.
It is diagrams with little arrows and numbers whose vectors do not add up
which confuse. And there no way on earth I will draw a 3D vector diagram
for something I can hold in my hands. The complication is the mask for JBs
method.
TJ

On Tue, 3 Aug 2004 00:26:19 +0100, "Trevor Jeffrey"
wrote:

One spoke without pre-tensioning is more than adequate to support my static
weight


Dear Trevor,

?

Carl Fogel

Trevor Jeffrey wrote:
Mark McMaster wrote in message ...

Sorry, it doesn't work this way. Because the spokes are far
stiffer than the rim, very little of the load is supported
by the rim at all when the wheel is loaded - at least not
until the spokes go slack. But then the wheel losses the
lateral stability you seek, so asking the rim to support the
load is a poor idea.


To what you are referring does not work I cannot make out. The spokes
are tensile members so need to be resistive to stretch and the rim is a
compressive member so needs to be resistive to squash. One is the complete
opposite of the other. The two are not comparable to each other. Aluminium
is good in compression but not in tension, this is the way of the world,
aluminium rims and steel spokes. If the rim did not support the load it
would not need to be there. It either does or it does not, extraneous items
are most usually omitted on a human powered vehicle. Rims are essential
part of the wheel and bear all the load. What else could possible transmit
the force between tyre and spokes?

As far as the role of the rim, it's main role is supply a
continuously round surface to mount the tire, to have a
sufficient compressive strength allow the spokes to be
pre-tensioned, and to have sufficient lateral strength to
bear the alternating side to side forces of the spokes on
each side of the wheel. For a wheel with a standard
compliments of spokes, the rim is not required to have any
strength to radial forces - it is the spokes, not the rim
that supports the radial load. If the rim were constructed
of many small hinged segments instead of being a continuous
arch, the wheel would still be able to support its load.

As I'm sure you'll agree, the compression on the rim is
caused by the spoke tension (i.e., the spokes pull radially
inward, attempting to circumferentially compress the rim).
If you had looked at the analyses of spoke tension changes
when a wheel is loaded more carefully, you would see that
the summation of the spoke tensions _decrease_ when a wheel
is loaded. In other words, there are large spoke tension
decreases directly at the bottom of the wheel, and only very
small spoke tension increases elsewhere around the rim. The
total sum of the spoke tension increases is far less than
the sum of the spoke tension decreases. Although there may
be some increases in rim compression around parts of the
wheel due to the small spoke tension increases, they are
very small.

If you are really concerned about rim compressive strength,
you should focus on braking forces - the only loading mode
that can add any substantial compression on the rim. This
is because this loading mode can apply a high load
tangential to the rim. Radial loads mostly apply the load
to the rim in bending - and since the spokes are so stiff,
as long as they remain in tension, the bending of the rim
will be minimized.

But you are an expert on wheels, so you knew all this.

Mark McMaster

wrote:

On Tue, 3 Aug 2004 00:26:19 +0100, "Trevor Jeffrey"
wrote:

One spoke without pre-tensioning is more than adequate to support my static
weight

Dear Trevor,

?

Carl Fogel

Trevor has obviously purchased a pair of Citroën Monospoke wheels from
Sheldon Brown.
http://www.sheldonbrown.com/nanodrive/index.html.

--
Tom Sherman – Quad City Area

In article ,
"Trevor Jeffrey" wrote:

Weisse Luft wrote in message ...
No, I am not confused. If you know how to draw a free body diagram,
you will see the error in your ways if you can accurately measure the
rim deflection.

Pretensioned structures easily confuse those who study them. Rest
assured, a wheel stands on its spokes, be they wire, rope or pegs.

Thou protests too much.
There is no point to a diagram. Only those who wish to manipulate figures
and turn tension into compression to validate an improper method of
wheelbuilding feel a need to do this. The confusion lies in the figures.
It is diagrams with little arrows and numbers whose vectors do not add up
which confuse. And there no way on earth I will draw a 3D vector diagram
for something I can hold in my hands. The complication is the mask for JBs
method.
TJ

Relative to the static state, yes, the bottom spokes undergo a
compression, but that compression is less than the tension already on
them, so they stay tensioned. Calling it compression instead of a
reduction of tension is six of one vs. a half dozen of the other.
Personally, I wouldn't say the bike stands on the bottom spokes as much
as it hangs from the top spokes. The rim supports the top spokes, and
the forward and trailing spokes hold the rim in shape. The bottom
spokes are just along for the ride. But mathematically, it's fine to
say it either way.
A free body diagram is handy for a structure you can hold in your
hands because you're not holding it in your hands when it's in use. In
its static state you can guesstimate about forces it'll experience, but
you don't just know without some calculations or experiments what
happens during a bump, high torque, or bending.
Anyway, the reason I always assumed for tensioning spokes has to do
with elasticity. Keep enough tension on them so that in the
loading/unloading cycle the experience as the wheel turns they never go
slack--they stretch enough to take up the movement. As the whole
structure moves around all parts remain in the same location relative to
each other and keep approximately the same loads they have when standing
still.
A similar application would be engine head bolts. They're
pre-tensioned (torqued to spec) to achieve a predetermined amount of
bolt stretch. That stretch more or less makes the bolts into springs
that can move a few hundred-thousandths when the engine fires. Without
the preload the bolts would move further and would repeatedly load and
unload, causing fatigue. It's impressive to watch a head bolt come
flying out of someone's hood.
Same with bicycle spokes--the springyness will hold all the parts in
place when the rim flexes, and keeping them loaded will prevent cyclical
unloading.
It happens with springs too--if you lighten a car enough without
lightening the suspension the springs can actually throw the car off the
tops of the springs, unloading them even if they're bolted in place with
clamps. Repeat that enough and the springs break far earlier than they
should even though the load on them is lighter.

--
B.B. --I am not a goat! thegoat4 at airmail.net

Trevor Jeffrey Wrote:
Weisse Luft wrote in message ...
No, I am not confused. If you know how to draw a free body diagram,
you will see the error in your ways if you can accurately measure the
rim deflection.

Pretensioned structures easily confuse those who study them. Rest
assured, a wheel stands on its spokes, be they wire, rope or pegs.

Thou protests too much.
There is no point to a diagram. Only those who wish to manipulate
figures
and turn tension into compression to validate an improper method of
wheelbuilding feel a need to do this. The confusion lies in the
figures.
It is diagrams with little arrows and numbers whose vectors do not add
up
which confuse. And there no way on earth I will draw a 3D vector
diagram
for something I can hold in my hands. The complication is the mask for
JBs
method.
TJ

Wheels stand on the spokes, plain and simple. If you load a wheel, you
will note the bottom spoke is the only spoke which significantly changes
its tension. That its tension decreases is the sign it is actually
taking a compressive load even though in the properly tensioned wheel,
this spoke never becomes fully slack. This is the fundamental element
of a prestressed structure.

Since you are bent in a Pol-Pot style condemnation of technical terms,
why don't you try the plucking test?


--
Weisse Luft

Dear Carl

??

Unless I know your assumptions, previous perception, I do not know how to
respond.
Do you think steel wire will take a tensile load more effectively if its
load is, say, doubled, in any way?

TJ
________
wrote in message ...
On Tue, 3 Aug 2004 00:26:19 +0100, "Trevor Jeffrey"
wrote:

One spoke without pre-tensioning is more than adequate to support my
static
weight


Dear Trevor,

?

Carl Fogel

Mark McMaster wrote in message ...
Trevor Jeffrey wrote:
Mark McMaster wrote in message ...

Sorry, it doesn't work this way. Because the spokes are far
stiffer than the rim, very little of the load is supported
by the rim at all when the wheel is loaded - at least not
until the spokes go slack. But then the wheel losses the
lateral stability you seek, so asking the rim to support the
load is a poor idea.


To what you are referring does not work I cannot make out. The
spokes
are tensile members so need to be resistive to stretch and the rim is a
compressive member so needs to be resistive to squash. One is the
complete
opposite of the other. The two are not comparable to each other.
Aluminium
is good in compression but not in tension, this is the way of the world,
aluminium rims and steel spokes. If the rim did not support the load it
would not need to be there. It either does or it does not, extraneous
items
are most usually omitted on a human powered vehicle. Rims are essential
part of the wheel and bear all the load. What else could possible
transmit
the force between tyre and spokes?

-------------------------+++++++++++++++++----------------------
As far as the role of the rim, it's main role is supply a
continuously round surface to mount the tire, /

INCORRECT The rim provides the rolling surface and the tyre reduces rolling
resistace and provides grip to assist traction. I consider a tyre should
also reduce jarring.

to have a
sufficient compressive strength allow the spokes to be
pre-tensioned,/

INCORRECT Spokes do not have to be pre-tensioned for a tensile spoked wheel
to function. The rim has to be able to withstand the compressive force
placed upon it in service. To enjoy lateral stability the nipples only
require winding to the point that no spoke comes loose(as in not in
contact ) from the rim or hub.

and to have sufficient lateral strength to
bear the alternating side to side forces of the spokes on
each side of the wheel. /

Not a problem with wheels using the method I describe.

For a wheel with a standard
compliments of spokes, the rim is not required to have any
strength to radial forces - it is the spokes, not the rim
that supports the radial load. If the rim were constructed
of many small hinged segments instead of being a continuous
arch, the wheel would still be able to support its load.

I'm glad someone has appreciated the function of an arch. I prefer to say
that the spokes restrain the rim in its arch and the spokes transfer the rim
loading to the hub. Further detail is not pertinent to the understanding of
an effective wheel build.


As I'm sure you'll agree, the compression on the rim is
caused by the spoke tension (i.e., the spokes pull radially
inward, attempting to circumferentially compress the rim). /

As I've pointed out above, the compressive load is caused by service and
that pre-loading the spokes is not required for a serviceable wheel. I
consider it is important not to take spoke tensioning further than that
which will result in a laterally stable wheel under reasonably expected
service conditions. Excessive tension in the spokes may cause the wheel to
self buckle with the slightest of knocks in service.

If you had looked at the analyses of spoke tension changes
when a wheel is loaded more carefully, you would see that
the summation of the spoke tensions _decrease_ when a wheel
is loaded. In other words, there are large spoke tension
decreases directly at the bottom of the wheel, and only very
small spoke tension increases elsewhere around the rim. The
total sum of the spoke tension increases is far less than
the sum of the spoke tension decreases. Although there may
be some increases in rim compression around parts of the
wheel due to the small spoke tension increases, they are
very small.

This is complex, innaccurate and irrelevant. It is absurd that you wish to
persuade that the spokes change tension to move the rim, the force on a
loaded wheel is generally in directions so as to bring together rim and hub
in the lower portion of the wheel. To suggest that the spokes act to move
the rim is incongruous of an inanimate object. The point is stated above,
the spokes transfer the load from the rim to the hub. I know not of which
analysis you seem to think I have looked at. If it suggests that which you
have indicated, it is worthless.


If you are really concerned about rim compressive strength,
you should focus on braking forces - the only loading mode
that can add any substantial compression on the rim. /

If you look again, you may find.

This
is because this loading mode can apply a high load
tangential to the rim./

You do not understand arches do you? Please ignore previous statement and
ammend to " I see you've heard of arches." All serviceable loads directed
through a wheel through the plane of that wheel will be restrained by the
rim. This is because the rim acts as an arch and changes the direction of
load through 90deg to travel along that arch.

Radial loads mostly apply the load
to the rim in bending - and since the spokes are so stiff,
as long as they remain in tension, the bending of the rim
will be minimized./

Adequately restrained arches do not bend significantly. The preforming of
the spoke at the crossing point, makes the rim adequetly restrained, without
the risk of self destructive forces otherwise encountered due to
overtensioning of spokes during construction. Spoke tension is kept to the
minimum required to maintain lateral stability under reasonably expected
service conditions.


But you are an expert on wheels, so you knew all this.


I now have a better understanding of your lack of knowledge.

TJ

Weisse Luft wrote in message ...

Wheels stand on the spokes, plain and simple. If you load a wheel, you
will note the bottom spoke is the only spoke which significantly changes
its tension. That its tension decreases is the sign it is actually
taking a compressive load even though in the properly tensioned wheel,
this spoke never becomes fully slack. This is the fundamental element
of a prestressed structure.

Since you are bent in a Pol-Pot style condemnation of technical terms,
why don't you try the plucking test?

I do not think the art of sophistry is conducive to understanding.
Spokes have no feet so cannot stand whether in a wheel or elsewhere.
A tensile spoked wheel does not mean a pre-tensioned wheel.
Tensile spoked means that the service load will be taken up by the spokes as
a tensile force. The spokes merely transfer the load between the hubshell
and the rim. The fact that spoke reduces in tension solely shows the
restraining elements have moved closer.
I'm satisfied with the amount of plucking I've done, thank you.
TJ

Weisse Luft wrote:

...
Since you are bent in a Pol-Pot style condemnation of technical terms,
why don't you try the plucking test?

Would not Trofim Denisovich Lysenko be a better example than "Brother
No. 1"?

--
Tom Sherman – Quad City Area