Comparison of Auminium, Steel and Carbon forks?

Ben C? wrote:

[...]

Right. Three forks of the same make and model should be exactly
the same (although variance is likely to go up substantially at the
bottom end of the market), but you can't just test one carbon fork
next to one aluminum fork and say that the difference is the
material. Whatever vibration parameter you're measuring is going
to have a big enough range across different models of carbon forks
that it's going to overlap with the range across different models
of aluminum forks.

Sometimes different materials dictate a different shape.

For example, I think I'm right in saying that if you make an
aluminium fork as flexy as you can make a steel one the aluminium
one will fatigue badly. So you have to make it a bit thicker and/or
fatter and stiffer. Sure you _could_ make a fork just as stiff out
of steel, but you don't have to and might not.

So it's better to compare complete forks as sold and then say
something like "out of the 100 forks tested, the CF ones mostly
absorbed vibration better than the Al ones".

Not to overlook that traditional steel forks had weaker (thinner wall)
steertubes and that most fork flex arose there. This was most visible
by holding the brake locked while rocking the bicycle fore and aft.
This was borne out by the fretting head bearing dimples because most
of this "fork flex" caused the fork crown to rock fore and aft.
Springs are usually made of steel and for that reason other material
steer tubes will have different flexure response.

Beyond that assessment, perceived road shock is primarily the axial
component of vibration traveling to hen handlebars and this is less
affected by steertube or even fork blade flex. I think this
assessment of ride comfort is barking up the wrong tree, so to speak.

Jobst Brandt

Ben C wrote:
snip for clarity


I would expect there to be much more likely to be non-negligible
differences between forks.


of course. krygowski, being an intelligent, informed engineering
professor with access to the correct instrumentation, already the owner
of a cross-section of different forks, a sound knowledge of the
principles, and with an open, inquiring mind, has already tested this
position and is simply waiting for an opportunity to publish his
results. or he's simply an idiot voicing underinformed opinion as fact
and who has no inclination to actually test any damned thing that could
possibly upset his comfy luddite little world.

wrote:
Ben C? wrote:

[...]

Right. Three forks of the same make and model should be exactly
the same (although variance is likely to go up substantially at the
bottom end of the market), but you can't just test one carbon fork
next to one aluminum fork and say that the difference is the
material. Whatever vibration parameter you're measuring is going
to have a big enough range across different models of carbon forks
that it's going to overlap with the range across different models
of aluminum forks.

Sometimes different materials dictate a different shape.

For example, I think I'm right in saying that if you make an
aluminium fork as flexy as you can make a steel one the aluminium
one will fatigue badly. So you have to make it a bit thicker and/or
fatter and stiffer. Sure you _could_ make a fork just as stiff out
of steel, but you don't have to and might not.

So it's better to compare complete forks as sold and then say
something like "out of the 100 forks tested, the CF ones mostly
absorbed vibration better than the Al ones".

Not to overlook that traditional steel forks had weaker (thinner wall)
steertubes and that most fork flex arose there. This was most visible
by holding the brake locked while rocking the bicycle fore and aft.
This was borne out by the fretting head bearing dimples because most
of this "fork flex" caused the fork crown to rock fore and aft.
Springs are usually made of steel and for that reason other material
steer tubes will have different flexure response.

Beyond that assessment, perceived road shock is primarily the axial
component of vibration traveling to hen handlebars and this is less
affected by steertube or even fork blade flex. I think this
assessment of ride comfort is barking up the wrong tree, so to speak.

eh? is this the same famous jobst brandt that presumes that there is no
force associated with rim displacement of 0.003" - and that a rider
can't feel that force? the same famous jobst brandt that thinks bike
bearings are hydrodynamically separated? the jobst brandt that thinks
bearings can't true brinell? and you're now trying to tell us that you
can tell the difference between different materials in steer tubes, but
fork blade material doesn't count?

On Apr 19, 11:05*am, Dan O wrote:
On Apr 19, 6:48 am, Mike Rocket J Squirrel





wrote:
On 4/19/2008 6:31 AM wrote:

On Fri, 18 Apr 2008 13:58:51 -0800, agcou wrote:

On Thu, 17 Apr 2008 19:55:23 -0400, wrote:

On Thu, 17 Apr 2008 15:23:53 -0700 (PDT), blackhead
wrote:

Are there any impartial tests that have been done on Auminium, Steel
and Carbon forks? Some people say carbon absorbs vibration better than
steel and Aluminium, others say it makes little difference... etc etc
The differences of design, materials quality and manufacture are greater than
the differences in the materials themselves. *Even in weight there is an
intersection between the three. I've got bikes with all three and they've all
got something going for them.

Really depends on what you're doing with the bike and which forks you're
choosing from.
Did you read the OP's question?

Yeah, there are no impartial tests that establish the relative characteristics
of forks made from different materials. Such a test would have to hold all other
variables constant in a way that simply isn't possible.

How come? Not arguing, just curious. Seems (to me, not a mechanical
engineer nor wrench) that one could get three forks with same geometry,
tilt at proper head tube angle, clamp dropouts to shaker table, add mass
loading from above, hang some accelerometers on the stem and let 'er rip..
Just to see, y'know?

I've only ever ridden steel (and some of that plenty cheesy), but it
seems to me the problem with this kind of test is that the chosen
"geometry, tilt, load, etc." - not to mention thickness, etc. - might
favor one material over another, and may or may not be suitable
parameters for a given bike, rider, and purpose. *And then the matter
of translating measured results into characteristics favorable for
riding on... And then it also occurs to me that a shaker table is
quite a different thing than a bicycle wheel.

This kind of testing might be okay for a big manufacturer's R&D
(although there goes "impartial" out the window if the marketing dept
has any influence ;-), but for choosing what to ride on, the proof is
(always) in the pudding.- Hide quoted text -


I have had steel, aluminum and CF forks all on the same 20+ year old
Cannondale frame. There was a suprisingly minor difference between
the original steel forks and the replacement 90's Kestrel CF (steel
steerer) -- except weight. Both were very stiff. I also had a pair
of aluminum forks on the bike for a short while. They were from a
later Cannondale 2.8 and were quite spongy climbing out of the
saddle. The 2.8 frame broke, and eventually I got a free replacement
frame with OEM carbon forks that were also stiffer than the original
aluminum forks . I have never found that carbon forks were magical in
terms of absorbing vibration. I have never owned a pair with a carbon
steerer, though, which may have additional magicality.-- Jay Beattie.

In article , says...
On 18 Apr, 00:55, wrote:
On Thu, 17 Apr 2008 15:23:53 -0700 (PDT), blackhead
wrote:

Are there any impartial tests that have been done on Auminium, Steel
and Carbon forks? Some people say carbon absorbs vibration better than
steel and Aluminium, others say it makes little difference... etc etc

The differences of design, materials quality and manufacture are greater than
the differences in the materials themselves. *Even in weight there is an
intersection between the three. I've got bikes with all three and they've all
got something going for them.

Really depends on what you're doing with the bike and which forks you're
choosing from.

So do Carbon forks really absorb vibration significantly better than
Aluminium, so giving a better ride?

Hmmm, my carbon-forks (attached to a carbon frame road bike - tyres at 110-115psi) don't do a hell of a lot of
absorbing when I ride over the coarse chip road surface that our wonderful city council decided to plaster all over my
commuting route, whereas my aluminiun forks (attached to a full-suspension mountain bike - 120 mm front travel) does a
fine job of absorbing all the bumps induced by fist-sized cobbles on a fast down-hill track. Can I make any conclusions
from this - only that the geometry, tyres, build and whatever is probably of far more significance.

To compare apples with apples, my CF road-bike is a lot lighter than th eold steel-frame, but I don't think there is a
_significant_ change in vibration absorption.

Mike

In article , says...
wrote:
On Apr 19, 10:18 am, Mike Rocket J Squirrel
Right. Three forks of the same make and model should be exactly the
same (although variance is likely to go up substantially at the bottom
end of the market), but you can't just test one carbon fork next to
one aluminum fork and say that the difference is the material.

but previously you were saying there would be "vastly different results"
- which of these conflicting statements would you have us believe?

This could be a result of wishful thinking of the form: " I spent vast amounts of hard-earned cash on these new forks,
so I had better be able to detect a vastly improved ride"...

Mike

On Apr 20, 3:10 pm, jim beam wrote:
Ben C wrote:

snip for clarity



I would expect there to be much more likely to be non-negligible
differences between forks.

of course. krygowski, being an intelligent, informed engineering
professor with access to the correct instrumentation, already the owner
of a cross-section of different forks, a sound knowledge of the
principles, and with an open, inquiring mind, has already tested this
position and is simply waiting for an opportunity to publish his
results. or he's simply an idiot voicing underinformed opinion as fact
and who has no inclination to actually test any damned thing that could
possibly upset his comfy luddite little world.

False dichotomy, jim. One doesn't have to personally run tests and
publish results to recognize the bull**** component of the advertising
hype that pops up in bike magazine ads and articles - things like
"rigid, yet compliant," "superfoods that increase healing power,"
"sealing gaps at the molecular level reduces friction at racing
speeds." Yes, and "incomparable, magic ride quality."

And a careful reader will note that I was simply giving my speculation
on what a fork comparison test would show. While I'd be willing to
bet with my friends on the issue, I wouldn't testify in court unless
I'd performed the proper test, or seen results I judged worthwhile.

Again, the worthwhile test would be a blind, on-road comparison test
using multiple riders, where the other factors were held constant.
It's the only way to filter out the placebo effect.

- Frank Krygowski

On Apr 20, 9:33 pm, Mike wrote:


Hmmm, my carbon-forks (attached to a carbon frame road bike - tyres at 110-115psi) don't do a hell of a lot of
absorbing when I ride over the coarse chip road surface...

I have two good friends who have bought the Specialized carbon frames
& forks with the "Zerts" inserts. Both say the bikes are nice for
their lightness; but neither feels they can detect any particular
vibration absorption.

- Frank Krygowski

wrote:
On Apr 20, 3:10 pm, jim beam wrote:
Ben C wrote:

snip for clarity



I would expect there to be much more likely to be non-negligible
differences between forks.
of course. krygowski, being an intelligent, informed engineering
professor with access to the correct instrumentation, already the owner
of a cross-section of different forks, a sound knowledge of the
principles, and with an open, inquiring mind, has already tested this
position and is simply waiting for an opportunity to publish his
results. or he's simply an idiot voicing underinformed opinion as fact
and who has no inclination to actually test any damned thing that could
possibly upset his comfy luddite little world.

False dichotomy, jim. One doesn't have to personally run tests and
publish results to recognize the bull**** component of the advertising
hype

a highly scholarly approach to any technological problem. not.



that pops up in bike magazine ads and articles - things like
"rigid, yet compliant," "superfoods that increase healing power,"
"sealing gaps at the molecular level reduces friction at racing
speeds." Yes, and "incomparable, magic ride quality."

And a careful reader will note that I was simply giving my speculation
on what a fork comparison test would show. While I'd be willing to
bet with my friends on the issue, I wouldn't testify in court unless
I'd performed the proper test, or seen results I judged worthwhile.

so again, you're prepared to pronounce judgment on a subject with which
you have no experience.



Again, the worthwhile test would be a blind, on-road comparison test
using multiple riders, where the other factors were held constant.
It's the only way to filter out the placebo effect.


you're a complete blathering idiot krygowski.

Mike wrote:
In article , says...
wrote:
On Apr 19, 10:18 am, Mike Rocket J Squirrel
Right. Three forks of the same make and model should be exactly the
same (although variance is likely to go up substantially at the bottom
end of the market), but you can't just test one carbon fork next to
one aluminum fork and say that the difference is the material.
but previously you were saying there would be "vastly different results"
- which of these conflicting statements would you have us believe?

This could be a result of wishful thinking of the form: " I spent vast amounts of hard-earned cash on these new forks,
so I had better be able to detect a vastly improved ride"...


so what happens when attenuation is still apparent with cheapo sub $100
carbon forks vs. expensiveo custom steel costing more than twice that
much then? would that be wishful thinking too? given that one of the
material properties of cfrp is that it does indeed attenuate vibration...