Bicycle wheels - how do they work?

Pyromancer said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work?

It's not a silly question, it's a very complex question.

Quoted message said:

load supported by the seemingly impossibly thin spokes? Does the load
mainly hang from the upper ones, or is it supported in compression on
the lower lot? A mixture of both, or are they all in tension?

All in tension, but some more than others..

Buy a copy of Jobst Brandt's "The Bicycle Wheel", which will not only
give you the stress analysis of the wheel's component parts, but also
instruct you on how to build them.

Mike

Pyromancer said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work? How is
the load supported by the seemingly impossibly thin spokes? Does the
load mainly hang from the upper ones, or is it supported in
compression on the lower lot? A mixture of both, or are they all in
tension?

They are all in tension.

This subject has been discussed before in great detail here and on
rec.bicycles.tech. Please have a butcher's via Google Groups.

~PB

in message <[email hidden]>, Pyromancer

(') said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work? How is
the
load supported by the seemingly impossibly thin spokes? Does the load
mainly hang from the upper ones, or is it supported in compression on
the lower lot? A mixture of both, or are they all in tension?

Beware: this is a profoundly religious argument, which will make helmet
flame wars look like mild disagreements between old friends. In
particular, do not ask this question on rec.bicycles.tech. If you would
like to know what happens if you do, check on google.

I give you warning, the debate gives rise to a lot more heat than light.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Anagram: I'm soon broke.

"Pyromancer" <[email hidden]> wrote

Quoted message said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work? How is the
load supported by the seemingly impossibly thin spokes? Does the load
mainly hang from the upper ones, or is it supported in compression on
the lower lot? A mixture of both, or are they all in tension?

Bicycle wheel spokes are tensioned on assembly. Presumably the idea is to
keep them that way under load.
How does a wheel with an infinite number of spokes work, such as on a 2CV?

in message <[email hidden]>, DavidR

('david.nospam.r_a@t_cwcom.net') said:

"Pyromancer" <[email hidden]> wrote

Quoted message said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work? How is
the
load supported by the seemingly impossibly thin spokes? Does the
load mainly hang from the upper ones, or is it supported in
compression on
the lower lot? A mixture of both, or are they all in tension?

Bicycle wheel spokes are tensioned on assembly. Presumably the idea is
to keep them that way under load.
How does a wheel with an infinite number of spokes work, such as on a
2CV?

Eh? All the tin snails I've ever seen had pressed steel wheels.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

I'm fed up with Life 1.0. I never liked it much and now it's getting
me down. I think I'll upgrade to MSLife 97 -- you know, the one that
comes in a flash new box and within weeks you're crawling with bugs.

On Thu, 30 Sep 2004 08:35:09 GMT, Simon Brooke <[email hidden]>

Quoted message said:

Quoted message said:

How does a wheel with an infinite number of spokes work, such as on a
2CV?

Eh? All the tin snails I've ever seen had pressed steel wheels.

That's presumably the point - a disk can be regarded as an infinite
number of spokes.

Except that it can't be, because there's no pre-stressing and the
"spokes" are coupled to their neighbours. So really it's a useless
analogy.

Pyromancer said:

how do the wheels actually work?

The tensioned spokes spend their time trying to arm-wrestle the rim
into collapse. Normally the rim (a hoop) is good at resisting this,
because arches like that are strong. If you pringle the rim though, it
collapses suddenly.

When you weight the axle, you reduce the pre-load on the lower spokes.
If this is enough to make them go slack, then you have a weak wheel
where the unsupported rim will collapse under the first external
impact. So combined spoke tension needs to be substantially more than
the useful load capacity of the wheel.

Jobst's book is the best resource around on the theory of wheels. But
Sheldon's site has enough (so long as you're happy to accept a few
axioms) and it has better instructions on how to build them.

--
Smert' spamionam

DavidR said:

"Pyromancer" <[email hidden]> wrote

Quoted message said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work? How

is the

Quoted message said:

Quoted message said:

load supported by the seemingly impossibly thin spokes? Does the

load

Quoted message said:

Quoted message said:

mainly hang from the upper ones, or is it supported in compression

on

Quoted message said:

Quoted message said:

the lower lot? A mixture of both, or are they all in tension?

Bicycle wheel spokes are tensioned on assembly. Presumably the idea

is to

Quoted message said:

keep them that way under load.
How does a wheel with an infinite number of spokes work, such as on a

2CV?

Hi there.

If by an infinite number of spokes you mean a solid wheel, then it
works in a whole different way.

My aero disc wheel acts as a single body under compression, which is a
lot less efficient use of material than a spoked wheel. It weighs more
than my spoked wheels, and it is very stiff and uncomfortable - which
makes it skip out sideways under hard cornering. But it is fast...
Cheers, Andy
www.stirling-tri.co.uk

Pyromancer said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work? How is the
load supported by the seemingly impossibly thin spokes? Does the load
mainly hang from the upper ones, or is it supported in compression on
the lower lot? A mixture of both, or are they all in tension?

They are all always in tension (at least until collapse) - the spoke
mounting method with a flanged nipple can't conduct any compression
into teh spoke. However, the load-carrying effects are all
concentrated in teh lower spokes.

Thus, teh argument is predominantly one of semantics - is it fair to
say teh hub stands on spokes which are in tension? Is it fair to say
the hub hangs from something below teh hub?

Personally, I favour saying that since the load-resisting effects are
in teh spokes between teh hub and the road, it is reasonable to
describe this as the hub standing on teh lower spokes. Some people
maintain it's impossible to say this because the lower spokes are in
tension, so can't be 'standing on' must be 'hanging from'. I can't
imagine hanging from something below me, and presume these people have
never stood on the main cable of a suspension bridge.

There are some finite element analyses I did (mainly to fend off
rustiness with a particular FE program) on my web site at
http://www.astounding.org.uk/ian/wheel/ pretty pictures, graphs and
things.

One concept to make sure you have a firm grasp of when thinking about
such things is that of 'statically indeterminate'. This means whether
or not you can calculate the beahiviour of teh structure without
knowing the relative stiffness of the components. A tensioned spoke
wheel is statically indeterminate, and behaves in different ways if
you change the stiffnesses. This means that thought experiments that
start with "imagine if all the spokes were elastic bands..." are
complete baloney, irrelevant unless very carefully formulated, and
normally teh work of someone who doesn't really understand teh issue.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

In article said:

Personally, I favour saying that since the load-resisting effects are
in teh spokes between teh hub and the road, it is reasonable to
describe this as the hub standing on teh lower spokes. Some people
maintain it's impossible to say this because the lower spokes are in
tension, so can't be 'standing on' must be 'hanging from'. I can't
imagine hanging from something below me, and presume these people have
never stood on the main cable of a suspension bridge.

Standing on the main cable of a suspension bridge puts your leg in
compression, and doesn't decrease the tension in the cable, so it
isn't really comparable.

(I personally think that "standing on" is also reasonable shorthand for
what happens, and as accurate as any equally succinct description, but
repeat the recommendation that the original poster Google for previous
discussions, where they will find people who understand what happens
arguing fiercely about the best way to describe it, along with people
who don't understand muddying the issue. The continued existence of the
latter after lots of debate amongst the former suggests that there is no
short simple easy to understand correct description. ("Read Jobst's book"
isn't a description itself, it's a short simple easy to understand correct
way to find a description which is quite long.)

in message <[email hidden]>, Ian Smith

(') said:

On Wed, 29 Sep, Pyromancer <[email hidden]>

Quoted message said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work?  How is
the load supported by the seemingly impossibly thin spokes?  Does the
load mainly hang from the upper ones, or is it supported in
compression on the lower lot?  A mixture of both, or are they all in
tension?

They are all always in tension (at least until collapse) - the spoke
mounting method with a flanged nipple can't conduct any compression
into teh spoke.  However, the load-carrying effects are all
concentrated in teh lower spokes.

I know this is the great Jobst Brandt's [to whom all bow] great thesis.
but I do not buy it. Take all the spokes out of the upper part of the
wheel and it will collapse. Ergo, the spokes in the upper part of the
wheel are contributing to the load carrying effect of the whole wheel.
This reductionist notion that you can consider independent members of a
tension structure in isolation, and say that 'the work' (or 'the load
carrying effects'😉 are entirely due to one or another is hokum, in my
opinion. While there is arguably a certain amount of redundancy in a 36
spoke wheel, every component contributes to the load carrying ability
of the whole all of the time.

The whole 'stands on/hangs from' debate isn't merely semantic, it's also
orthogonal to the point.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Pyromancer said:

Quoted message said:

[snip]
<-- The Gothic Revival.

Isn't a gothic revival the last thing the world needs? Lots of men
wearing make-up and sulking all the time...

Zardoz said:

Pyromancer said:

Quoted message said:

[snip]
<-- The Gothic Revival.

Isn't a gothic revival the last thing the world needs? Lots of men
wearing make-up and sulking all the time...

What people do in the privacy of their...

Anyway, the Gothic Revival site's useful because it tells us this:

"My name is Jack, aka Pyromancer, pagan, partnered, and under the spell of
the Darkside."

So, at least he's prepared to come out of the closet regarding his cycling
habits.

Colin

On 30/9/04 12:35 pm, in article
[email hidden], "Simon Brooke"

Quoted message said:

The whole 'stands on/hangs from' debate isn't merely semantic, it's also
orthogonal to the point.

No, that would be the axle...

...d

Simon Brooke said:

in message <[email hidden]>, Ian Smith

(') said:

On Wed, 29 Sep, Pyromancer <[email hidden]>

Quoted message said:

Ok, this may seem like a silly question, but cycling home tonight I
found myself wondering just how do the wheels actually work?  How is
the load supported by the seemingly impossibly thin spokes?  Does the
load mainly hang from the upper ones, or is it supported in
compression on the lower lot?  A mixture of both, or are they all in
tension?

They are all always in tension (at least until collapse) - the spoke
mounting method with a flanged nipple can't conduct any compression
into teh spoke.  However, the load-carrying effects are all
concentrated in teh lower spokes.

I know this is the great Jobst Brandt's [to whom all bow] great thesis.
but I do not buy it. Take all the spokes out of the upper part of the
wheel and it will collapse. Ergo, the spokes in the upper part of the
wheel are contributing to the load carrying effect of the whole wheel.

The simplified explanation does not claim otherwise. To say that teh
load carrying effects are concentrated in teh lower spokes does not
say that the upper spokes are therefore redundant, any more than it
says the rim is redundant, or that teh road is redundant.

Your sentence preceeding the 'ergo' is verging on straw-man territory.

Take all the spokes out of teh upper part, and it will collapse
_before_any_load_is_applied_, so teh collapsy-ness due to missing
upper spokes is not of itself relevant to behaviour under load - by
means of a fairly simple cause-and-effect train of thought.

Quoted message said:

This reductionist notion that you can consider independent members of a
tension structure in isolation, and say that 'the work' (or 'the load
carrying effects'😉 are entirely due to one or another is hokum, in my
opinion. While there is arguably a certain amount of redundancy in a 36
spoke wheel, every component contributes to the load carrying ability
of the whole all of the time.

No-one (that I know of) has claimed otherwise. No-one has claimed the
load carrying is "entirely due to" teh lower spokes. However, the
load carrying effects _are_ concentrated in teh lower spokes.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

Quoted message said:

Hi there.

If by an infinite number of spokes you mean a solid wheel, then it
works in a whole different way.

My aero disc wheel acts as a single body under compression

Are you sure?

BugBear

mae <[email hidden]> wedi ysgrifennu:

Quoted message said:

Isn't a gothic revival the last thing the world needs? Lots of men
wearing make-up and sulking all the time...

The last thing the world needs is an invasion of vampire insect creatures
from Venus spitting acid and destroying everything in their path.

The second last thing is the re-election of George W. Bush.

The goff revival comes third on the list.

--
Rob

Please keep conversations in the newsgroup so that all may contribute
and benefit.

Simon Brooke said:

I know this is the great Jobst Brandt's [to whom all bow] great thesis.
but I do not buy it. Take all the spokes out of the upper part of the
wheel and it will collapse. Ergo, the spokes in the upper part of the
wheel are contributing to the load carrying effect of the whole wheel.

Of course they are an important part of the structure, but the point of
the "stands on the lower spokes" description is that it succinctly and
accurately explains the behaviour of a loaded wheel - that is, it is
only the lower spokes that are (significantly) affected by the load, and
the limiting load is that at which the lower spokes go completely slack
(near enough). Just saying that the wheel is a complex structure which
must be considered as a whole does not have any explicative power.
Saying it stands on the lower spokes gets you at least half-way to
understanding how it behaves.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

Ian Smith said:

Thus, the argument is predominantly one of semantics - is it
fair to say the hub stands on spokes which are in tension? Is
it fair to say the hub hangs from something below the hub?

Personally, I favour saying that since the load-resisting
effects are in the spokes between the hub and the road, it is
reasonable to describe this as the hub standing on the lower
spokes. Some people maintain it's impossible to say this
because the lower spokes are in tension, so can't be 'standing
on' must be 'hanging from'. I can't imagine hanging from
something below me, and presume these people have never stood
on the main cable of a suspension bridge.

I'm a glutton for punishment, so here goes......

The usual FEA splits the rim into 36 elements each containing a spoke. Your
version is in agreement with several others published on the web, so lets
take the numbers as being correct, within the usual modelling errors. The
models are also in agreement with empirical observations of changes in spoke
tensions on a real wheel.

See if this makes sense..... and read it several times before replying!

Instead of 36, split the rim into 72 elements: 36 with a spoke, 36 without.
(I know that in computational terms that is a daft over complicating thing
to do, but conceptually it is valid)

Rotate the wheel such that one of the unspoked elements is in contact with
the ground.

Load the hub.

Examine the forces acting on the element in contact with the ground.

* Up forces: Normal reaction only.

* Down forces: vertical component of Compression vectors from the adjacent
elements only

ie the load through the hub is carried by rim compression.

Now, because the system is statically indeterminate, any change in rim
compression must be reflected in changes in spoke tensions. By the nature of
the system, the actual change in rim compression is small as the effect is
mitigated by the spokes.

Just how the tensions change depends on the various coefficients of rim and
spokes, but the basic physics is the same. The extra loading of the rim
causes the rim to flex slightly which causes the lower spokes to shorten
slightly which results in reduced tension in the lower spokes

In summary:

The load is carried neither by hanging from nor standing on spokes. Rather,
the nature of a pretensioned wheel is such that loading the hub reduces the
tension in the lower spokes with minimal changes either in rim compression
or in the tension of other spokes.

The whole problem in trying to understand what happens is a double layer of
counter intuition:
Wrong intuition number 1: It's obvious, the hub must hang from the upper
spokes as the lower spokes cannot act in compression.
Wrong intuition number 2: So, if it doesn't hang it must stand!

Sense or bollocks?

pk