Jhas wrote:> After last week's lively and informative discussion re "Cabon Fiber> Seat Stays = Better Ride?" I feel compelled to ask: can the same be> said for S-bend seat and chain stays? Lots of manufacturers claim that> s-bend stays add "vertical compliance" or increase lateral stiffness.> I'm having a difficult time believing any of it.> the fact is that they do increase compliance. the degree to which it happens however depends on execution, material etc. for a demo of the principle, google for "euler buckling". bent stays are essentially pre-buckled. imo, bent seat stays are good, bent chain stays are bad.
I have two frames from the same manufacturer (Litespeed), made from the same material (titanium), one with s-bend seat and chain stays and one without. No discernible difference when shod with the same tyres pumped to the same pressure.
OTOH, s-bend on the chainstay does serve a function in giving better heel clearance because the stay initially comes in from the dropouts at a sharper angle. I ride toes out and had to grind off the inside of the heels on my Carnac touring shoes or they hit the chainstays just forward of the dropout on my steel touring bike that has straight chainstays.
Nick
"Jhas" <joshua.hassol@volpe.dot.gov> wrote in message news:1113828574.768185.27780@f14g2000cwb.googlegroups.com...> After last week's lively and informative discussion re "Cabon Fiber> Seat Stays = Better Ride?" I feel compelled to ask: can the same be> said for S-bend seat and chain stays? Lots of manufacturers claim that> s-bend stays add "vertical compliance" or increase lateral stiffness.> I'm having a difficult time believing any of it.>
David L. Johnson 18 April 2005 17:29:12 [ permanent link ]
On Mon, 18 Apr 2005 06:07:22 -0700, jim beam wrote:
Jhas wrote:>> After last week's lively and informative discussion re "Cabon Fiber>> Seat Stays = Better Ride?" I feel compelled to ask: can the same be>> said for S-bend seat and chain stays? Lots of manufacturers claim that>> s-bend stays add "vertical compliance" or increase lateral stiffness.>> I'm having a difficult time believing any of it.
As you should. >>
the fact is that they do increase compliance. the degree to which it > happens however depends on execution, material etc. for a demo of the > principle, google for "euler buckling". bent stays are essentially > pre-buckled. imo, bent seat stays are good, bent chain stays are bad.
That is certainly reassuring, to imagine that curved stays are "buckled". The advantages are what, exactly? I had an old fork that was locally euler buckled after a crash. Perhaps I should have kept that, but somehow I thought that would be a bad idea.
--
David L. Johnson
__o | Let's not escape into mathematics. Let's stay with reality. -- _`\(,_ | Michael Crichton (_)/ (_) |
David L. Johnson wrote:> On Mon, 18 Apr 2005 06:07:22 -0700, jim beam wrote:>
Jhas wrote:>>
After last week's lively and informative discussion re "Cabon Fiber>>>Seat Stays = Better Ride?" I feel compelled to ask: can the same be>>>said for S-bend seat and chain stays? Lots of manufacturers claim that>>>s-bend stays add "vertical compliance" or increase lateral stiffness.>>>I'm having a difficult time believing any of it.>
As you should. >
the fact is that they do increase compliance. the degree to which it >>happens however depends on execution, material etc. for a demo of the >>principle, google for "euler buckling". bent stays are essentially >>pre-buckled. imo, bent seat stays are good, bent chain stays are bad.>
That is certainly reassuring, to imagine that curved stays are "buckled". > The advantages are what, exactly? I had an old fork that was locally> euler buckled after a crash. Perhaps I should have kept that, but somehow> I thought that would be a bad idea.>
that's bent, as in bending beam, not compression buckled, per euler. but i guess engineering was not your point.
"Jhas" <joshua.hassol@volpe.dot.gov> wrote in message news:1113828574.768185.27780@f14g2000cwb.googlegroups.com...> After last week's lively and informative discussion re "Cabon Fiber> Seat Stays = Better Ride?" I feel compelled to ask: can the same be> said for S-bend seat and chain stays? Lots of manufacturers claim that> s-bend stays add "vertical compliance" or increase lateral stiffness.> I'm having a difficult time believing any of it.>
It's marketing b*llsh*t.
Some pedants will claim that there IS an added degree of compliance but if so it is vastly smaller than that produced by the tyres. Suspect anyone who insists on this of having a hidden agenda...
In article <1113829678.ff940e043a380ff9b29ac0028169990d@teranews>, jim beam says...
the fact is that they do increase compliance. the degree to which it >happens however depends on execution, material etc. for a demo of the >principle, google for "euler buckling". >
Physics, abstract physics/0501099 Euler buckling in red blood cells: An optically driven biological micromotor
Authors: A. Ghosh, S. Sinha, J. A. Dharmadhikari, S. Roy, A. K. Dharmadhikari, J. Samuel, S. Sharma, D. Mathur
We report the observation of an optically driven micromotor of biological origin. A single red blood cell (RBC) folds when placed in an optical trap. The folded RBC is birefringent and rotates in circularly polarized light. Optical forces permit a high degree of control over the speed and direction of rotation of such a micromotor. This cellular micromotor has potential applications in micromanipulation, possibly like an "optical screwdriver" to apply torques at the micron scale. A simple theoretical model captures the main observed features and makes predictions that are successfully tested.
Acutally what happens is that the bent seat stays cause Euler buckling of your red blood cells of your butt. This results in better oxygen delivery and hence less discomfort. The claim that it also improves you speed is however false.
On 18 Apr 2005 05:49:34 -0700, "Jhas" <joshua.hassol@volpe.dot.gov> wrote:
After last week's lively and informative discussion re "Cabon Fiber>Seat Stays = Better Ride?" I feel compelled to ask: can the same be>said for S-bend seat and chain stays? Lots of manufacturers claim that>s-bend stays add "vertical compliance" or increase lateral stiffness.>I'm having a difficult time believing any of it.
IMO, any frame "feature" that claims to use flexure to improve the ride is either snake oil or a misfeature. The main purpose of the frame is to be a *frame*, to provide the rigid structure that keeps all of the other components aligned. Any flexing that may occur is incidental and largely of value only to the marketing droids. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts.
On 18 Apr 2005 08:02:04 -0700, Ed <Ed_member@newsguy.com> wrote:
Acutally what happens is that the bent seat stays cause Euler buckling of your>red blood cells of your butt. This results in better oxygen delivery and hence>less discomfort. The claim that it also improves you speed is however false.
And it's not effective in the older. "blue blood" family lines of certain eastern states. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts.
Jhas wrote:> After last week's lively and informative discussion re "Cabon Fiber> Seat Stays = Better Ride?" I feel compelled to ask: can the same be> said for S-bend seat and chain stays? Lots of manufacturers claim> that s-bend stays add "vertical compliance" or increase lateral> stiffness. I'm having a difficult time believing any of it.
My bike has carbon seat stays and rides real nice.
My bike doesn't have any S-stays and rides real nice.
Therefore, carbon stays are worthwhile and S-stays are useless gimmicks.
"jtaylor" wrote: (clip) a straight tube is stronger, and so a curved tube if not to be weaker must be heavier. (clip) ^^^^^^^^^^^^ Furthermore, making the tube heavier to keep the needed strength reduces the compliance, so even that tiny advantage is largely lost.
(clip) a straight tube is stronger, and so a curved tube if not to>> be weaker must be heavier. (clip)
Furthermore, making the tube heavier to keep the needed strength> reduces the compliance, so even that tiny advantage is largely lost.
Furhtermore, where in machinery do we find a buckling compression spring to cushion vibration, either with a slight buckling initiating S-bend or a carbon fiber.
jim beam wrote: ----8<---cut bent stays are essentially> pre-buckled. imo, bent seat stays are good, bent chain stays are bad.>
Can't resist this one - what advantage would Colnago's C40/50 fish lips chain stays have, then? Apart from marketing gimmick, as was discussed earlier last year ... /Robert
David L. Johnson 19 April 2005 00:55:22 [ permanent link ]
On Mon, 18 Apr 2005 07:13:19 -0700, jim beam wrote:
David L. Johnson wrote:
That is certainly reassuring, to imagine that curved stays are "buckled". >> The advantages are what, exactly? I had an old fork that was locally>> euler buckled after a crash. Perhaps I should have kept that, but somehow>> I thought that would be a bad idea.>>
that's bent, as in bending beam, not compression buckled, per euler. > but i guess engineering was not your point.
Actually, a "bent" tube would be compression buckled -- at least my fork was.
--
David L. Johnson
__o | It is a scientifically proven fact that a mid life crisis can _`\(,_ | only be cured by something racy and Italian. Bianchis and (_)/ (_) | Colnagos are a lot cheaper than Maserattis and Ferraris. -- Glenn Davies
(clip) a straight tube is stronger, and so a curved tube if not to>>> be weaker must be heavier. (clip)
Furthermore, making the tube heavier to keep the needed strength>> reduces the compliance, so even that tiny advantage is largely>> lost.
Furthermore, where in machinery do we find a buckling compression> spring to cushion vibration, either with a slight buckling> initiating S-bend or a carbon fiber.
And yet further, buckling is a highly unstable failure that, once initiated, accelerates to complete collapse if the column is not unloaded in the process. Therefore, this would be a useless means of furnishing give in an element under compression load.
David L. Johnson wrote:> On Mon, 18 Apr 2005 07:13:19 -0700, jim beam wrote:>
David L. Johnson wrote:>
That is certainly reassuring, to imagine that curved stays are "buckled". >>>The advantages are what, exactly? I had an old fork that was locally>>>euler buckled after a crash. Perhaps I should have kept that, but somehow>>>I thought that would be a bad idea.>>>
that's bent, as in bending beam, not compression buckled, per euler. >>but i guess engineering was not your point.>
Actually, a "bent" tube would be compression buckled -- at least my fork> was.>
it's only buckled if the force was axial. most forks simply bend because crash forces are primarily at 20-odd degrees to the fork's perpendicular.
jobst.brandt@stanfordalumni.org wrote:> I wrote:>
(clip) a straight tube is stronger, and so a curved tube if not to>>>>be weaker must be heavier. (clip)>
Furthermore, making the tube heavier to keep the needed strength>>>reduces the compliance, so even that tiny advantage is largely>>>lost.>
Furthermore, where in machinery do we find a buckling compression>>spring to cushion vibration, either with a slight buckling>>initiating S-bend or a carbon fiber.>
And yet further, buckling is a highly unstable failure that, once> initiated, accelerates to complete collapse if the column is not> unloaded in the process. Therefore, this would be a useless means of> furnishing give in an element under compression load.>
Jobst.Brandt@stanfordalumni.org
with an unconstrained load that exceeds the loading capacity, yes, but with a constrained load that does not exceed bucking, then it doesn't!!! you're really stretching to make your facts fit your friction today aren't you.
After last week's lively and informative discussion re "Cabon Fiber>>Seat Stays = Better Ride?" I feel compelled to ask: can the same be>>said for S-bend seat and chain stays? Lots of manufacturers claim>>that s-bend stays add "vertical compliance" or increase lateral>>stiffness. I'm having a difficult time believing any of it.>
My bike has carbon seat stays and rides real nice.>
My bike doesn't have any S-stays and rides real nice.>
Therefore, carbon stays are worthwhile and S-stays are useless gimmicks.>
HTH, BS>
my aluminum frame with straight stays is a brute. my aluminum frame with curved stays is like a big old sofa. same saddle, wheels, etc. go figure.
David L. Johnson 19 April 2005 08:44:28 [ permanent link ]
On Mon, 18 Apr 2005 20:22:35 -0700, jim beam wrote:
that's bent, as in bending beam, not compression buckled, per euler. >>>but i guess engineering was not your point.>>
Actually, a "bent" tube would be compression buckled -- at least my fork>> was.>>
it's only buckled if the force was axial. most forks simply bend > because crash forces are primarily at 20-odd degrees to the fork's > perpendicular.
I don't think so. A typical bent tube will exhibit crumpling on the inside, and little if any damage on the other side. That's because the material is more difficult to stretch than it is to buckle the tube. A solid beam will behave differently.
David L. Johnson wrote:> On Mon, 18 Apr 2005 20:22:35 -0700, jim beam wrote:>
that's bent, as in bending beam, not compression buckled, per euler. >>>>but i guess engineering was not your point.>>>
Actually, a "bent" tube would be compression buckled -- at least my fork>>>was.>>>
it's only buckled if the force was axial. most forks simply bend >>because crash forces are primarily at 20-odd degrees to the fork's >>perpendicular.>
I don't think so. A typical bent tube will exhibit crumpling on the> inside, and little if any damage on the other side. That's because the> material is more difficult to stretch than it is to buckle the tube. A> solid beam will behave differently.>
what you describe is tube collapse - a function of wall thickness, not typical 1st or 3rd order euler.
What is also often skipped is the fact that a straight tube is stronger, and>> so a curved tube if not to be weaker must be heavier.>>
And _that_ difference is orders of magnitude greater than any extra>> "compliance".>>
that's actually a good point. and it gets to the heart of the issue. >it allows the builder to tailor the compliance to give the desired ride. > a straight stay in pure compression gives no such option.
Jim, you're hereby promoted to grand poobah of marketing mumbo-jumbo. Congratulations. You should do well and sell lots o' bikes to those who believe you.
On Mon, 18 Apr 2005 20:39:48 -0700, jim beam <nospam@example.net> wrote:
Bill Sornson wrote:>> Jhas wrote:>>
After last week's lively and informative discussion re "Cabon Fiber>>>Seat Stays = Better Ride?" I feel compelled to ask: can the same be>>>said for S-bend seat and chain stays? Lots of manufacturers claim>>>that s-bend stays add "vertical compliance" or increase lateral>>>stiffness. I'm having a difficult time believing any of it.>>
My bike has carbon seat stays and rides real nice.>>
My bike doesn't have any S-stays and rides real nice.>>
Therefore, carbon stays are worthwhile and S-stays are useless gimmicks.>>
HTH, BS>>
my aluminum frame with straight stays is a brute. my aluminum frame >with curved stays is like a big old sofa. same saddle, wheels, etc. go >figure.
I just acquired a Klein mountain bike.
Anybody have comments on their practice of squaring the chainstays at the BB end. They insist this is for compliance and comfort. It seems plausible to me as making a hell of a lot more difference than bending round stays.
Anybody have comments on their practice of squaring the chainstays> at the BB end. They insist this is for compliance and comfort. It> seems plausible to me as making a hell of a lot more difference than> bending round stays.
The "rear triangle" of a bicycle is a tetrahedron and has linear forces at its junctions (other than the bending load of the seat post). That means the structure is loaded in tension and compression. The cross section of the elements of such a structure are ideally round tubes because they have the greatest resistance to buckling for their weight. That is why seat and chain stays are classically round and far thinner than the main tubes that support torsion and bending.
Other tube shapes, be they square or clover-leaf shaped are fads.
After last week's lively and informative discussion re "Cabon Fiber>>> Seat Stays = Better Ride?" I feel compelled to ask: can the same be>>> said for S-bend seat and chain stays? Lots of manufacturers claim>>> that s-bend stays add "vertical compliance" or increase lateral>>> stiffness. I'm having a difficult time believing any of it.>>
my aluminum frame with straight stays is a brute. my aluminum frame > with curved stays is like a big old sofa. same saddle, wheels, etc. go > figure.
Curious. In another, related thread, Jim stated that carbon fiber stays have more damping, so therefore they must contribute to additional ride comfort. And yet ... aluminum has more damping than steel (according the data in this web page referenced below, aluminum has a damping coefficient 10 times as great as steel), but aluminum frames are claimed to ride harsher than steel. How can this be?
Could it be that the aluminum stays are far too stiff for any its material damping to matter? And if so, why shouldn't that apply to carbon fiber stays?
Or perhaps there is another possibility, as raised in another recent thread - could Jim be BS-ing us, with no concern for the truth or deception?
As a short anecdote, I have several bikes, including one with a titanium frame, one with a "traditional" steel (Columbus SLX) frame, and one with oversized aluminum (all with straight stays). The one that is the most comfortable to ride is the one with the oversized aluminum frame. I should also add that the oversized aluminum frame has the fattest tires and the longest wheelbase.
Mark Hickey wrote:> jim beam <nospam@example.net> wrote:>
jtaylor wrote:>
What is also often skipped is the fact that a straight tube is stronger, and>>>so a curved tube if not to be weaker must be heavier.>>>
And _that_ difference is orders of magnitude greater than any extra>>>"compliance".>>>
that's actually a good point. and it gets to the heart of the issue. >>it allows the builder to tailor the compliance to give the desired ride. >> a straight stay in pure compression gives no such option.>
Jim, you're hereby promoted to grand poobah of marketing mumbo-jumbo.> Congratulations. You should do well and sell lots o' bikes to those> who believe you.>
David L. Johnson 20 April 2005 06:26:26 [ permanent link ]
On Tue, 19 Apr 2005 23:34:28 +0000, Mark McMaster wrote:
with straight stays). The one that is the most comfortable > to ride is the one with the oversized aluminum frame. I > should also add that the oversized aluminum frame has the > fattest tires and the longest wheelbase.
Yes, you should. I'm "sure" that won't have any effect on comfort, though, and it's just those cushy seatstays....
--
David L. Johnson
__o | You will say Christ saith this and the apostles say this; but _`\(,_ | what canst thou say? -- George Fox. (_)/ (_) |
After last week's lively and informative discussion re "Cabon Fiber>>>> Seat Stays = Better Ride?" I feel compelled to ask: can the same be>>>> said for S-bend seat and chain stays? Lots of manufacturers claim>>>> that s-bend stays add "vertical compliance" or increase lateral>>>> stiffness. I'm having a difficult time believing any of it.>>>
my aluminum frame with straight stays is a brute. my aluminum frame >> with curved stays is like a big old sofa. same saddle, wheels, etc. >> go figure.>
Curious. In another, related thread, Jim stated that carbon fiber stays > have more damping, so therefore they must contribute to additional ride > comfort. And yet ... aluminum has more damping than steel (according > the data in this web page referenced below, aluminum has a damping > coefficient 10 times as great as steel), but aluminum frames are claimed > to ride harsher than steel. How can this be?>
Could it be that the aluminum stays are far too stiff for any its > material damping to matter? And if so, why shouldn't that apply to > carbon fiber stays?>
Or perhaps there is another possibility, as raised in another recent > thread - could Jim be BS-ing us, with no concern for the truth or > deception?
or maybe the originator of that thread suceeded in thir intent of muddying the water.
As a short anecdote, I have several bikes, including one with a titanium > frame, one with a "traditional" steel (Columbus SLX) frame, and one with > oversized aluminum (all with straight stays). The one that is the most > comfortable to ride is the one with the oversized aluminum frame. I > should also add that the oversized aluminum frame has the fattest tires > and the longest wheelbase.
hmm. both mine are 410mm, same wheel & tire. same seat post & saddle too.
"A bicycle frame is basically a bridge truss, with almost no vertical> deflection. To put this in perspective, imagine supporting a bare frame> by the head tube and rear dropouts on two large concrete blocks. Now,> straddle the frame and jump onto the top tube. Ouch! What happened? You> just discovered that the frame doesn't really flex very much in a> vertical plane. The total deflection will only be a small percentage> (around 3%) of the flex available in the bike "system", including> tires, wheels, stem, handlebars, and saddle. As a result, adding or> subtracting 5psi from your tires is likely to make more difference in> comfort than going from the softest to the stiffest possible frame. ">
Pretty consistent with what _most_ people are saying in this> discussion. Pretty consistent with physics, as well.>
"Remember, vibration isolation in the system will occur above fn [i.e.> the natural frequency of the isolation mount and supported system]. ...> As a rule of thumb, the natural frequency of the mounting system should> be one-third of the frequency of concern.">
Your task, Jim, is to explain how the relatively stiff carbon stay,> which would have a natural frequency up in the acoustic range, manages> to damp the relatively low frequencies that make up typical road buzz> and shocks.>
While you're at it, you might explain how those high frequencies are> _not_ isolated from the carbon tube itself by the low-natural-frequency> system comprising the tire, the seat, and the rider's mass.>
The trick is, of course, to do this without invoking magic! >
- Frank Krygowski>
you buy that balloon yet frank? what were your results? or was i tricking you?
"jim beam" <nospam@example.net> wrote in message news:1113966456.79ef75508f99be0c65c7a4659e95a795@teranews...> frkrygow@yahoo.com wrote:> > jim beam wrote:> >
"A bicycle frame is basically a bridge truss, with almost no vertical> > deflection. To put this in perspective, imagine supporting a bare frame> > by the head tube and rear dropouts on two large concrete blocks. Now,> > straddle the frame and jump onto the top tube. Ouch! What happened? You> > just discovered that the frame doesn't really flex very much in a> > vertical plane. The total deflection will only be a small percentage> > (around 3%) of the flex available in the bike "system", including> > tires, wheels, stem, handlebars, and saddle. As a result, adding or> > subtracting 5psi from your tires is likely to make more difference in> > comfort than going from the softest to the stiffest possible frame. "> >
Pretty consistent with what _most_ people are saying in this> > discussion. Pretty consistent with physics, as well.> >
"Remember, vibration isolation in the system will occur above fn [i.e.> > the natural frequency of the isolation mount and supported system]. ...> > As a rule of thumb, the natural frequency of the mounting system should> > be one-third of the frequency of concern."> >
Your task, Jim, is to explain how the relatively stiff carbon stay,> > which would have a natural frequency up in the acoustic range, manages> > to damp the relatively low frequencies that make up typical road buzz> > and shocks.> >
While you're at it, you might explain how those high frequencies are> > _not_ isolated from the carbon tube itself by the low-natural-frequency> > system comprising the tire, the seat, and the rider's mass.> >
The trick is, of course, to do this without invoking magic! > >
- Frank Krygowski> >
you buy that balloon yet frank? what were your results? or was i> tricking you?>
Hey - I read all that stuff above thinking you were going to answer the question, and you blew it!
Anybody have comments on their practice of squaring the chainstays>>> at the BB end. They insist this is for compliance and comfort. It>>> seems plausible to me as making a hell of a lot more difference>>> than bending round stays.
The "rear triangle" of a bicycle is a tetrahedron and has linear>> forces at its junctions (other than the bending load of the seat>> post). That means the structure is loaded in tension and>> compression. The cross section of the elements of such a structure>> are ideally round tubes because they have the greatest resistance>> to buckling for their weight. That is why seat and chain stays are>> classically round and far thinner than the main tubes that support>> torsion and bending.
Other tube shapes, be they square or clover-leaf shaped are fads.
The problem with round chainstays is that they don't fit between the> tire and the inner chainring, unless they are so thin as to be too> flexible sideways. This was traditionally solved by either> ovalizing or crimping (denting) the stay at this point. Among frame> builders it was debatable which method produced a laterally stiffer> frame. My theory was that the crimped stay was stiffer because it> had a more horizontally oriented cross-section than the more> vertically oriented oval. Klein developed this principle further> with the square section chainstay. It provides the largest> cross-section that will still fit and has the highest horizontal> stiffness-to-weight ratio.
I don't believe lateral stiffness enters into the rear triangle, that stiffness being generally how far the bottom bracket deflects laterally when pushing on one pedal (in some prescribed manner). This deflection is more a torsional elasticity of top and downtube together with bending stiffness at the bottom end of the seat tube.
The 'rear triangle' has little to do with this where the crimp is a way of gaining clearance without losing material in the walls of these tubes that are stressed in tension and compression. The chainstays need to be larger in diameter than the seat stays to avoid buckling at midspan, the right stay having more than four times the static compression load of a seatstay. Of course, road shock loads can be higher, and that depends on use and has been pragmatically determined.
I don't believe lateral stiffness enters into the rear triangle, that> stiffness being generally how far the bottom bracket deflects> laterally when pushing on one pedal (in some prescribed manner). This> deflection is more a torsional elasticity of top and downtube together> with bending stiffness at the bottom end of the seat tube.
I know you will not appreciate this reference, but you really should look at the tests done by le Cycle. They isolate head tube, bottom bracket and rear triangle for deflection measurements. Perhaps you would disagree with their methodology, but that would mean you looked at it first. Each frame tested over many years already is subjected to this testing procedure, without variation, and the results are there for you to examine. I believe they also publish an annual recapitulation of these results, should you want to find out more about a phenomenon that you declare does not exist. Or did I misread you ?
Should you have an interest in this, I would be happy to cut out the tests from a few issues and send them to you (thereby not violating IP law), so you could have a broader base of knowledge. It would save me annoying you with these references.
"A bicycle frame is basically a bridge truss, with almost
vertical> > > deflection. To put this in perspective, imagine supporting
a bare> frame> > > by the head tube and rear dropouts on two large concrete blocks.> Now,> > > straddle the frame and jump onto the top tube. Ouch! What happened?> You> > > just discovered that the frame doesn't really flex very much in a> > > vertical plane. The total deflection will only be a small> percentage> > > (around 3%) of the flex available in the bike "system", including> > > tires, wheels, stem, handlebars, and saddle. As a result, adding or> > > subtracting 5psi from your tires is likely to make more difference> in> > > comfort than going from the softest to the stiffest possible frame.> "> > >
Pretty consistent with what _most_ people are saying in
this> > > discussion. Pretty consistent with physics, as well.> > >
"Remember, vibration isolation in the system will occur
above fn> [i.e.> > > the natural frequency of the isolation mount and supported system].> ...> > > As a rule of thumb, the natural frequency of the mounting system> should> > > be one-third of the frequency of concern."> > >
Your task, Jim, is to explain how the relatively stiff
carbon stay,> > > which would have a natural frequency up in the acoustic range,> manages> > > to damp the relatively low frequencies that make up typical road> buzz> > > and shocks.> > >
While you're at it, you might explain how those high
frequencies> are> > > _not_ isolated from the carbon tube itself by the> low-natural-frequency> > > system comprising the tire, the seat, and the rider's mass.> > >
The trick is, of course, to do this without invoking magic!
> > >
- Frank Krygowski> > >
you buy that balloon yet frank? what were your results? or
was i> > tricking you?>
Seems to me you're tricking yourself.>
Which is it, Jim - do the seatstays violate physical laws by
damping> vibrations that are many times lower than physics predicts? Or do the> tires and saddle violate physics by passing vibrations which are many> times higher than physics permits?
Has anyone done testing? It seems to me that it would be easy to test whether stay material or stay design has any effect on vibration dampening. Considering that this is a frequent claim by manufacturers -- and apparently has achieved the status of truth in the bicycling industry -- I assume that someone has done at least a little testing. I was leafing through the Velo News article on the new Cannondale Synapse CF frame, and it said that the rear triangle design (wavy stays) allowed 70mm of travel -- or at least that is how I read the article. I dont't have it with me, though. -- Jay Beattie.
Has anyone done testing? It seems to me that it would be easy to>test whether stay material or stay design has any effect on>vibration dampening. Considering that this is a frequent claim>by manufacturers -- and apparently has achieved the status of>truth in the bicycling industry -- I assume that someone has done>at least a little testing. I was leafing through the Velo News>article on the new Cannondale Synapse CF frame, and it said that>the rear triangle design (wavy stays) allowed 70mm of travel -- >or at least that is how I read the article. I dont't have it>with me, though. -- Jay Beattie.>
Dear Jay,
Since 70 mm is about 2 & 3/4 inches, I expect that either you're mis-remembering the travel or the frame is a rear-suspension design with spring and damper.
As for the vibration testing that you have in mind, it seems to involve an accelerometer and people who know how to use it. I've been watching the Harbor Freight tool sales, but they don't seem to be pushing such items.
You'd probably want a portable, self-contained multiple-axis accelerometer. Maybe the automotive ones would work, but they also seem to need a few accessories. Have a look at this price list:
Finding someone who knows how to set it up on a bike and use it would be even more expensive.
Considering how hard it is to find recent rolling resistance data on tires (an undisputed effect measurable by a comparatively simple but tedious test), the argument a fortiori is that we shouldn't hold our breath in hopes of expensive testing of vibration just to satisfy the insatiable curiosity of people like me, who aren't bothered by whatever our steel frames are doing as we cruise along, but would really like to know what the effect--if any--is.
That's what's nice about the internet age and an unhealthy interest in literature--anyone who wants can browse through excellent scans of million-dollar First Folios for free:
David L. Johnson 21 April 2005 01:43:25 [ permanent link ]
On Wed, 20 Apr 2005 10:56:10 -0700, Jay Beattie wrote:
I was leafing through the Velo News> article on the new Cannondale Synapse CF frame, and it said that> the rear triangle design (wavy stays) allowed 70mm of travel -- > or at least that is how I read the article. I dont't have it> with me, though. -- Jay Beattie.
On the web was this:
Triaxial Hourglass seat stays combined with Cannondale exclusive S.A.V.E technology (Synapse Active Vibration Elimination) in the chain-stays and fork provide a pinpoint balance of vibration absorbing comfort and lateral performance stiffness. The result is a bike that will turn half-hour rides into half-day rides and half-day rides into all-day excursions.
Oh, dear. This bit of ad copy is over the top, of course, but the last sentence could read as "It will take you twice as long to complete a ride". Maybe they didn't mean it that way...
--
David L. Johnson
__o | The lottery is a tax on those who fail to understand _`\(,_ | mathematics. (_)/ (_) |
I was leafing through the Velo News>article on the new Cannondale Synapse CF frame, and it said that>the rear triangle design (wavy stays) allowed 70mm of travel -- >or at least that is how I read the article. I dont't have it>with me, though. -- Jay Beattie.
Well, as long as they don't try to claim it has that much travel TWICE...
"David L. Johnson" <david.johnson@lehigh-nospam.edu> wrote:
On Wed, 20 Apr 2005 10:56:10 -0700, Jay Beattie wrote:>
I was leafing through the Velo News>> article on the new Cannondale Synapse CF frame, and it said that>> the rear triangle design (wavy stays) allowed 70mm of travel -- >> or at least that is how I read the article. I dont't have it>> with me, though. -- Jay Beattie.>
On the web was this:>
Triaxial Hourglass seat stays combined with Cannondale exclusive S.A.V.E>technology (Synapse Active Vibration Elimination) in the chain-stays
In the CHAIN STAYS??? Wow. I doubt even our own resident S-Stay fans would claim that.
fork provide a pinpoint balance of vibration absorbing comfort and lateral>performance stiffness.
Too cool - I wonder how the tube knows not to flex sideways? Smart tubes.
The result is a bike that will turn half-hour rides>into half-day rides and half-day rides into all-day excursions.
Sigh, and here I thought I was helping out supplying bikes that turn half-day rides into half-hour rides. Doesn't anyone like going fast any more? Sigh...
Oh, dear. This bit of ad copy is over the top, of course, but the last>sentence could read as "It will take you twice as long to complete a>ride". Maybe they didn't mean it that way...
"Remember, vibration isolation in the system will occur>
above fn>
[i.e.>>
the natural frequency of the isolation mount and supported>
system].>
...>>
As a rule of thumb, the natural frequency of the mounting>
system>
should>>
be one-third of the frequency of concern.">>>>
Your task, Jim, is to explain how the relatively stiff>
carbon stay,>
which would have a natural frequency up in the acoustic>
range,>
manages>>
to damp the relatively low frequencies that make up typical>
road>
buzz>>
and shocks.>>>>
While you're at it, you might explain how those high>
frequencies>
_not_ isolated from the carbon tube itself by the>>
low-natural-frequency>>
system comprising the tire, the seat, and the rider's mass.>>>>
The trick is, of course, to do this without invoking magic!>
>
- Frank Krygowski>>>>
you buy that balloon yet frank? what were your results? or>
was i>
tricking you?>>
Seems to me you're tricking yourself.>>
Which is it, Jim - do the seatstays violate physical laws by>
damping>
vibrations that are many times lower than physics predicts? Or>
do the>
tires and saddle violate physics by passing vibrations which>
are many>
times higher than physics permits?>
Has anyone done testing? It seems to me that it would be easy to> test whether stay material or stay design has any effect on> vibration dampening. Considering that this is a frequent claim> by manufacturers -- and apparently has achieved the status of> truth in the bicycling industry -- I assume that someone has done> at least a little testing. I was leafing through the Velo News> article on the new Cannondale Synapse CF frame, and it said that> the rear triangle design (wavy stays) allowed 70mm of travel -- > or at least that is how I read the article. I dont't have it> with me, though. -- Jay Beattie.>
jobst.brandt@stanfordalumni.org wrote:> Dan Christopherson writes:>
I just acquired a Klein mountain bike.>
Anybody have comments on their practice of squaring the chainstays>>>>at the BB end. They insist this is for compliance and comfort. It>>>>seems plausible to me as making a hell of a lot more difference>>>>than bending round stays.>
The "rear triangle" of a bicycle is a tetrahedron and has linear>>>forces at its junctions (other than the bending load of the seat>>>post). That means the structure is loaded in tension and>>>compression. The cross section of the elements of such a structure>>>are ideally round tubes because they have the greatest resistance>>>to buckling for their weight. That is why seat and chain stays are>>>classically round and far thinner than the main tubes that support>>>torsion and bending.>
Other tube shapes, be they square or clover-leaf shaped are fads.>
The problem with round chainstays is that they don't fit between the>>tire and the inner chainring, unless they are so thin as to be too>>flexible sideways. This was traditionally solved by either>>ovalizing or crimping (denting) the stay at this point. Among frame>>builders it was debatable which method produced a laterally stiffer>>frame. My theory was that the crimped stay was stiffer because it>>had a more horizontally oriented cross-section than the more>>vertically oriented oval. Klein developed this principle further>>with the square section chainstay. It provides the largest>>cross-section that will still fit and has the highest horizontal>>stiffness-to-weight ratio.>
I don't believe lateral stiffness enters into the rear triangle
that sounds like a "spokes don't bend at the elbow under axial load" or a "bottom brackets don't bend" argument. fact is they /do/ bend as is evidenced by fatigue - fatigue fundamentally /cannot/ exist in the absence of strain. where are two places for to frames commonly break? at the chain stay bridge and where the chain stays join the bottom bracket.
again, fatigue absolutely fundamentally evidences strain, ergo the rear triangle is flexing. of the available strain axes, the least stiff orientation is lateral. which is again [incredibly] evidenced by the orientation of these cracks!
but maybe i'm blowing smoke.
, that> stiffness being generally how far the bottom bracket deflects> laterally when pushing on one pedal (in some prescribed manner). This> deflection is more a torsional elasticity of top and downtube together> with bending stiffness at the bottom end of the seat tube. >
The 'rear triangle' has little to do with this where the crimp is a> way of gaining clearance without losing material in the walls of these> tubes that are stressed in tension and compression. The chainstays> need to be larger in diameter than the seat stays to avoid buckling at> midspan, the right stay having more than four times the static> compression load of a seatstay. Of course, road shock loads can be> higher, and that depends on use and has been pragmatically determined.>
"Remember, vibration isolation in the system will occur>>
above fn>>
[i.e.>>>
the natural frequency of the isolation mount and supported>>
system].>>
...>>>
As a rule of thumb, the natural frequency of the mounting>>
system>>
should>>>
be one-third of the frequency of concern.">>>>>
Your task, Jim, is to explain how the relatively stiff>>
carbon stay,>>
which would have a natural frequency up in the acoustic>>
range,>>
manages>>>
to damp the relatively low frequencies that make up typical>>
road>>
buzz>>>
and shocks.>>>>>
While you're at it, you might explain how those high>>
frequencies>>
_not_ isolated from the carbon tube itself by the>>>
low-natural-frequency>>>
system comprising the tire, the seat, and the rider's mass.>>>>>
The trick is, of course, to do this without invoking magic!>>
>>
- Frank Krygowski>>>>>
you buy that balloon yet frank? what were your results? or>>
was i>>
tricking you?>>>
Seems to me you're tricking yourself.>>>
Which is it, Jim - do the seatstays violate physical laws by>>
damping>>
vibrations that are many times lower than physics predicts? Or>>
do the>>
tires and saddle violate physics by passing vibrations which>>
are many>>
times higher than physics permits?>>
Has anyone done testing? It seems to me that it would be easy to>> test whether stay material or stay design has any effect on>> vibration dampening. Considering that this is a frequent claim>> by manufacturers -- and apparently has achieved the status of>> truth in the bicycling industry -- I assume that someone has done>> at least a little testing. I was leafing through the Velo News>> article on the new Cannondale Synapse CF frame, and it said that>> the rear triangle design (wavy stays) allowed 70mm of travel -- >> or at least that is how I read the article. I dont't have it>> with me, though. -- Jay Beattie.>>
An email reply today from a nice fellow named Jeff at Specialized has offered to send me a hard copy of the "Witchcraft" paper, so with luck I'll soon have a scan of the accelerometer graphs whose captions seem to be unreadable online, the ones showing something about vibration differences between the front hub and handlebars and the rear hub and seat.
If anyone else has a readable scan and wants to pre-empt me, that would be nice, too.
An email reply today from a nice fellow named Jeff at> Specialized has offered to send me a hard copy of the> "Witchcraft" paper, so with luck I'll soon have a scan of> the accelerometer graphs whose captions seem to be> unreadable online, the ones showing something about> vibration differences between the front hub and handlebars> and the rear hub and seat.>
If anyone else has a readable scan and wants to pre-empt me,> that would be nice, too.>
Carl Fogel
good move. still readable enough as-is though. two lines are still clearly distinguishable, and one is clearly above the other.
<carlfogel@comcast.net> wrote in message news:jf8d61pd33ilr6ieieotup49vcj2vrhnqb@4ax.com...> On Wed, 20 Apr 2005 10:56:10 -0700, "Jay Beattie"> <jbeattie@lindsayhart.com> wrote:>
[snip]>
Has anyone done testing? It seems to me that it would be easy
test whether stay material or stay design has any effect on> >vibration dampening. Considering that this is a frequent
claim> >by manufacturers -- and apparently has achieved the status of> >truth in the bicycling industry -- I assume that someone has done> >at least a little testing. I was leafing through the Velo News> >article on the new Cannondale Synapse CF frame, and it said that> >the rear triangle design (wavy stays) allowed 70mm of travel -- > >or at least that is how I read the article. I dont't have it> >with me, though. -- Jay Beattie.> >
Dear Jay,>
Since 70 mm is about 2 & 3/4 inches, I expect that either> you're mis-remembering the travel or the frame is a> rear-suspension design with spring and damper.
D'oh! So much for my Evelyn Wood speed reading comprehension. This is what the article says:
"The Synapse takes a page from Cannondale's Scalpel cross-country racing mountain bike in achieving compliance over rough surfaces. The SCALPEL [not the Synapse] has carbon chainstays that are flat in the horizontal plane, and they flex enough to grant the real wheel 70mm of vertical travel. WHILE THE WHEEL TRAVEL OF THE SYNAPSE IS TINY IN COMPARISON, the system is similar. On the Synapse, it's called S.A.V.E, for Synapse Active Vibration Elimination.
The S.A.V.E. chainstays have a flattened section in the middle for vertical flex, and the seatstays are curved towards the bottom bracket to allow that flex to occur. the right and left chainstays are asymmetrical to deal with different stresses and clearance issues, and the seatstays are separate and continue all the way to the seat tube (i.e. they are non-wishbone), a more expensive construction method requiring more molds but resulting lower weight and more vibration absorption, Cannondale says. They are also curved outward and inward in an hourglass shape.
The seat tube has a teardrop section over much of its length, which reduces the ability of the tube to bow and thus accommodates more vertical rear wheel movement, but Cannondale engineers designed that seat tube section not for compliance but to improve aerodynamics and looks while adding only five grams to the frame weight."
<carlfogel@comcast.net> wrote in message>news:jf8d61pd33ilr6ieieotup49vcj2vrhnqb@4ax.com...>> On Wed, 20 Apr 2005 10:56:10 -0700, "Jay Beattie">> <jbeattie@lindsayhart.com> wrote:>>
[snip]>>
Has anyone done testing? It seems to me that it would be easy>to>> >test whether stay material or stay design has any effect on>> >vibration dampening. Considering that this is a frequent>claim>> >by manufacturers -- and apparently has achieved the status of>> >truth in the bicycling industry -- I assume that someone has>done>> >at least a little testing. I was leafing through the Velo>News>> >article on the new Cannondale Synapse CF frame, and it said>that>> >the rear triangle design (wavy stays) allowed 70mm of>travel -- >> >or at least that is how I read the article. I dont't have it>> >with me, though. -- Jay Beattie.>> >
Dear Jay,>>
Since 70 mm is about 2 & 3/4 inches, I expect that either>> you're mis-remembering the travel or the frame is a>> rear-suspension design with spring and damper.>
D'oh! So much for my Evelyn Wood speed reading comprehension.>This is what the article says:>
"The Synapse takes a page from Cannondale's Scalpel cross-country>racing mountain bike in achieving compliance over rough surfaces.>The SCALPEL [not the Synapse] has carbon chainstays that are flat>in the horizontal plane, and they flex enough to grant the real>wheel 70mm of vertical travel. WHILE THE WHEEL TRAVEL OF THE>SYNAPSE IS TINY IN COMPARISON, the system is similar. On the>Synapse, it's called S.A.V.E, for Synapse Active Vibration>Elimination.>
The S.A.V.E. chainstays have a flattened section in the middle>for vertical flex, and the seatstays are curved towards the>bottom bracket to allow that flex to occur. the right and left>chainstays are asymmetrical to deal with different stresses and>clearance issues, and the seatstays are separate and continue all>the way to the seat tube (i.e. they are non-wishbone), a more>expensive construction method requiring more molds but resulting>lower weight and more vibration absorption, Cannondale says.>They are also curved outward and inward in an hourglass shape.>
The seat tube has a teardrop section over much of its length,>which reduces the ability of the tube to bow and thus>accommodates more vertical rear wheel movement, but Cannondale>engineers designed that seat tube section not for compliance but>to improve aerodynamics and looks while adding only five grams to>the frame weight.">
-- Jay Beattie.
Dear Jay,
Since the article that you quote is a little unclear, it's worth pointing out that the Cannondale Scalpel's carbon chainstays attach to seatstays that link to a Fox airspring suspension unit:
David L. Johnson 22 April 2005 05:02:26 [ permanent link ]
On Thu, 21 Apr 2005 08:39:21 -0700, Jay Beattie wrote:
D'oh! So much for my Evelyn Wood speed reading comprehension.> This is what the article says:>
"The Synapse takes a page from Cannondale's Scalpel cross-country> racing mountain bike in achieving compliance over rough surfaces.> The SCALPEL [not the Synapse] has carbon chainstays that are flat> in the horizontal plane, and they flex enough to grant the real> wheel 70mm of vertical travel. WHILE THE WHEEL TRAVEL OF THE> SYNAPSE IS TINY IN COMPARISON, the system is similar.
Horseshit. How is a FS mountain bike similar to an unsuspended road bike?
--
David L. Johnson
__o | Let's not escape into mathematics. Let's stay with reality. -- _`\(,_ | Michael Crichton (_)/ (_) |
