Measuring "comfort" in bicycle frames?

Currently I'm helping out a Danish cycling magazine with setting up a testing facility to measure
stiffness in bicycle frames - similar to how German Tour Magazin tests (BB and headtube stiffness,
respectively). We would like to measure the frames ability to absorb shock as well.

I talked to a few engineers regarding this and they all told different stories. One said it's all
about frequency: you apply vibration with a certain frequency to the frame and measure the frequency
on the frame. Same frequency = zero dampening.

Another guy said it's a lot more complicated and that there's no simple way of measuring this.
However, measuring deflection (dunno if it's the correct term for this, hope you understand) only is
the way to go, if it has to be simple. Trad. steel frames are generally considered comfortable but
steel has the worst dampening caracteristics of all construction materials, so the comfort must come
from deflection of the thin diametre tubes.

Comments, please!

Wbr, Anders B. Bystrup Denmark

- hoping that Jobst Brandt or other experts of this newsgroup will share their knowledge

"Anders Bro Bystrup" <andersbrobystrup@hotmail.com> wrote in message
news:3f94d605$0$21490$ba624c82@nntp03.dk.telia.net...
> Currently I'm helping out a Danish cycling magazine with setting up a testing facility to measure
> stiffness in bicycle frames - similar to how German Tour Magazin tests (BB and headtube stiffness,
> respectively). We would like to measure the frames ability to absorb shock as well.
>
> I talked to a few engineers regarding this and they all told different stories. One said it's all
> about frequency: you apply vibration with a certain frequency to the frame and measure the
> frequency on the frame.
Same
> frequency = zero dampening.
>
> Another guy said it's a lot more complicated and that there's no simple
way
> of measuring this. However, measuring deflection (dunno if it's the
correct
> term for this, hope you understand) only is the way to go, if it has to be simple. Trad. steel
> frames are generally considered comfortable but steel has the worst dampening caracteristics of
> all construction materials, so
the
> comfort must come from deflection of the thin diametre tubes.
>
> Comments, please!
>
> Wbr, Anders B. Bystrup Denmark
>
> - hoping that Jobst Brandt or other experts of this newsgroup will share their knowledge

How about the hammer test; either the tyre is hit by a hammer, or bike is set on a plate which is
hit by hammer, and then the amplitudes, accelerations and frequencies are measured on the bike
saddle, pedals and handlebars?

Obviously tyres, saddle paddings and handelebar tapes are dumpening most of the vibrations, but as
bikes are normally ridden with those, they should be included in the measurements.

Antti

"Antti" <antti@no.spam> wrote in message news:QN4lb.735$k4.16509@news1.nokia.com...

> How about the hammer test; either the tyre is hit by a hammer, or bike is set on a plate which is
> hit by hammer, and then the amplitudes, accelerations and frequencies are measured on the bike
> saddle, pedals and handlebars?
>
> Obviously tyres, saddle paddings and handelebar tapes are dumpening most
of
> the vibrations, but as bikes are normally ridden with those, they should
be
> included in the measurements.

We are interested in measuring frames only. Frames and bikes will be ridden as a part of the tests
but we want to add measureable facts to the subjective riding impression.

Wbr, Anders

"Anders Bro Bystrup" <andersbrobystrup@hotmail.com> wrote in message
news:3f94e1dc$0$21483$ba624c82@nntp03.dk.telia.net...
>
> "Antti" <antti@no.spam> wrote in message news:QN4lb.735$k4.16509@news1.nokia.com...
>
> > How about the hammer test; either the tyre is hit by a hammer, or bike
is
> > set on a plate which is hit by hammer, and then the amplitudes, accelerations and frequencies
> > are measured on the bike saddle, pedals
and
> > handlebars?
> >
> > Obviously tyres, saddle paddings and handelebar tapes are dumpening most
> of
> > the vibrations, but as bikes are normally ridden with those, they should
> be
> > included in the measurements.
>
> We are interested in measuring frames only. Frames and bikes will be
ridden
> as a part of the tests but we want to add measureable facts to the subjective riding impression.
>
> Wbr, Anders

Well, then just make the measurements without bike components, but I wouldn't then recommend to make
predictions or judgements about the frame "comfort" without the related stuff. Or, might be worth to
make measurements with frames only, and normally equipped bikes?

Antti

On Tue, 21 Oct 2003 08:45:27 +0200, Anders Bro Bystrup wrote:

> We would like to measure the frames ability to absorb shock as well.

That concept is a creature of the marketing department, not engineering.

> I talked to a few engineers regarding this and they all told different stories. One said it's all
> about frequency: you apply vibration with a certain frequency to the frame and measure the
> frequency on the frame. Same frequency = zero dampening.

That's amusing. Wrong, but amusing. In a classical spring-mass-damper system, the motion of the
system (frequency of the frame) if _undamped_ will be a superposition of the natural frequency of
the system itself and the input frequency. If the input frequency matches the natural frequency
of the spring, you get resonance, a steady build-up of amplitude. If the frequencies are close
(input and natural) you get "beats", fluctuations of amplitude, like hitting two neighboring keys
of a piano.

If the system _is_ damped, then the frequency of the response will settle down to that of the input,
with an amplitude and phase shift.

This is very basic differential equations stuff.

Now, a bike frame isn't quite a simple spring-mass system, but to first order it is. The best way to
find the natural frequencies of the system is to look for resonance response by varying the input
frequency; you still get some resonance even with a damped system. No real structure is totally
undamped, just like no circuit is resistance-free.

--

David L. Johnson

__o | Accept risk. Accept responsibility. Put a lawyer out of _`\(,_ | business. (_)/ (_) |

On Tue, 21 Oct 2003, David L. Johnson wrote:
> On Tue, 21 Oct 2003 08:45:27 +0200, Anders Bro Bystrup wrote:
> > We would like to measure the frames ability to absorb shock as well.
> That concept is a creature of the marketing department, not engineering.
> > I talked to a few engineers regarding this and they all told different stories. One said it's
> > all about frequency: you apply vibration with a certain frequency to the frame and measure the
> > frequency on the frame. Same frequency = zero dampening.
> That's amusing. Wrong, but amusing....
...
> This is very basic differential equations stuff.

Confirmed, if need be. Setting aside the beauty of non-homogeneous differential equations I believe
one should take a much more prosaic attitude. I have long had an idea of how to assess comfort, and
in a way to 'measure' it. Here is how.

Take two different frames, build them into bicycles with exactly the same components, from tyres to
seat. Let the same guy ride them asking him to carry out a 'blind test'. The two bikes should have
tyres inflated to a somewhat different pressure, one bike from the other, in a way that, say, the
conventional steel frameset would feel just as mushy as the carbon fiber one.

There you have it. The two frames have become equally shock absorbing thanks to the different air
pressure in the tubes. Hence, the difference in the rolling resistence, which is a known function of
the pressure, is a measure of the ability to absorb shocks.

Isn't that all that one might want to measure, after all?

Sergio Pisa

Anders Bro Bystrup writes:

> We are interested in measuring frames only. Frames and bikes will be ridden as a part of the tests
> but we want to add measurable facts to the subjective riding impression.

I think you should do a "library search" to avoid repeating what has already been done. Besides
that, I would be interested in the goals of the research. Why and for what reason is frame stiffness
being researched? What effects of frame stiffness on riding are defined?

As mentioned in other threads on this subject, ride comfort does not come from frame flexibility but
rather its wheelbase, saddle position between front and rear wheels and handlebar position. The fork
of a bicycle is angled to receive significant (occurrence times amplitude) axially. Therefore the
fork can be ruled out as well as the rear triangle. That leaves only the flex in top and downtube.
That is easily measured by applying a static load.

Lateral stiffness, the one most often discussed, is simple to quantify by anchoring the frame by its
dropouts on horizontally rotatable swivels and putting a side load on the BB. To make a doctoral
thesis of this is ridiculous. The University of Aachen together with Tour Magazine make more of this
than there is in my estimation.

It almost rings of the old saw that steel frames get soft with use.

Jobst Brandt jobst.brandt@stanfordalumni.org

"Mike S." <mikeshaw2@coxDOTnet> wrote in message news:E4dlb.71850$vj2.9970@fed1read06...
|
...snip
|
| The best way I can think of it to get frames made of different materials
in
| the same size and angles. That way, the only thing that changes is the material, not the rider's
| positioning on the bike itself.
|
| The best way to do the test is to have the same set of components put on
all
| the bikes. Run 32 hole Open Pros, with brand X tires inflated to the
same
| PSI, the same saddle, etc. That way, you isolate the way the frame
reacts
| vs. the components.
|
...snip
|
| Mike
|
|

I vaguely remember some magazine's shoot-out between frame materials. I think the biking mag
did exactly what you are suggesting (ie, built bikes with similar geometry and size out of
different metals). Darned if I can recall the results though. Maybe someone else here can
remember the details.

Jean

Phil Brown <philcycles@aol.communged> wrote:
> >We are interested in measuring frames only. Frames and bikes will be ridden as a part of the
> >tests but we want to add measureable facts to the subjective riding impression.

> This seems like a troll but your tests will be meaningless. You don't ride frames, you ride
> bicycles and as a result your tests will have no meaning.

> Besides, how do you quantify "Comfort?"

In units of comfort, of course! The SI (Systeme Internationale) unit of comfort is the "jobst."
For obscure historical reasons comfort is measured inversely to the usual meaning (darn those
French engineers) and one jobst is about equal to Sheldon's Real Man Saddle, much too large for
everyday use, like Farads. Frame comfort engineers generally speak in terms of millijobsts,
although there are persistent rumors that Colnago is coming out with a frame that will break the
microjobst barrier.

Might have been the Rinard Frame Deflection Test by Damon Rinard
http://www.sheldonbrown.com/rinard_frametest.html

but I have to agree with Jobst Brandt, What effects of frame stiffness on riding are defined? I have
to believe measuring comfort in a bicycle frame is measured by the person riding the bike. 10
riders, 10 different opinions. -tom

"Jean" <Jean@spam.not> wrote in message news:gQelb.682$iV3.17881@eagle.america.net...
>
> I vaguely remember some magazine's shoot-out between frame materials. I think the biking mag did
> exactly what you are suggesting (ie, built bikes with similar geometry and size out of different
> metals). Darned if I can recall the results though. Maybe someone else here can remember the
> details.
>
>
> Jean

> ...snip
> |
> | The best way I can think of it to get frames made of different materials
> in
> | the same size and angles. That way, the only thing that changes is the material, not the rider's
> | positioning on the bike itself.
> |
> | The best way to do the test is to have the same set of components put on
> all
> | the bikes. Run 32 hole Open Pros, with brand X tires inflated to the
> same
> | PSI, the same saddle, etc. That way, you isolate the way the frame
> reacts
> | vs. the components.
> |
> ...snip
> |
> | Mike
> |
> |
>
> I vaguely remember some magazine's shoot-out between frame materials. I think the biking mag did
> exactly what you are suggesting (ie, built bikes with similar geometry and size out of different
> metals). Darned if I can recall the results though. Maybe someone else here can remember the
> details.
>
>
> Jean
>
IIRC it was Bicycle Guide. Again, IIRC, all they did was test different steel frames. Now that
there's other things out there than steel, I'd like to see the test done again.

I'm curious to see what "the experts" think of the new materials.

Mike

<Snip>
> We easily confuse what we hear with what we feel (which may explain why we misunderstand each
> other so often on rec.bicycles.tech.)
>
> Carl Fogel

Some just want to misunderstand. Gets them all excited to argue with people...

Mike

Jean wrote:

> I vaguely remember some magazine's shoot-out between frame materials. I think the biking mag did
> exactly what you are suggesting (ie, built bikes with similar geometry and size out of different
> metals). Darned if I can recall the results though. Maybe someone else here can remember the
> details.

Yes, the "experts" pontificated but couldn't guess which was which, even knowing what materials were
in the selection, after riding. They gave the #1 rank to the Thron bike.

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

> I vaguely remember some magazine's shoot-out between frame materials. I think the biking mag did
> exactly what you are suggesting (ie, built bikes with similar geometry and size out of different
> metals). Darned if I can recall the results though. Maybe someone else here can remember the
> details.
>
>
> Jean
>

In 'RoadBike Action', May 1995, Vol. 3, Nr. 5, p. 12-31, ISSN 1069-2648, 'The Ultimate Road Bike
Shootout' was made with 5 'identical' bikes made by a Harry Havnoonian in the different materials,
steel, aluminium, titanium, carbon fiber and metal matrix.

----
Jan Kloster Staunstrup GIM-lab. Aalborg University, Denmark.

"staunstrup" <jks@i4.auc.dk> wrote in message news:3f965964$0$54790$edfadb0f@dread11.news.tele.dk...
|
| > I vaguely remember some magazine's shoot-out between frame materials. I think the biking mag did
| > exactly what you are suggesting (ie, built
bikes
| > with similar geometry and size out of different metals). Darned if I
can
| > recall the results though. Maybe someone else here can remember the details.
| >
| >
| > Jean
| >
|
|
| In 'RoadBike Action', May 1995, Vol. 3, Nr. 5, p. 12-31, ISSN 1069-2648, 'The Ultimate Road Bike
| Shootout' was made with 5 'identical' bikes made
by
| a Harry Havnoonian in the different materials, steel, aluminium,
titanium,
| carbon fiber and metal matrix.
|
| ----
| Jan Kloster Staunstrup GIM-lab. Aalborg University, Denmark.
|
|

The shoot-out you cite sounds familiar (especially Havnoonian building the frames). So what were the
results of the test?

Jean