(Rik O'Shea) wrote in message . com...
(Carl Fogel) wrote in message . com...
Dear Rik,
I think that the original question was whether
these carbon Columbus Muscle Forks "break easily,"
not whether carbon forks in general last a long
time as long as you don't break them in a crash.
That is, what happens if you pop a pair of these
Columbus Muscle Forks in a vise and whack 'em with
a hammer to simulate a crash or wiggle 'em to mimic
ordinary riding stresses? Do the Columbus forks
bust more easily than other brands of carbon forks
or any kind of metal forks?
Like Dave, I appreciate your feedback, which suggests
that carbon forks in general survive ordinary riding
(but don't crash). That may be what Dave wanted to
know, but he might have been wondering if these Columbus
Muscles forks are the Ford Pinto of the carbon fork world,
too thin, too fragile, or somehow badly designed.
Carl Fogel
The following is from http://www.framebuilding.com/carbon%20forks.htm
although I dont specifically know how it compares to the testing
performed on carbon forks from other manufactures. ASTM standards call
for a load of 170 lbs. applied perpendicular to the steering axis,
both pushing and pulling for 50,000 cycles without failure. The
information below seems to suggest that the Columbus forks exceed
this.
-----------0---------
Columbus carbon forks are produced in accordance with ISO 9000. All
forks are marked and their history can be traced. The tests include
destruction testing and are performed on finished product samples.
They are very seve
* Frontal and side strength test:
A load of 200 N is first applied to the frontal part and then to
the side part of the fork. The flex is measured on each occasion and
this must not exceed a set value.
* Shock Test:
A mass of 250 N is dropped from a height of 430mm on a properly
restrained fork. In order to pass the test the fork must resist
without breakage or residual deformation.
* Static Test:
A load of 200 N is applied to the frontal part for 1 minute. In
order to pass the test the fork must resist without breakage or
deformation.
* Fatigue Test:
During this test an alternate force of +-600 N is applied. In
order to pass this test the fork must resist for 150,000 cycles
without breaking.
Dear Rik,
The site that you found seems to be the Columbus
Carbon parts web site:
http://www.framebuilding.com/carbon%20forks.htm
I found it fascinatinng. I'm ignorant about forks
and materials, but I'm wary of what seems like
confused marketing hype:
"Carbon fibre as a material is 4 times more resistant than steel and 8
times more resistant than aluminium. Its versatility and
directionality allows Columbus designers to modulate the section and
form of the fork blades to satisfy all design criteria, without
compromise or limitation. The Columbus composite fork blades have been
realized by overlapping 15 layers of T-700 aerospace carbon fibre and
then covering this externally with a layer of High Modulus Carbon
fibre, which is 20% lighter and 10% more resistant than T-700.
Additionally the full carbon fork, MUSCLE, also includes a special
reticular fabric in titanium called 'Ti Mesh titanium net'. This has a
considerable damping effect on high frequency vibrations within the
fork, such as those produced by irregular ground surfaces. Super
Muscle includes Kevlar and Nickel for improved weight saving while
maintaining strength and shock resistance."
What do they mean by "resistant"? Strength in
compression?
Why use 15 inner layers of inferior T-700 and
only one outer layer of the good stuff, which
is "20% lighter and 10% more resistant"?
(It sounds as if they could use the good stuff
and make a 10% stronger fork that would be 20%
lighter.)
Why does a carbon fork, often claimed to damp
vibration better than metal, need a layer of
metal mesh to damp vibrations?
How does including Kevlar and nickel in the
Super Muscle Fork save weight while maintaining
strength? Isn't nickel a denser and weaker metal
than the titanium used in the plain muscle fork?
(The titanium in the plain Muscle Fork has roughly
8 times nickel's yield strength and 33% more tensile
strength than nickel, a weaker metal that's twice as
dense as titanium--8,800 kg/cubic-meter versus 4,500
kg/cubic-meter:
http://www.simetric.co.uk/si_metals.htm
This density site also lists manure at 400
kg/cubic meter, a figure that may apply to
some of the Columbus site's explanations.)
Apart from such technical mysteries, it still
sounds as if we don't want to crash such forks,
which was the consensus of the experts in your
previous post. I've gathered elsewhere that
severe carbon damage can be invisible to the
naked eye, while metal tends to bend and reveal
its impending failure.
The ISO 9000 "shock test" mentioned on the site
sounds as if a 670-pound weight is dropped 17
inches onto an upright fork.
While surviving this thump sounds impressive,
ordinary BMX and mountain bikes routinely drop
250 pounds onto the front and rear from considerably
more than a foot and a half, so I'm not sure how
well this simulates a fork-damaging crash, which
typically involves the sideways force of ramming
something. Like a leg-bone, a fork resists impacts
from above that would easily break it from the side.
Again, I do appreciate the effort that you put into
finding this Columbus site, which certainly indicates
that the Muscle fork and its big brother both pass
the basic kinds of tests that I was wondering about
and that might be what the original poster wanted
to know--the ISO standard suggests that the Carbon
Muscle fork meets detailed fork standards, so it
ought to be fairly reliable, no matter what the
marketing people are babbling.
So thanks--it's awfully nice of you to cater to
my curiosity by finding that site.
Carl Fogel