A physicist's question about tensioning a wheel
Sergio SERVADIO
Why so?
By turning the nipples a little bit more we effectively shorten the rest
length of the spokes, not changing a bit their elastic constant .
Now, a change of anyone of the rest lengths of an elastic system does not
change at all its elastic constant/s, but changes only its rest
configuration when under no load [the elastic quadratic coefficient
does not change].
So, by turning nipples a bit more or a bit less, barring the possibility
of having spokes go slack, the wheel should remain just as stiff.
So, the questions.
Am I totally wrong?
Or, is it that we are exploiting the non-elasticity [non linear in fact]
of some component of the wheel?
Which one: the spokes or the rim?
Sergio
Pisa
dianne_1234
<serv...@mail.df.unipi.it> wrote:
>The higher the spokes' tension the stiffer the wheel, of course.
>Why so?
The data I know of do not support that assumption.
Take a few quick measurements. Here's one way:
http://www.sheldonbrown.com/rinard/wheel/index.htm
First, I hope you can suggest a way to get better repeatability in
measuring the stiffness of wheels. On this site
http://www.sheldonbrown.com/rinard/wheel/index.htm#3 there appears to
be some variation, up to about 0.007". Maybe that is part of the
roughness of the rim side wall where the dial indicator takes the
reading?
Second, a bit further up the page at
http://www.sheldonbrown.com/rinard/wheel/index.htm#1 the wheel appears
to become slightly stiffer with decreasing spoke tension, the opposite
of your assumption. But I don't believe those measurements reflect any
significant trend. Is the variation in that data supported by the
reported variation in the measurements at #3 above? I don't know how
to determine that.
My strategy: I don't consider wheel stiffness while tensioning; I make
spoke tension high for good wheel strength.
Sergio SERVADIO
> On Sat, 3 Jan 2004 07:51:25 +0100, Sergio SERVADIO
> <serv...@mail.df.unipi.it> wrote:
> >The higher the spokes' tension the stiffer the wheel, of course.
> >Why so?
> The data I know of do not support that assumption.
Well, thank you.
You are saying that I had a wrong assumption in the back of my mind.
One of those I must have picked up without thinking too much.
No wonder I could not 'explain' why it should be so.
I tell you, I feel elated!
Thanks again
Sergio
Pisa
Tim McNamara
> The higher the spokes' tension the stiffer the wheel, of course.
Bracing angle of the spokes. However, bicycle wheels are not very
stiff laterally and are very stiff radially. This is OK because the
wheels rarely see a significant lateral load.
Simon Brooke
I don't know, but I'd like to add one completely surprising
observation. Among the bikes in this household is a twenty year old
Raleigh Royale with 27" wheels which, until this year, hadn't been
ridden for about six years (it was my sister's; she died). The rear
wheel is original. All the spokes are quite noticably slack - you can
take any individual spoke and rattle it. But the wheel is reasonably
true - true enough not to rub on the brakes or interfere with the
mudguard. I'm so surprised at this that I've left it that way to see
what will happen, and what has happened is... precisely nothing. It's
been ridden for over 400 miles over the past three months in this
state, and the wheel is still adequately true. Sooner or later of
course I'm going to have to take it out and tension it because apart
from anything else it just doesn't look right... but I'm amazed that
it has remained usable.
Twenty years ago it was a reasonable wheel; the Royale was one of the
more upmarket Raleighs (531c tubing, etc). It's an aluminium rim
marked 'WEINMANN Made in Belgium'. It's not a specially strong or
stiff rim.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; Life would be much easier if I had the source code.
Chris B.
wrote:
Since you have argued here extensively about how how ridiculous the
notion is that the bottom spokes compress and carry almost all of the
load, your loosely spoked wheel must be quite strong by your reckoning
(from the point of view of tensile overload in the upper spokes) and
indeed you are here saying it works fine.
Go with it!
Pete Biggs
> I'd like to add one completely surprising
> observation. Among the bikes in this household is a twenty year old
> Raleigh Royale with 27" wheels which, until this year, hadn't been
> ridden for about six years (it was my sister's; she died). The rear
> wheel is original. All the spokes are quite noticably slack - you can
> take any individual spoke and rattle it. But the wheel is reasonably
> true - true enough not to rub on the brakes or interfere with the
> mudguard. I'm so surprised at this that I've left it that way to see
> what will happen, and what has happened is... precisely nothing. It's
> been ridden for over 400 miles over the past three months in this
> state, and the wheel is still adequately true. Sooner or later of
> course I'm going to have to take it out and tension it because apart
> from anything else it just doesn't look right... but I'm amazed that
> it has remained usable.
You're likely to get broken spokes through metal fatigue if you continue
with them slack.
~PB
Sheldon Brown
> I'd like to add one completely surprising
> observation. Among the bikes in this household is a twenty year old
> Raleigh Royale with 27" wheels which, until this year, hadn't been
> ridden for about six years (it was my sister's; she died). The rear
> wheel is original. All the spokes are quite noticably slack - you can
> take any individual spoke and rattle it. But the wheel is reasonably
> true - true enough not to rub on the brakes or interfere with the
> mudguard. I'm so surprised at this that I've left it that way to see
> what will happen, and what has happened is... precisely nothing. It's
> been ridden for over 400 miles over the past three months in this
> state, and the wheel is still adequately true. Sooner or later of
> course I'm going to have to take it out and tension it because apart
> from anything else it just doesn't look right... but I'm amazed that
> it has remained usable.
>
> Twenty years ago it was a reasonable wheel; the Royale was one of the
> more upmarket Raleighs (531c tubing, etc). It's an aluminium rim
> marked 'WEINMANN Made in Belgium'. It's not a specially strong or
> stiff rim.
It probably has carbon-steel spokes, as did most bikes back then.
Although carbon-steel spokes are not as strong as stainless (and prone
to rusting) they are less subject to fatigue than stainless spokes are.
Loosely spoked wheels were the norm on production bikes back then, and
manufacturers relied on using plenty of spokes and fairly (or very)
rigid rims.
Your wheel may give good service for a long time if used with care, but
the loose spokes will make it less resistant to getting dented inward,
by potholes, kerbs and the like. If you manage to avoid such road
hazards, it should be OK.
Sheldon "Stainless" Brown
+--------------------------------------------+
| Life is what happens to you, |
| while you're busy making other plans. |
| --John Lennon |
+--------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
jobst....@stanfordalumni.org
>> I'd like to add one completely surprising observation. Among the
>> bikes in this household is a twenty year old Raleigh Royale with
>> 27" wheels which, until this year, hadn't been ridden for about six
>> years (it was my sister's; she died). The rear wheel is
>> original. All the spokes are quite noticeably slack - you can take
>> any individual spoke and rattle it. But the wheel is reasonably
>> true - true enough not to rub on the brakes or interfere with the
>> mudguard. I'm so surprised at this that I've left it that way to
>> see what will happen, and what has happened is... precisely
>> nothing. It's been ridden for over 400 miles over the past three
>> months in this state, and the wheel is still adequately
>> true. Sooner or later of course I'm going to have to take it out
>> and tension it because apart from anything else it just doesn't
>> look right... but I'm amazed that it has remained usable.
> You're likely to get broken spokes through metal fatigue if you
> continue with them slack.
I read this admonition now and then and have not heard an explanation
of how slack spokes cause fatigue failures. More likely loose spokes
will cause wheel collapse at some inopportune moment where an awkward
side load is encountered. I have ridden with light weight riders
whose spokes rattled for many miles before the noise got to the point
that I trued and tensioned his wheel. He was a good hill climber so I
dod not have theoption of riding off ahead where I didn''t need to
listen to it. These wheels dis not suffer form the looseness although
other that I observed collpased.
Jobst Brandt
jobst....@stanfordalumni.org
Paul
> All the spokes are quite noticeably slack - you can
> take any individual spoke and rattle it.
An interesting observation that, Simon. I take it you mean when the bike was
unloaded all the spokes rattled.
Worth repeating.
> All the spokes are quite noticeably slack - you can
> take any individual spoke and rattle it.
How do you suppose the load on the hub was supported when the slack spokes
were at the bottom?
paul
Fred Clydesdale
jobst....@stanfordalumni.org
> All the spokes are quite noticeably slack - you can take any
> individual spoke and rattle it.
Next time get on the bicycle and have someone else test which spokes
are slack. You'll discover that most of the spokes are tight when you
put a load on the wheel. Only the ones near the bottom will be slack,
which of course means you don't have a laterally stable wheel. It can
wiggle from side to side and, if you give it a side load, will
collapse. This is not what is known as a "whole" wheel. It's on the
verge of collapse and, as you say, is not a tensioned spoked wheel.
Don't expect it to respond to loads the way a tensioned wheel does.
Jobst Brandt
jobst....@stanfordalumni.org
Simon Brooke
> Simon Brooke wrote:
>
> > All the spokes are quite noticeably slack - you can
> > take any individual spoke and rattle it.
>
>
> An interesting observation that, Simon. I take it you mean when the bike was
> unloaded all the spokes rattled.
Yes.
> Worth repeating.
>
> > All the spokes are quite noticeably slack - you can
> > take any individual spoke and rattle it.
>
> How do you suppose the load on the hub was supported when the slack spokes
> were at the bottom?
Why, it was standing on them of course. The Great Jobst has said so,
how can any further comment be other than superfluous? If there is any
difference between reality and the pronouncements of the Great Jobst,
it is always reality which is wrong.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; gif ye hes forget our auld plane Scottis quhilk your mother lerit you,
;; in tymes cuming I sall wryte to you my mind in Latin, for I am nocht
;; acquyntit with your Southeron
;; Letter frae Ninian Winyet tae John Knox datit 27t October 1563
B.C. Cletta
> The higher the spokes' tension the stiffer the wheel, of course.
> Why so?
maybe not.
physicist? remember that spring thing?: hang a weight 'W' on a
spring, it extends 'x'. hang a 2nd W on, it extends another 'x'. the
1st W, preload if you will, don't change the response from the 2nd W.
jim beam
<snip>
>
> I don't know, but I'd like to add one completely surprising
> observation. Among the bikes in this household is a twenty year old
> Raleigh Royale with 27" wheels which, until this year, hadn't been
> ridden for about six years (it was my sister's; she died). The rear
> wheel is original. All the spokes are quite noticably slack - you can
> take any individual spoke and rattle it. But the wheel is reasonably
> true - true enough not to rub on the brakes or interfere with the
> mudguard. I'm so surprised at this that I've left it that way to see
> what will happen, and what has happened is... precisely nothing. It's
> been ridden for over 400 miles over the past three months in this
> state, and the wheel is still adequately true. Sooner or later of
> course I'm going to have to take it out and tension it because apart
> from anything else it just doesn't look right... but I'm amazed that
> it has remained usable.
my mother used to go shopping on a bike like that and would come home
/loaded/ with groceries. dare i say it, she was no bantam weight
either. this bike used to get ridden most days of the week. loose
spokes, just like you say.
then one day, just as she was pulling up in front of our house, the rear
wheel started to collapse. it was a bit like watching a mime comedian
walking down an imaginary staircase - she just sunk lower & lower as she
rolled along with more & more spokes giving up the ghost. father got
her another wheel but she never rode it again.
as i recall, the wheel was never superbly true, but was not bad either.
the spokes would kind of rattle. considering the use it had, i think
it had lasted quite well. 50's vintage?
jb
jim beam
<snip>
>
> It probably has carbon-steel spokes, as did most bikes back then.
> Although carbon-steel spokes are not as strong as stainless (and prone
> to rusting) they are less subject to fatigue than stainless spokes are.
the carbon alloy steel spokes were galvanized most likely. flashy
[literally] ones were chrome plated.
technically, carbon alloy steel wire is usually stronger than stainless.
it's still used in steel rope where strength [&/or price] outweighs
weather considerations.
carbon steel spokes /were/ less prone to fatigue. modern stainless
steels are significantly better than they used to be and now the two are
roughly comparable. high strength carbon alloy steels do not typically
have a fatigue endurance limit - it's just that it's been possible to
make "cleaner" carbon alloy steels [cheaper] longer than has been
possible for stainless.
if ever you travel to san francisco, there are two pieces of interesting
wire that you must see:
one is at the golden gate bridge. there is a section of the main span
rope cut open for inspection at the visitor center. interesting
un-twisted strand design. high strength carbon alloy steel.
the other is the crowd barrier rope at the cable car turnaround on
powell & market. it's a piece of actual cable car traction rope.
unlike all the [wire] rope you normally see that is twisted to make the
exterior strands run axially, this one is twisted to make the exterior
stranding as close to perpendicular as possible. this is to give
maximum possible friction for the cable car's rope clutching mechanism
as it goes up the hills. again, carbon alloy steel.
/utterly/ useless trivia, but thrillingly geeky!
jb
Phil Holman
"Simon Brooke" <si...@jasmine.org.uk> wrote in message
news:87d6a0h...@gododdin.internal.jasmine.org.uk...
> "Paul" <pnew...@hotmail.com> writes:
>
> > Simon Brooke wrote:
> >
> > > All the spokes are quite noticeably slack - you can
> > > take any individual spoke and rattle it.
> >
> >
> > An interesting observation that, Simon. I take it you mean when the
bike was
> > unloaded all the spokes rattled.
>
> Yes.
>
> > Worth repeating.
> >
> > > All the spokes are quite noticeably slack - you can
> > > take any individual spoke and rattle it.
> >
> > How do you suppose the load on the hub was supported when the slack
spokes
> > were at the bottom?
>
> Why, it was standing on them of course. The Great Jobst has said so,
> how can any further comment be other than superfluous? If there is any
> difference between reality and the pronouncements of the Great Jobst,
> it is always reality which is wrong.
"The power of accurate observation is called cynicism
by those who have not got it." - G. B. Shaw
Phil Holman
jobst....@stanfordalumni.org
>> I don't know, but I'd like to add one completely surprising
>> observation. Among the bikes in this household is a twenty year
>> old Raleigh Royale with 27" wheels which, until this year, hadn't
>> been ridden for about six years (it was my sister's; she died).
>> The rear wheel is original. All the spokes are quite noticeably
>> slack - you can take any individual spoke and rattle it. But the
>> wheel is reasonably true - true enough not to rub on the brakes or
>> interfere with the mudguard. I'm so surprised at this that I've
>> left it that way to see what will happen, and what has happened
>> is... precisely nothing. It's been ridden for over 400 miles over
>> the past three months in this state, and the wheel is still
>> adequately true. Sooner or later of course I'm going to have to
>> take it out and tension it because apart from anything else it just
>> doesn't look right... but I'm amazed that it has remained usable.
> My mother used to go shopping on a bike like that and would come
> home /loaded/ with groceries. Dare I say it, she was no bantam
> weight either. This bike used to get ridden most days of the week.
> Loose spokes, just like you say.
> Then one day, just as she was pulling up in front of our house, the
> rear wheel started to collapse. It was a bit like watching a mime
> comedian walking down an imaginary staircase - she just sunk lower &
> lower as she rolled along with more & more spokes giving up the
> ghost. Father got her another wheel but she never rode it again.
That's a nice story but I think you are reconstructing the event from
imagination. Wheels cannot slowly sink to a lower rolling diameter.
The failure mode is lateral collapse and that jams the wheel in the
frame so it won't turn. It makes a nice story but it didn't happen.
> As I recall, the wheel was never superbly true, but was not bad
> either. The spokes would kind of rattle. Considering the use it
> had, I think it had lasted quite well. 50's vintage?
I suppose the upshot is that "we don't need no steenkin tension in our
wheels". I see no other reason for these testimonials, phony as they
sound to wheelbuilders. Loose wheels can be ridden but it isn't a
reasonable thing to do if you know the wheel is rattlingly loose.
That such a wheel is true is an old story, something on which inept
wheel builders rely, because they don't know how to true a wheel once
the spokes are tight enough to overcome the original trueness of a new
rim. New rims are true and remain that way in the absence of spoke
tension. This should not be amazing. What is amazing is that some
people ride so timidly that their wheels rarely see much stress for
which they would need to demonstrate strength, strength that depends
primarily on spoke tension, if there is any.
Jobst Brandt
jobst....@stanfordalumni.org
Ron Hardin
> So, the questions.
> Am I totally wrong?
> Or, is it that we are exploiting the non-elasticity [non linear in fact]
> of some component of the wheel?
> Which one: the spokes or the rim?
The tensioning creates stiffness side-to-side by preventing even the
slackest spoke from going slack. The spokes work in pairs side to side,
the one taking up tension and the other losing it, as a side-to-side restoring
force. Once one stops losing tension because it's finally loose, additional restoring
force is partly missing.
--
Ron Hardin
rhha...@mindspring.com
On the internet, nobody knows you're a jerk.
jobst....@stanfordalumni.org
>> It probably has carbon-steel spokes, as did most bikes back then.
>> Although carbon-steel spokes are not as strong as stainless (and
>> prone to rusting) they are less subject to fatigue than stainless
>> spokes are.
> The carbon alloy steel spokes were galvanized most likely. Flashy
> [literally] ones were chrome plated.
> Technically, carbon alloy steel wire is usually stronger than
> stainless. It's still used in steel rope where strength [&/or
> price] outweighs weather considerations.
If exposed to weather, such cables are galvanized and often painted to
protect them from rusting. This is mostly a matter of cost, stainless
cables being far more expensive than carbon steel.
> Carbon steel spokes /were/ less prone to fatigue. Modern stainless
> steels are significantly better than they used to be and now the two
> are roughly comparable. High strength carbon alloy steels do not
> typically have a fatigue endurance limit - it's just that it's been
> possible to make "cleaner" carbon alloy steels [cheaper] longer than
> has been possible for stainless.
> If ever you travel to San Francisco, there are two pieces of
> interesting wire that you must see:
> One is at the golden gate bridge. There is a section of the main
> span rope cut open for inspection at the visitor center.
> Interesting un-twisted strand design. High strength carbon alloy
> steel.
You will notice that these "cables" are completely encased in a
waterproof steel jacket and are in real life pumped solidly full of
grease like preservative... as they are on most suspension bridges.
The suspenders on the GG Bridge are exposed strands but are helically
wound and are galvanized and painted with the traditional red paint of
that bridge. What is less evident to the casual observer is that
because the bridge lives in fog and salt spray, it does not have
exposed riveted lattice-work as other bridges around the bay. It's
towers are enclosed so the structural elements within the towers can
be kept dry and clean.
> The other is the crowd barrier rope at the cable car turnaround on
> Powell & Market. It's a piece of actual cable car traction rope.
> Unlike all the [wire] rope you normally see that is twisted to make
> the exterior strands run axially, this one is twisted to make the
> exterior stranding as close to perpendicular as possible. This is
> to give maximum possible friction for the cable car's rope clutching
> mechanism as it goes up the hills. Again, carbon alloy steel.
Since these cables bend around pulleys and curves, they must be
helically wound or they would break immediately. They are made this
way for the same reason control cables on bicycles are helically
wound... so they will have uniform stress in all strands when bending
around curves. Cable car cable has a special layer of external
friction strands that are smooth and rectangular, like the ones for
aerial trams where cables are sued as rails on which the tram rides.
This is done to reduce wear that would occur if the outer strands had
a round cross section or even themselves made of strands, as are old
Campagnolo bar-end shift cables.
> /utterly/ useless trivia, but thrillingly geeky!
http://www.cablecarmuseum.com/Anat/Anat.html
Don't pass along myth and lore.
Jobst Brandt
jobst....@stanfordalumni.org
Ryan Cousineau
jim beam <u...@ftc.gov> wrote:
Don't forget to visit the cable car museum, too. When I first looked at
the cable car system I couldn't figure out what was going on underneath
the road to get acceleration and braking. Any system I could crudely
guess at seemed to be destined to have a huge amount of wear.
The museum explained it: the cable grip jaws get replaced every four
days on average.
http://www.cablecarmuseum.com/Anat/Anat.html
> /utterly/ useless trivia, but thrillingly geeky!
The whole cable car system is an amazing exercise in high-wear parts:
the grip jaws wear quickly, the cable gets replaced frequently, the
brakes wear out fast. If it wasn't for tourism, the whole wonderful
thing would be deader than dead.
The 3-day Muni pass, BTW, is a great deal if you like riding the cable
cars.
--
Ryan Cousineau, rcou...@sfu.ca http://www.sfu.ca/~rcousine
President, Fabrizio Mazzoleni Fan Club
Pete Biggs
> Pete Biggs writes:
>> You're likely to get broken spokes through metal fatigue if you
>> continue with them slack.
>
> I read this admonition now and then and have not heard an explanation
> of how slack spokes cause fatigue failures.
I thought fatigue was caused by spokes repeatedly going from slack to taut
and that the slacker the spokes, the more difference in tension there
would be in use.
"A spoked wheel relies on having all of the spokes in constant tension. A
highly dished rear wheel starts with very light tension on the left side
spokes. The torque of hard pedaling can cause the left side "leading"
spokes to occasionally go completely slack momentarily. Repeated cycles of
tension and slackness cause these spokes to fatigue at the bends, and
ultimately break."
- www.sheldonbrown.com/wheelbuild.html
~PB
Chris B.
wrote:
>"Paul" <pnew...@hotmail.com> writes:
>
>> Simon Brooke wrote:
>>
>> > All the spokes are quite noticeably slack - you can
>> > take any individual spoke and rattle it.
>>
>>
>> An interesting observation that, Simon. I take it you mean when the bike was
>> unloaded all the spokes rattled.
>
>Yes.
>
>> Worth repeating.
>>
>> > All the spokes are quite noticeably slack - you can
>> > take any individual spoke and rattle it.
>>
>> How do you suppose the load on the hub was supported when the slack spokes
>> were at the bottom?
>
>Why, it was standing on them of course. The Great Jobst has said so,
>how can any further comment be other than superfluous? If there is any
>difference between reality and the pronouncements of the Great Jobst,
>it is always reality which is wrong.
You seem rattled. Do you really expect people to believe that the
wheel in your story could carry that much wounded pride around?
Simon Brooke
I posted a message to this thread (about hubs standing on spokes) late
last night which was uncalled for and which I'd like to apologise for
(particularly to Jobst). I'm posting this apology now before I read
anything else in the thread and get self-righteous or pissed off
again.
Memo to self: never post to Usenet at 2 in the morning.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
cal
jim beam
<snip>
> Since these cables bend around pulleys and curves, they must be
> helically wound or they would break immediately. They are made this
> way for the same reason control cables on bicycles are helically
> wound...
they're helically wound, but in the opposite direction to normal so that
the exterior strandlets run close to perpendicular. but you'd know that
if you'd actually seen the cable up close.
> so they will have uniform stress in all strands when bending
> around curves. Cable car cable has a special layer of external
> friction strands that are smooth and rectangular
absolutely incorrect. that might be a bad description of a die drawn
bike cable, but it's as far from cable car rope as it's possible to be.
that's why i said it was an interesting article worth seeing - it's
completely /atypical/! you've evidently never seen it up close.
jim beam
> That's a nice story but I think you are reconstructing the event from
> imagination. Wheels cannot slowly sink to a lower rolling diameter.
> The failure mode is lateral collapse and that jams the wheel in the
> frame so it won't turn. It makes a nice story but it didn't happen.
get a grip of yourself man. i know the difference between lateral
collapse and radial failure. and what i described was a serial
progressive radial failure. try and separate blind prejudice from
rational analysis.
Tim McNamara
> H'mmm...
>
> I posted a message to this thread (about hubs standing on spokes)
> late last night which was uncalled for and which I'd like to
> apologise for (particularly to Jobst). I'm posting this apology now
> before I read anything else in the thread and get self-righteous or
> pissed off again.
You might be able to cancel the post. Your newsreader might be able
to issue the appropriate command (another reason why one should use a
proper newsreader).
> Memo to self: never post to Usenet at 2 in the morning.
A good idea for many.
Werehatrack
<tim...@bitstream.net> may have said:
>You might be able to cancel the post. Your newsreader might be able
>to issue the appropriate command (another reason why one should use a
>proper newsreader).
Many servers do not honor cancels anymore due to the malicious cancel
floods that have been seen on numerous groups over the years. Issuing
a cancel is still a good idea, though, but it should be remembered
that a cancel won't necessarily take the post off of every server that
the original article may have reached.
--
My email address is antispammed; pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.
Words processed in a facility that contains nuts.
frkrygow
> jobst....@stanfordalumni.org wrote:
>
>>Pete Biggs writes:
>>
>>>You're likely to get broken spokes through metal fatigue if you
>>>continue with them slack.
>>
>>I read this admonition now and then and have not heard an explanation
>>of how slack spokes cause fatigue failures.
>
>
> I thought fatigue was caused by spokes repeatedly going from slack to taut
> and that the slacker the spokes, the more difference in tension there
> would be in use.
That's what I think, too. The same effect occurs in bolted joints
subjected to varying loads, which is why preload on bolts is important.
With sufficient preload, the variation in bolt tension is much less
than the variation in applied load. Average bolt tension is higher, but
the variable component is a much bigger contributor to failure. Either
Goodman's or Soderberg's failure criterion show this.
Spotts' text _Design of Machine Elements_ has a good treatment of this
for bolted joints. I've always assumed the exact same logic applied for
pretensioned spokes. In fact, Spotts points out the benefit of reducing
the shank diameter of a "tension bolt," which makes it look just like a
butted spoke!
--
Frank Krygowski [To reply, omit what's between "at" and "cc"]
Carl Fogel
Dear Jobst and Jim,
Assuming that Jim's mother's wheels were indeed as strong
as her thills, as Holmes assures us was good practice in
that era, perhaps the crucial defect actually lay in her
whippletree?
http://cs.wwc.edu/~aabyan/Poetry/holmes.html
The interesting failure mode of the shay invites
analysis.
Carl Fogel
Phil Holman
"Pete Biggs" <ptangerine{remove_fruit}@biggs.tc> wrote in message
news:bt8l6h$4er0j$1...@ID-144931.news.uni-berlin.de...
> jobst....@stanfordalumni.org wrote:
> > Pete Biggs writes:
> >> You're likely to get broken spokes through metal fatigue if you
> >> continue with them slack.
> >
> > I read this admonition now and then and have not heard an
explanation
> > of how slack spokes cause fatigue failures.
>
> I thought fatigue was caused by spokes repeatedly going from slack to
taut
> and that the slacker the spokes, the more difference in tension there
> would be in use.
The correctly tensioned wheel at any point in time has a couple of
spokes with a large stress reduction compared to the slack wheel which
has a large number of spokes with a small stress increase.
Phil Holman
Carl Fogel
> On Sun, 04 Jan 2004 11:18:19 -0600, Tim McNamara
> <tim...@bitstream.net> may have said:
>
> >You might be able to cancel the post. Your newsreader might be able
> >to issue the appropriate command (another reason why one should use a
> >proper newsreader).
>
> Many servers do not honor cancels anymore due to the malicious cancel
> floods that have been seen on numerous groups over the years. Issuing
> a cancel is still a good idea, though, but it should be remembered
> that a cancel won't necessarily take the post off of every server that
> the original article may have reached.
Dear Tim and Werehatrack,
While cancelling an ill-natured post might be
a step in the right direction, a silent erasure
is no match for a public apology--no one ever
compliments you on the character shown by a cancel.
There's more to life than technology (or so I hear).
Nice post, Simon.
Carl Fogel
jobst....@stanfordalumni.org
>>> You're likely to get broken spokes through metal fatigue if you
>>> continue with them slack.
>> I read this admonition now and then and have not heard an
>> explanation of how slack spokes cause fatigue failures.
> I thought fatigue was caused by spokes repeatedly going from slack
> to taut and that the slacker the spokes, the more difference in
> tension there would be in use.
It is the span of the stress change that causes fatigue. In some
materials and in some shapes that stress reversal (tension to
compression and back) accelerates fatigue failure but that is not the
vase with spokes. Rattlingly loose spokes have lesser stress changes
than taught ones and do not have reversed stress.
> "A spoked wheel relies on having all of the spokes in constant
> tension. A highly dished rear wheel starts with very light tension
> on the left side spokes. The torque of hard pedaling can cause the
> left side "leading" spokes to occasionally go completely slack
> momentarily. Repeated cycles of tension and slackness cause these
> spokes to fatigue at the bends, and ultimately break."
> - www.sheldonbrown.com/wheelbuild.html
That still does not show any effect that causes more rapid fatigue.
Besides, this is inaccurate. Left side spokes sometimes appear to
verify that model, but it is the greater bend at the elbow that causes
these failures, mainly because the wheel builder failed to improve the
spoke line after initial tensioning. That is, the outbound spokes
need to be pressed down manually against the flange so that they are
not free to flex repeatedly with each wheel rotation. Lower tension
on the left side does not accelerate fatigue. This notion needs to be
stamped out before it gets any more support. Meanwhile left side
spokes need more support.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> That's a nice story but I think you are reconstructing the event
>> from imagination. Wheels cannot slowly sink to a lower rolling
>> diameter. The failure mode is lateral collapse and that jams the
>> wheel in the frame so it won't turn. It makes a nice story but it
>> didn't happen.
> Get a grip of yourself man. I know the difference between lateral
> collapse and radial failure. And what i described was a serial
> progressive radial failure. Try and separate blind prejudice from
> rational analysis.
Please explain how the wheel, or better the axle of the wheel sank
closer and closer to the ground in your event of "radial wheel
collapse". Did the rim become oval and how did that rotate? What
were the spokes doing at that time? Maybe you can describe this so I
can correct what I have observed in wheel failures.
Jobst Brandt
jobst....@stanfordalumni.org
jim beam
closer & closer to the rim. rim was still relatively ok.