Spoke tension and stiffness?
Mike Lackey
I recently compared spoke tension on my wheels with a set of Wheelsmith
manufactured wheels. I discovered that the Wheelsmith wheels had a
higher tension. I then tweaked the spokes on my wheels to increase
tension a bit, knowing that increased tension would generally produce a
stronger wheel. I had not trued the wheels prior to this (approx 2000
miles) so I asusme that initial tension was OK for my weight and style
of riding.
Since I've increased the spoke tension, I have the perception that
there's a little less flex in the bottom bracket area of my bike.
First, I get on the bike, not moving, left foot on ground, right foot
clipped in, as if at a stop sign. Then I grab the brakes real hard and
squeeze. Then, I press real hard on the right pedal, or even try to
bounce it. It seems that the bottom bracket area has lex flex since
I've increased spoke tension.
I know that fork, tire pressure, probably dewpoint for that matter, all
have an effect on preceived stiffness of the bike. My question is,
could tweaking the spokes make a significant and noticeable difference,
or is it just a perception thing?
Reagrds,
Mike Lackey
Madsion, AL
Mark Atanovich
Mike Lackey <mla...@nospam.pesa.com> writes:
I know that fork, tire pressure, probably dewpoint for that matter,
all
> have an effect on preceived stiffness of the bike. My question is,
> could tweaking the spokes make a significant and noticeable difference,
> or is it just a perception thing?
Assuming spokes don't go slack, there is no effect on stiffness.
Mark Atanovich
"Good judgement comes from experience. Experience comes from bad
judgement."
Rinard
spoke tension.
See http://damonrinard.com/wheel/tension.gif
The wheel has essentially the same lateral deflection until the spokes
are so loose they become slack.
Mike Lackey wrote:
>
> This will probably open a can of worms, but here goes...
>
> I recently compared spoke tension on my wheels with a set of Wheelsmith
> manufactured wheels. I discovered that the Wheelsmith wheels had a
> higher tension. I then tweaked the spokes on my wheels to increase
> tension a bit, knowing that increased tension would generally produce a
> stronger wheel. I had not trued the wheels prior to this (approx 2000
> miles) so I asusme that initial tension was OK for my weight and style
> of riding.
>
> Since I've increased the spoke tension, I have the perception that
> there's a little less flex in the bottom bracket area of my bike.
> First, I get on the bike, not moving, left foot on ground, right foot
> clipped in, as if at a stop sign. Then I grab the brakes real hard and
> squeeze. Then, I press real hard on the right pedal, or even try to
> bounce it. It seems that the bottom bracket area has lex flex since
> I've increased spoke tension.
>
> I know that fork, tire pressure, probably dewpoint for that matter, all
> have an effect on preceived stiffness of the bike. My question is,
> could tweaking the spokes make a significant and noticeable difference,
> or is it just a perception thing?
>
> Reagrds,
> Mike Lackey
> Madsion, AL
--
Damon Rinard
Damon Rinard's Bicycle Tech Site:
http://www.damonrinard.com/
David T. Blake
Mike Lackey <mla...@nospam.pesa.com> wrote:
> I know that fork, tire pressure, probably dewpoint for that
> matter, all have an effect on preceived stiffness of the bike. My
> question is, could tweaking the spokes make a significant and
> noticeable difference, or is it just a perception thing?
If spokes are not going slack or plastic, spoke tension is
not related to stiffness.
--
Dave Blake
dbl...@phy.ucsf.edu
Qui si parla Campagnolo
could tweaking the spokes make a significant and noticeable difference,
or is it just a perception thing? >>
It CAN make a difference that you can feel-
peter
Mike Jacoubowsky
--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com
Qui si parla Campagnolo <vecc...@aol.com> wrote in message
news:19991105084824...@ng-ck1.aol.com...
Jeff
the spokes make the prestressed rim even stiffer? I believe that, that is
what prestressing is supposed to do.
I note Jobst found only 0.05mm lateral movement with a 160N lateral load on
what looks like a high flanged 36 spoked front wheel. I think that this is
about the same magnitude as that often used for truing (at least I'm happy
with +/- 0.05mm).
With a 16 spoked, 9 speed, rear wheel, defections may be considerably
greater. Jobst shows a 6 speed rear wheel (probably 36 spokes) may become
unloaded (left side spokes) if it is laterally deflected to the left by
about 3 mm due to a lateral force of around 200N (see page 39 of the 3rd
edition). I can only infer from this that lateral deflections are quite
small unless spoke tension is raised, such as when used with lower spoke
count wheels, otherwise the wheels would be continually failing.
In any case even if the lateral deflections are noticeable then its is still
a question of whether increased rim stiffness would make a noticeable
difference. Perhaps a stiffer rim could bring more spokes into play.
Someone could measure defections with higher and lower spoke tension, in a
fashion similar to that which Jobst used, when he compared the effects of
tying and soldering on stiffness.
Regards
Jeff
Mark Atanovich <Atan...@prodigy.net> wrote in message
news:7vsj8i$du8$1...@newsgate.sps.mot.com...
[snip]
> Assuming spokes don't go slack, there is no effect on stiffness.
[snip]
Jobst Brandt
> Agreed about the spokes on their own. However, would not extra
> tension on the spokes make the prestressed rim even stiffer? I
> believe that, that is what prestressing is supposed to do.
Metals do not change their elastic properties with preload. I'm not
sure what you mean by prestressing because most people who confuse
elasticity with stiffness also confuse stress relieving with
prestressing. What you believe you read in "the Bicycle Wheel" is
not correct. Lateral deflections were greater than what you mention.
> In any case even if the lateral deflections are noticeable then its
> is still a question of whether increased rim stiffness would make a
> noticeable difference. Perhaps a stiffer rim could bring more spokes
> into play.
That's often the case but there is a practical limit and it isn't
linear since bending curves are third power curves with respect to
load.
> Someone could measure defections with higher and lower spoke
> tension, in a fashion similar to that which Jobst used, when he
> compared the effects of tying and soldering on stiffness.
This is unnecessary because load independence of steel is well
understood.
Jobst Brandt <jbr...@hpl.hp.com>
Brian Nystrom
Qui si parla Campagnolo wrote:
> << My question is,
> could tweaking the spokes make a significant and noticeable difference,
> or is it just a perception thing? >>
>
> It CAN make a difference that you can feel-
> peter
I disagree. I've had wheels with spoke tensions low enough that you could
HEAR the spokes moving when climbing and rocking the bike side to side.
After re-tensioning them, the noise was gone, but they felt the same. The
wheels still flexed, but the spokes didn't lose tension enough to move and
make noise.
--
Regards
Brian
Jobst Brandt
>> My question is, could tweaking the spokes make a significant and
>> noticeable difference, or is it just a perception thing? >>
> It CAN make a difference that you can feel-
Can you explain what could cause that difference?
Jobst Brandt <jbr...@hpl.hp.com>
David T. Blake
> Agreed about the spokes on their own. However, would not extra
> tension on the spokes make the prestressed rim even stiffer? I
> believe that, that is what prestressing is supposed to do.
The load on the rim would be higher.
But the rim is still loaded in its elastic range, and
will show the same change in shape for a given change in load.
> With a 16 spoked, 9 speed, rear wheel, defections may be
> considerably greater. Jobst shows a 6 speed rear wheel (probably
> 36 spokes) may become unloaded (left side spokes) if it is
> laterally deflected to the left by about 3 mm due to a lateral
> force of around 200N (see page 39 of the 3rd edition). I can only
> infer from this that lateral deflections are quite small unless
> spoke tension is raised, such as when used with lower spoke count
> wheels, otherwise the wheels would be continually failing.
Right.
Another way to think of this is that rather insubstantial lateral
loads will cause you to fall pretty quickly. That you can balance
indicates that most lateral loads are small.
> In any case even if the lateral deflections are noticeable then
> its is still a question of whether increased rim stiffness would
> make a noticeable difference. Perhaps a stiffer rim could bring
> more spokes into play.
It would, but you'd need a rim with stiffer material properties,
not a rim with higher total radial compression.
> Someone could measure defections with higher and lower spoke
> tension, in a fashion similar to that which Jobst used, when he
> compared the effects of tying and soldering on stiffness.
Such results have been posted here before in misguided attempts
to claim that spoke tension has no effect on wheel strength -
misguided because stiffness and strength are not strictly related.
--
Dave Blake
dbl...@phy.ucsf.edu
John Everett
built wheels don't handle lateral loads very well. One of my training partners
has a computer pickup that requires positioning VERY close to the magnet (like
about 1mm). Whenever she hits her front brake (which obviously isn't centered
properly) the magnet hits the pickup with an accompanying thudding noise. I've
been considering increasing the spoke tension, although the spokes seem to be
"about right" now. From what I've been gathering on this thread I'm guessing
I'd have better results centering her brake.
--
jeverett<AT>wwa<DOT>com (John Everett) http://www.wwa.com/~jeverett
Joe Rutledge
--
Regards,
Joe Rutledge
Jobst Brandt wrote in message <8025gs$lud$3...@hplms2.hpl.hp.com>...
Jeff
problem, just being in too much of a hurry to find a reference.)
1) When you say on page 123 of the third edition that "Lateral deflections
caused by a 160N vertical force applied repeatedly at four different
locations remain unchanged within 0.05 mm before and after tying the
spokes." You clearly meant that the difference in deflections between tying
and not tying are not greater than 0.05mm. You did not mean or imply that
lateral deflections were only 0.05mm or less. Sorry for talking about your
book and getting it wrong and thanks for picking me up on this.
I have assumed here that it is 0.05mm figure and not the 3mm figure for rear
wheels that you were questioning.
2) I did the following experiment. I took a 300mm steel ruler and placed it
between the faces of a G style clamp. I placed enough end load on the ruler
(using the clamp) to get the ruler to bend slightly downwards by about 5mm
in the center. A dial guage (0.01mm graduation) was placed over the ruler so
that it measured verticle deflections at the ruler's center. I placed a
small 200 gram object (2 newtons) as close as possible to the middle of the
ruler. I recorded a deflection of 0.8mm. Then I placed more end load on the
ruler by tightening the clamp. It bent a little more to about 10mm total
deflection and I repeated the loading with the same object and measured a
new deflection of only 0.3mm this time round. So placing the steel ruler
under additional compression seems to have reduce the deflection by more
than 50%.
I'm not sure how much of the observed effect is due to extra bending and how
much is due to extra prestressing but there does seem to be a real
difference. I don't really have any knowledge of what is happening here and
just trying to use my common sense (or is it, lack of it). The deflection
test load I used was a 27mm steel socket.
Regards
Jeff
(smith....@hunterlink.net.au)
Jeff
curves during the routine testing of steel wire. These often do not show a
particularly linear region close to zero tension due to things like forces
required to
straighten the sample. Often computer software or human operators back
extrapolate that portion of the stress strain curve with a straight line.
Other problems with measuring equipment can also effect this region.
Anyway here is my thinking. If the spokes bend where they cross over each
other (cross pattern lacing), then this may effect the linearity of the
stress strain curve. Certainly operators of tensile testing equipment have
told me that bent samples produce curves (rather then straight lines) at the
lower end of the stress strain curves.
Regards
Jeff
Jeff
aluminium extrusion. It looks like a straight beam and has dimensions of
11mm by 18 mm. It is hollow and has a wall thickness of about 0.6mm. This
is more typical of a rim cross section then the steel ruler (below) was. The
extrusion produces no observable curvature due to any of the compressive
forces I applied.
This time I used a threaded steel rod to compress the beam. I packed the
threaded rod at both ends to ensure that it was clear of the internals of
the beam. I used a greater mass of 1kg (10 newtons) to get a measurable
deflection (of 0.15mm).
When compressive force was zero, adding a 1kg mass to the centre of the beam
caused a deflection of 0.15mm. When I added some compression the beam, the
1kg mass displaced the centre by 0.15mm. When I added a lot more compression
the beam, the 1kgs mass displaced its centre by 0.15mm. I guess I am now
satisfied that deflections in a bicycle wheel rim are not affected by the
prestress and therefore rim stiffness is not effected by any changes in
spoke tension. I don't understand the engineering or science involved here
but seeing is believing in my case.
I can only assume the differences observed when using the steel rule were
due to its bending action and not due to a difference in prestress levels.
Regards
Jeff
BTW is was very impressive just how strong this light weight (about
100grams) Al extrusion was. Even with a one meter length, it takes a lot to
bend it.
Jeff <smith....@hunterlink.net.au> wrote in message
news:3824...@news.hunterlink.net.au...
[snip]
> 2) I did the following experiment. I took a 300mm steel ruler and placed
it
> between the faces of a G style clamp. I placed enough end load on the
ruler
> (using the clamp) to get the ruler to bend slightly downwards by about 5mm
> in the center. A dial guage (0.01mm graduation) was placed over the ruler
so
> that it measured verticle deflections at the ruler's center. I placed a
> small 200 gram object (2 newtons) as close as possible to the middle of
the
> ruler. I recorded a deflection of 0.8mm. Then I placed more end load on
the
> ruler by tightening the clamp. It bent a little more to about 10mm total
> deflection and I repeated the loading with the same object and measured a
> new deflection of only 0.3mm this time round. So placing the steel ruler
> under additional compression seems to have reduce the deflection by more
> than 50%.
>
> I'm not sure how much of the observed effect is due to extra bending and
how
> much is due to extra prestressing but there does seem to be a real
> difference. I don't really have any knowledge of what is happening here
and
> just trying to use my common sense (or is it, lack of it). The deflection
> test load I used was a 27mm steel socket.
>
[snip]
Mike Jacoubowsky
you would feel the difference. This is obviously extreme and not likely
relevant. But as spoke tensions increase on the side opposite the gears,
aren't you bringing in more "pulling" spokes while applying power? I
suppose the flip side of this would be that increased tension on the side
opposite the gears implies even greater tension on the gear side, such that
nearly all work is still done by the gear-side spokes, but I'm not sure this
is the case.
The question involves "windup" of the rear wheel and whether spoke tension
makes any difference whatsoever. We're not talking about side-to-side
forces while cornering.
--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com
Jobst Brandt <jbr...@hpl.hp.com> wrote in message
news:8025gs$lud$3...@hplms2.hpl.hp.com...
Mark Hickey
>Agreed.
>
>--Mike-- Chain Reaction Bicycles
>http://www.ChainReactionBicycles.com
>
>Qui si parla Campagnolo <vecc...@aol.com> wrote in message
>news:19991105084824...@ng-ck1.aol.com...
><< My question is,
>could tweaking the spokes make a significant and noticeable difference,
>or is it just a perception thing? >>
>
>It CAN make a difference that you can feel-
>peter
Uh oh...
Let's think about this one for a minute. I respect Peter and Mike,
but also Jobst, Damon and the teeming masses that claim that spoke
tension cannot possibly alter the "feel" of a wheel.
Given the fact that spokes are under such an enormous stress, and that
they cannot possibly "stretch" to absorb a bump, it seems that there
should be no doubt that a properly built spoked wheel will transfer
all bumps to the hub in an identical manner.
BUT, could it be that once again it's a matter of "high frequency, low
amplitude road buzz" coming into play? Think about a "tin can
telephone" (two tin cans with a string pulled taut between the two
"bottoms"). The tighter you pull, the better the sound is
transmitted. The spoke is the "string" in this model, and certainly
is capable of resonating at "road buzz" frequencies. This resonance
can be altered by changing the spoke tension.
To take the same analogy further, a BUMP would be like giving a hearty
pull on one of the tin cans. Wouldn't matter much if the string was
at 80% or 100% "optimal" tension. That is, you can't "absorb bumps"
by loosening spokes.
Dang, where did we put that function generator and those transducers?
Mark Hickey
Habanero Cycles
http://www.cynetfl.com/habanero/
Home of the $695 ti frame
David T. Blake
> BUT, could it be that once again it's a matter of "high
> frequency, low amplitude road buzz" coming into play? Think about
> a "tin can telephone" (two tin cans with a string pulled taut
> between the two "bottoms").
So, let's postulate the wheel as a frequency filter of sorts.
The issue I take with that is that the rubber in the tire acts
as a tremendous low pass filter, and has compliance orders of
magnitude greater than the wheel. This is where the princess and
the pea defense comes up. Pretend I am from Missouri and show me.
--
Dave Blake
dbl...@phy.ucsf.edu
David T. Blake
> How far does it need to be taken? Clearly, if spokes were
> flopping around, you would feel the difference. This is obviously
> extreme and not likely relevant. But as spoke tensions increase
> on the side opposite the gears, aren't you bringing in more
> "pulling" spokes while applying power?
If all metal components are always in the linear phases of their
stress strain curves, there is effect of preload on strain for
any applied load.
--
Dave Blake
dbl...@phy.ucsf.edu
Mark McMaster
> The question involves "windup" of the rear wheel and whether spoke tension
> makes any difference whatsoever.
If by "windup" of the rear wheel you mean rotation of the
hub with respect to the rim, don't worry about it. Metal
spoked wheels have essentially no windup (regardless of
spoke tension). There is more drivetrain windup in the
compression of the socks in your shoes than in any metal
spoked wheel.
Mark McMaster
MMc...@ix.netcom.com
Mark Hickey
Awww, Dave... I don't even have time to do decent rides lately... how
the heck am I gonna do this? ;-)
I agree with you that the rubber tires will act like a pretty
effective attenuator to audio frequencies, but there is a LOT of input
to them, so even a very small amount of that accoustic energy getting
through them could be significant.
Again, we're talking about audio frequencies, so it's not really
anything you're going to "feel", but there would still be some
potenital fatigue effects. Errrr, to the rider, not the bike.
Drop a high pressure wheel, bouncing it off a hard surface, and you'll
hear it "sing". That's significant because even though the "input"
was only one pulse, it excited the wheel to produce a high-pitched
"ringing". I have to believe rolling over hundreds of "bumps" per
second (asphalt) would be more likely to do the same thing, since the
input to the wheel would contain a higher percentage of the resonant
frequency (actually, frequencIES) of the wheel, even if the total
energy was less.
Anyone want to try this at home? Anyone with some exotic equipment,
that is.....
Joe Rutledge
next time he tells me that he can REALLY feel the difference. I've been
telling him it's tire pressure. Now, when I tell him it's his socks, I can't
wait to hear the reply!
--
Regards,
Joe Rutledge
Mark McMaster wrote in message <382621C6...@ix.netcom.com>...
<<snipped>>
>...There is more drivetrain windup in the
Jobst Brandt
> Since I've increased the spoke tension, I have the perception that
> there's a little less flex in the bottom bracket area of my bike.
> First, I get on the bike, not moving, left foot on ground, right
> foot clipped in, as if at a stop sign. Then I grab the brakes real
> hard and squeeze. Then, I press real hard on the right pedal, or
> even try to bounce it. It seems that the bottom bracket area has
> lex flex since I've increased spoke tension.
Much better controlled measurements have been made and currently a
series of such measurements are being conducted by Damon Rainard who
will add this to his web site when completed.
As has been mentioned by others, steel does not change its elastic
properties with tension or compression within its elastic range (the
range where is does not permanently stretch). If you can feel a
difference, it must be that your wheel was so loose that the off-side
spokes were going slack. This is more easily the case with rear
wheels whose left side has low tension. Rear wheels are
asymmetrically strong, collapsing to the left far more easily than to
the right. This is described graphically in "the Bicycle Wheel".
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> Given the fact that spokes are under such an enormous stress, and
> that they cannot possibly "stretch" to absorb a bump, it seems that
> there should be no doubt that a properly built spoked wheel will
> transfer all bumps to the hub in an identical manner.
Spokes are not under "enormous stress" and they do not absorb bumps by
stretching. This perception is what causes all these incorrect
assessments of what is going on. The wheel carries loads by unloading
spokes, specifically four to five spokes in the tire contact zone at
the ground. That impacts are transmitted to the hub, however, is
correct and it is by way of steel that experiences minute length
change for even the harshest bump.
> BUT, could it be that once again it's a matter of "high frequency,
> low amplitude road buzz" coming into play? Think about a "tin can
> telephone" (two tin cans with a string pulled taut between the two
> "bottoms"). The tighter you pull, the better the sound is
> transmitted. The spoke is the "string" in this model, and certainly
> is capable of resonating at "road buzz" frequencies. This resonance
> can be altered by changing the spoke tension.
The damping of the string is a variable fuzz ball that becomes more
solid when tensioned. Your example is a poor parallel to a spoke
whose density and elasticity does not change with stress. Your
analogies are not applicable because the change in resonance of a
spoke with tension is a lateral vibration as in a stringed instrument
but we are not hearing any tones from the spokes.
> To take the same analogy further, a BUMP would be like giving a
> hearty pull on one of the tin cans. Wouldn't matter much if the
> string was at 80% or 100% "optimal" tension. That is, you can't
> "absorb bumps" by loosening spokes.
That what you say but it wrong! I think you need to review the matter
of "how the wheel supports loads". There is a book that is often
discussed in this NG.
Jobst Brandt <jbr...@hpl.hp.com>
Mark Hickey
>Mark Hickey writes:
>
>> Given the fact that spokes are under such an enormous stress, and
>> that they cannot possibly "stretch" to absorb a bump, it seems that
>> there should be no doubt that a properly built spoked wheel will
>> transfer all bumps to the hub in an identical manner.
>
>Spokes are not under "enormous stress" and they do not absorb bumps by
>stretching. This perception is what causes all these incorrect
>assessments of what is going on. The wheel carries loads by unloading
>spokes, specifically four to five spokes in the tire contact zone at
>the ground. That impacts are transmitted to the hub, however, is
>correct and it is by way of steel that experiences minute length
>change for even the harshest bump.
Jobst, we're in violent agreement here, other than in the definition
of "enormous". To me, stressing a steel wire to the point of
resonance at a high C is "enormous tension".
>> BUT, could it be that once again it's a matter of "high frequency,
>> low amplitude road buzz" coming into play? Think about a "tin can
>> telephone" (two tin cans with a string pulled taut between the two
>> "bottoms"). The tighter you pull, the better the sound is
>> transmitted. The spoke is the "string" in this model, and certainly
>> is capable of resonating at "road buzz" frequencies. This resonance
>> can be altered by changing the spoke tension.
>
>The damping of the string is a variable fuzz ball that becomes more
>solid when tensioned. Your example is a poor parallel to a spoke
>whose density and elasticity does not change with stress. Your
>analogies are not applicable because the change in resonance of a
>spoke with tension is a lateral vibration as in a stringed instrument
>but we are not hearing any tones from the spokes.
I was refering to the resonance - which does change with tension. But
part of the mechanism is mechanical, with the more tension between the
two surfaces (string and can, spoke nipple and rim) potentially adding
to the efficiency of transfer of small amplitude, high-frequency
vibrations from one to the other. I know that a highly-tensioned
wheel makes a LOT more noise than a low-tension cruiser wheel when you
"strum the spokes". That indicates it could potentially send more
audio-frequency impulses to the rider through the fork.
>> To take the same analogy further, a BUMP would be like giving a
>> hearty pull on one of the tin cans. Wouldn't matter much if the
>> string was at 80% or 100% "optimal" tension. That is, you can't
>> "absorb bumps" by loosening spokes.
>
>That what you say but it wrong! I think you need to review the matter
>of "how the wheel supports loads". There is a book that is often
>discussed in this NG.
>
>Jobst Brandt <jbr...@hpl.hp.com>
I think the analogy is appropriate, and clearly explains the "orders
of magnitude" difference in the two effects that were being discussed.
I know that the "pull" is actually more of a "push" and is relative to
the tension on the bottom spokes - but with bicycle wheels, no analogy
is 100% applicable.
Jobst Brandt
>>> Given the fact that spokes are under such an enormous stress, and
>>> that they cannot possibly "stretch" to absorb a bump, it seems that
>>> there should be no doubt that a properly built spoked wheel will
>>> transfer all bumps to the hub in an identical manner.
>> Spokes are not under "enormous stress" and they do not absorb bumps by
>> stretching. This perception is what causes all these incorrect
>> assessments of what is going on. The wheel carries loads by unloading
>> spokes, specifically four to five spokes in the tire contact zone at
>> the ground. That impacts are transmitted to the hub, however, is
>> correct and it is by way of steel that experiences minute length
>> change for even the harshest bump.
> Jobst, we're in violent agreement here, other than in the definition
> of "enormous". To me, stressing a steel wire to the point of
> resonance at a high C is "enormous tension".
That is still far below the elastic limit and in terms of steel wire,
that ain't nuthin. Although it may be tight with respect to a kite
string.
>>> BUT, could it be that once again it's a matter of "high frequency,
>>> low amplitude road buzz" coming into play? Think about a "tin can
>>> telephone" (two tin cans with a string pulled taut between the two
>>> "bottoms"). The tighter you pull, the better the sound is
>>> transmitted. The spoke is the "string" in this model, and certainly
>>> is capable of resonating at "road buzz" frequencies. This resonance
>>> can be altered by changing the spoke tension.
>> The damping of the string is a variable fuzz ball that becomes more
>> solid when tensioned. Your example is a poor parallel to a spoke
>> whose density and elasticity does not change with stress. Your
>> analogies are not applicable because the change in resonance of a
>> spoke with tension is a lateral vibration as in a stringed instrument
>> but we are not hearing any tones from the spokes.
> I was refering to the resonance - which does change with tension.
I just said that but we are not talking about lateral vibrations in
the acoustic range. In fact there are none or we would be constantly
musically entertained while riding.
> But part of the mechanism is mechanical, with the more tension
> between the two surfaces (string and can, spoke nipple and rim)
> potentially adding to the efficiency of transfer of small amplitude,
> high-frequency vibrations from one to the other.
The can acts as a drum skin. There is no parallel in a bicycle wheel.
the rim does not vibrate as a drum skin.
> I know that a highly-tensioned wheel makes a LOT more noise than a
> low-tension cruiser wheel when you "strum the spokes". That
> indicates it could potentially send more audio-frequency impulses to
> the rider through the fork.
That implies that you can detect acoustic differences in the spokes of
a wheel due to tension. I think you are confusing that with tire
resonance when highly inflated. That is something that can be heard
and it is related to drum skin resonance.
>>> To take the same analogy further, a BUMP would be like giving a
>>> hearty pull on one of the tin cans. Wouldn't matter much if the
>>> string was at 80% or 100% "optimal" tension. That is, you can't
>>> "absorb bumps" by loosening spokes.
>> That what you say but it wrong! I think you need to review the matter
>> of "how the wheel supports loads". There is a book that is often
>> discussed in this NG.
> I think the analogy is appropriate, and clearly explains the "orders
> of magnitude" difference in the two effects that were being discussed.
> I know that the "pull" is actually more of a "push" and is relative to
> the tension on the bottom spokes - but with bicycle wheels, no analogy
> is 100% applicable.
In that case, there are apparently no limits what one can drag into
the discussion by its coat tails. On that basis anything goes.
Jobst Brandt <jbr...@hpl.hp.com>
Nick Maclaren
In article <807s7q$2qr$1...@hplms2.hpl.hp.com>, jbr...@hpl.hp.com (Jobst Brandt) writes:
|>
|> Mark Hickey writes:
|>
|> > Jobst, we're in violent agreement here, other than in the definition
|> > of "enormous". To me, stressing a steel wire to the point of
|> > resonance at a high C is "enormous tension".
|>
|> That is still far below the elastic limit and in terms of steel wire,
|> that ain't nuthin. Although it may be tight with respect to a kite
|> string.
It depends on your kite - I have seen one flowing using piano wire
on a winch, which was humming merrily in the wind :-)
More seriously, the spoke AS A CONSTRUCTION is near its elastic
limit, if only in the region around the elbow. The wire of the
spoke isn't, but that isn't what fails. In a well-built wheel
with a good hub and spokes, even the elbow may be safely below
the elastic limit, but an unfair stress (e.g. one caused by
moving the wheel while locked) can easily put it above that.
Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QG, England.
Email: nm...@cam.ac.uk
Tel.: +44 1223 334761 Fax: +44 1223 334679
Martin Jervis
It's true that a spoke's stiffness in tension is the same whatever the
stress
in it, providing the stress is within the elastic range. However, in
compresssion
it will have zero stiffness, either due to buckling or the nipple end being
unsupported. If the wheel is lightly tensioned then under load the stress in
the spokes
on the compression side of the wheel (ie the bottom portion) may actually
drop to zero
and thus their contribution to the stiffness of the wheel will be lost. If
the
prestress is higher then the spokes will remain in tension (albeit at a
lower stress)
even when the wheel is loaded and thus the wheel will be stiffer as a
greater number
of spokes are now effective. This is a purely theoretical argument -I have
no data
on typical spoke loads to back this up. Has anyone else?
Jerv
David T. Blake
> Just like to add my thoughts to this interesting discussion.
>
> It's true that a spoke's stiffness in tension is the same
> whatever the stress in it, providing the stress is within the
> elastic range. However, in compresssion it will have zero
> stiffness, either due to buckling or the nipple end being
> unsupported. If the wheel is lightly tensioned then under load
> the stress in the spokes on the compression side of the wheel (ie
> the bottom portion) may actually drop to zero and thus their
> contribution to the stiffness of the wheel will be lost.
Purely theoretical is right.
How long do you think your wheel will stay in true if the spoke
tension cycles through zero ?? As though spokes wouldn't unscrew
quite fast. Further, even small increments above the zero tension
point will buckle the rim. If this operating point is even close to
what occurs in normal use, the wheel is toast.
--
Dave Blake
dbl...@phy.ucsf.edu
Brian Nystrom
Martin Jervis wrote:
> Just like to add my thoughts to this interesting discussion.
>
> It's true that a spoke's stiffness in tension is the same whatever the stress
> in it, providing the stress is within the elastic range. However, in
> compresssion
> it will have zero stiffness, either due to buckling or the nipple end being
> unsupported. If the wheel is lightly tensioned then under load the stress in
> the spokes
> on the compression side of the wheel (ie the bottom portion) may actually drop
> to zero
> and thus their contribution to the stiffness of the wheel will be lost. If the
>
> prestress is higher then the spokes will remain in tension (albeit at a lower
> stress)
> even when the wheel is loaded and thus the wheel will be stiffer as a greater
> number
> of spokes are now effective. This is a purely theoretical argument -I have no
> data
> on typical spoke loads to back this up. Has anyone else?
>
> Jerv
Your assumptions are correct. One of the key points to building durable wheels
is to get the spokes tight enough that they never lose tension completely in
normal use. If the spokes are allowed to reach zero tension frequently, they
will fatigue and fail in short order. The wheel will also be prone to collapse.
--
Regards
Brian
Rick Denney
>Just like to add my thoughts to this interesting discussion.
>
>It's true that a spoke's stiffness in tension is the same whatever the
>stress
>in it, providing the stress is within the elastic range. However, in
>compresssion
>it will have zero stiffness, either due to buckling or the nipple end being
>unsupported. If the wheel is lightly tensioned then under load the stress in
>the spokes
>on the compression side of the wheel (ie the bottom portion) may actually
>drop to zero
>and thus their contribution to the stiffness of the wheel will be lost. If
>the
> prestress is higher then the spokes will remain in tension (albeit at a
>lower stress)
>even when the wheel is loaded and thus the wheel will be stiffer as a
>greater number
>of spokes are now effective. This is a purely theoretical argument -I have
>no data
>on typical spoke loads to back this up. Has anyone else?
>
>Jerv
>
>
All this has been publlished in Brandt's _The Bicycle Wheel_ and
reiterated many times around here.
Of course, you would never want to design a wheel such that the spokes
go slack. Not only would it readily go out of true, but it would
collapse in the presence of the right bump.
You are correct that the stiffness and strength of the wheel is in the
spokes, and when they go slack (due to load exceeding prestress), the
wheel loses both.
Rick "Brandt did both finite-element analysis and physical testing"
Denney
Martin Jervis
David T. Blake <dbl...@popper.ucsf.edu> wrote in message
news:slrn843hor...@popper.ucsf.edu...
.
>
> Purely theoretical is right.
>
> How long do you think your wheel will stay in true if the spoke
> tension cycles through zero ?? As though spokes wouldn't unscrew
> quite fast. Further, even small increments above the zero tension
> point will buckle the rim. If this operating point is even close to
> what occurs in normal use, the wheel is toast.
>
> --
> Dave Blake
I would guess a typical spoke prestress to be somewhere in the range of 100
to 300 newtons per square mm.
To reduce this stress to zero would only require the rim deflecting towards
the hub by 0.3mm (for 200Newtons)assuming the spoke to be 300mm long. I
would think it quite likely that this could occur on a few of the most
highly loaded spokes around the tyre contact area, especially if they're
only stressed to 100N (0.15mm deflection). Further I would be surprised if
deflections of this magnitude caused the rim to buckle. I don't think this
is the same situation as a broken spoke on an unloaded wheel. The
surrounding spokes here are still under full tension and will pull the rim
sideways because of the imbalance of lateral forces.
I'm not in anyway recommending slack spoking, but how long the rim will stay
true would depend on the stiffness of the rim. Old steel rims could manage
quite well with a few slack spokes if my childhood memories are correct!
I hate to disagree again but I don't think the nipples would unscrew either.
The slots in the heads are usually embedded in the rim tape to some extent
and the time spent at zero stress would be very brief. Spokes slacken due to
creep eventually.
> dbl...@phy.ucsf.edu
David T. Blake
> David T. Blake <dbl...@popper.ucsf.edu> wrote in message
> news:slrn843hor...@popper.ucsf.edu...
> > Purely theoretical is right.
> >
> > How long do you think your wheel will stay in true if the
> > spoke tension cycles through zero ?? As though spokes wouldn't
> > unscrew quite fast. Further, even small increments above the zero
> > tension point will buckle the rim. If this operating point is
> > even close to what occurs in normal use, the wheel is toast.
> I would guess a typical spoke prestress to be somewhere in the
> range of 100 to 300 newtons per square mm. To reduce this stress
> to zero would only require the rim deflecting towards the hub by
> 0.3mm (for 200Newtons)assuming the spoke to be 300mm long. I
> would think it quite likely that this could occur on a few of the
> most highly loaded spokes around the tyre contact area,
> especially if they're only stressed to 100N (0.15mm deflection).
Rim deflections are measured as up to about 6 mil, with 40 microns/mil,
or up to 0.2 mm. And 6 mil is a large deflection. 3-4 is more the
operational range, at 120-160 microns.
> I hate to disagree again but I don't think the nipples would
> unscrew either. The slots in the heads are usually embedded in
> the rim tape to some extent and the time spent at zero stress
> would be very brief. Spokes slacken due to creep eventually.
METALS DO NOT CREEP.
METALS DO NOT CREEP.
Substantial reductions in spoke tension will cause nipples
to unscrew. Nipples unscrewing cause spokes to go slack.
--
Dave Blake
dbl...@phy.ucsf.edu