S-bend stays?

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.

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" wrote in message
ups.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.

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
(_)/ (_) |

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.

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.

What Jim writes above is in line with his theology, but could give
those who may be willing to spend a considerable amount of their
hard-earned on S-stays the wrong impression. That is, that they would
get a noticeably better ride from a bike with S-stays.

FWIW, I sell frames/bikes with and without S-stays (and get more money
for the ones with S-stays). But I go out of my way to ensure that I
don't ever give anyone the impression that an S-stay would make a
noticeable difference in ride quality. I'm not aware of any frame out
there with a radical enough "S" stay that it would act like anything
other than a straight stay in any meaningful way.

Jim also misses the fact that S-shaped chainstays DO make sense in
terms of heel clearance (for those who pedal heel-in) and tire
clearance. I'm not aware of any real performance improvement with an
S-shaped seat stay, though they do look kinda sexy.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

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" wrote in message
ups.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...

On 18 Apr 2005 05:49:34 -0700, "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.

Hetchins supposedly did it because British amateur racing rules didn't permit
large identification badges on bikes and wanted brand recognition.

Ya know, tubes make such crap springs in anything other than torsion I wouldn't
really expect it to work.

Ron

In article 1113829678.ff940e043a380ff9b29ac0028169990d@teran ews, 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.

Hetchins supposedly did it because British amateur racing rules didn't
permit
large identification badges on bikes and wanted brand recognition.

Ya know, tubes make such crap springs in anything other than torsion I
wouldn't
really expect it to work.

The Hetchins story isn't really true. There are plenty of oddball
English frame designs that play more on the English love of the odd
than marketing or engineering.
Phil Brown