CHOOSING A FORK

jim beam said:

Qui si parla Campagnolo said:

John Forrest Tomlinson said:

On 20 Mar 2006 05:37:31 -0800, "Qui si parla Campagnolo"
<[email hidden]> wrote:

>That would be true is the carbon fork were in the vicinity of the
>weight of a steel fork BUT like handlebars, they have dropped to the 10
>ounce range and all carbon and in an impact, this carbon is not safer
>than a 1.3 pound steel fork. One will bend, the other will break.

The only time I damaged a fork it was steel and I was going to hit the
ground regardless. And I saw a friends carbon fork snap both blades --
he was going to crash hard regardless of what happend to his bike.

Why do you think that, in a crash severe enough to bend a steel fork,
the fork breaking more dangerous than bending?

JT

Well, not hard to imagine say hitting a curb, where the steel fork
bends lots compared to both legs or the steerer breaking off of the
carbon fork, which would be more severe.

Steel does everything fork-wise that carbon does.

except load test 3x that of steel - for a reynolds fork at any rate. i
call that a significant difference. don't get me wrong, steel forks can
be beautiful and very reliable, but stronger in static load, they ain't,
stronger in fatigue, they ain't, and they /do/ attenuate some road buzz.
so, imo, carbon wins.

Quoted message said:

the 1 pound+- weight
savings means not much on a 180 pound rider and a 18 pound bike. But
carbon works fine, is very whizbang, impresses the ladies and the other
riders at the coffee shop on Sunday morning. But it is not a
significant improvement over a well made steel fork.

Quoted message said:

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Once more this is 'implied' that it is somehow better and significant.
Much like '1 1/8inch is much stiffer', 'compact is much stiffer',
'outboard bearings are much stuffer', that implies the thing it is
compared to is somehow soft, flexy, unsafe somehow.

Load test 3x that of steel, implies that steel is a questionable
material for a fork. it isn't, hasn't been for decades, centuries and
continues to be a great material, better than carbon in a lot of cases.
Looks, ride quality, repairability all trump carbon most of the time.

jim beam wrote:
---snip---

Quoted message said:

well, the reynolds load testing graph had the carbon fork breaking at
about 3x the load of the steel fork. call me old fashioned, but i'd say
that makes the carbon a better deal than the steel.

---more snipping---

Perhaps I'm oversimplifying, but wouldn't static load only come into
play if you were capable of putting that kind of load on the fork? It
seems to me that the argument you're making is akin to claiming that a
steel I-beam can support a far greater static load than a wooden 2x4,
and therefore everyone should build their homes with steel I-beams.

SYJ

jim beam said:

Qui si parla Campagnolo said:

Steel does everything fork-wise that carbon does.

except load test 3x that of steel - for a reynolds fork at any rate. i
call that a significant difference. don't get me wrong, steel forks can
be beautiful and very reliable, but stronger in static load, they ain't,

But if you exceed the static strength of a steel fork with a transient
load, you have a slightly bent fork. Exceed the strength of a
carbon-plastic fork with a transient load, and you're surfing pavement
on your face.

I've wasted literally dozens of steel forks, only one of which snapped
off (at the steerer threads). Would I be willing to bet my face that
none of them saw a a peak of 3X their yield stress? Not for a moment.

Chalo

Qui si parla Campagnolo said:

Steel does everything fork-wise that carbon does. the 1 pound+- weight
savings means not much on a 180 pound rider and a 18 pound bike. But
carbon works fine, is very whizbang, impresses the ladies and the other
riders at the coffee shop on Sunday morning.

Almost anyone with a decent income who wants it can have carbon these
days, so there's no cachet in it anymore. The Cult Of Steel seems to be
much more fervid, aggressive and paranoid.

And if you want to pick up chicks, you've picked the wrong hobby unless
you ride /really/ slowly, regardless of your bike :-)

--
Home page: http://members.westnet.com.au/mvw

Chalo said:

if you exceed the static strength of a steel fork with a transient
load, you have a slightly bent fork.

Can this happen in situations where the rider isn't going to crash
anyway? For a peson of "normal" weight (I know you and I think the OP
are way outside the norm.) It seems to me that the rider is probably
hitting a high curb or a wall or something and headed over the bars
anyway.

JT

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jim beam said:

well, the reynolds load testing graph had the carbon fork breaking at
about 3x the load of the steel fork. call me old fashioned, but i'd say
that makes the carbon a better deal than the steel.

Quoted message said:

A 'better deal', sorry, don't see it. Have you often broken or bent
steel forks? And see the need to have a safer fork?

Same old saw, quill stems, 1 inch hs, square taper...all 'need' to be
replaced...for safety. Hardly, for marketing. I'm certainly not
surprised reynolds touts the 3x type thing. Giant said how much
stuiffer, lighter, more comfy(huh?) a compact frame was. How much
better a threadless fork was by Diacomp...all that is not as
black/white as it implies. If ya like a carbon fork, rationalize it any
way you wish, I have ridden steel forks for 2 decades and will
continue. Have never bent or broken one, in spite of my .1 offa ton
weight.

Chalo said:

jim beam said:

Qui si parla Campagnolo said:

Steel does everything fork-wise that carbon does.

except load test 3x that of steel - for a reynolds fork at any rate. i
call that a significant difference. don't get me wrong, steel forks can
be beautiful and very reliable, but stronger in static load, they ain't,

But if you exceed the static strength of a steel fork with a transient
load, you have a slightly bent fork. Exceed the strength of a
carbon-plastic fork with a transient load, and you're surfing pavement
on your face.

I've wasted literally dozens of steel forks, only one of which snapped
off (at the steerer threads). Would I be willing to bet my face that
none of them saw a a peak of 3X their yield stress? Not for a moment.

Chalo

Which I guess begs a question for me anyway, what type of fatigue and or
failure data is available from the manufacturers of these forks like
look or easton or someone well invested in CF technology. Is there a
standard to be followed or can they (the OEM's) due whatever they feel
is right and "reasonable". I can't image tons of money being invested
into the process without having some reasonable guidelines or specs.

Quoted message said:

Chalo said:

jim beam said:

Qui si parla Campagnolo wrote:
> Steel does everything fork-wise that carbon does.
except load test 3x that of steel - for a reynolds fork at any
rate. i call that a significant difference. don't get me wrong,
steel forks can be beautiful and very reliable, but stronger in
static load, they ain't,

But if you exceed the static strength of a steel fork with a
transient load, you have a slightly bent fork. Exceed the strength
of a carbon-plastic fork with a transient load, and you're surfing
pavement on your face.

Or, if while using a carbon fork, you exceed the steel fork's strength
limit, you have still about two-thirds of the strength limit of the carbon
fork before reaching its potential failure point. If at 101% of steel's
strength, steel bends, and somewhere around (just guessing) 150%, it breaks
in pieces, then the carbon fork is still not at half its strength limit. No
drama.

Corollary : if carbon forks need to be able to survive shocks that steel
forks can survive, carbon forks are just fine, and better. I assumed you
thought that 3X is OK as the carbon limit, according to miniscule's figures.
--
Bonne route !

Sandy
Verneuil-sur-Seine FR

Sandy said:

Quoted message said:

Quoted message said:

But if you exceed the static strength of a steel fork with a
transient load, you have a slightly bent fork. Exceed the strength
of a carbon-plastic fork with a transient load, and you're surfing
pavement on your face.

If at 101% of steel's
strength, steel bends, and somewhere around (just guessing) 150%, it breaks
in pieces, then the carbon fork is still not at half its strength limit.

You don't fully understand what you're talking about. Steel, as it
yields, absorbs energy. The force that caused it to yield has only so
much energy behind it, and the amount of energy (delivered at a force
that exceeds the steel's yield stress) is what would cause a steel fork
to fold, break off, etc. If you use the back of a teaspoon to whack
the leg of your steel fork hard enough to leave a mark on the metal,
you have surpassed its yield stress locally-- but you have not applied
enough energy to cause any significant damage.

Moreover, once the yield stress of a steel fork has been surpassed
(that is, once it has become bent), the metal is stronger than it was
before, since it has been cold worked. So to bend the fork some more,
you not only have to come up with some more energy, but you have to
push it a little harder than before to get the metal to yield further.

A carbon-plastic fork displays, ironically, almost no plastic
deformation. Once the yield stress has been surpassed in some part of
the fork, structural fibers break and the material becomes weaker in
proportion to the number of fibers that have been severed. If those
fibers are among the most highly stressed in the fork, like say *the
ones on the outside surface of the fork*, then the scene is set for a
cascading failure that takes a lot of force, but very little energy, to
set in motion.

An extreme of the strength-without-toughness quality I describe is
embodied by ordinary glass, which in its yield stress is often stronger
than steel (sometimes many times stronger). However, the "ordeal of
the teaspoon" that I described above would easily destroy a glass fork
that was built to the same hypothetical yield strength as a steel fork.
Glass has extremely low toughness. CFRPs that are used in bicycles
are much tougher than glass, but not nearly as tough as any structural
metal (let alone steel, which is one of the toughest).

There are a lot of factors that weigh in to the damage tolerance of a
CFRP, such as fiber density, toughness of the matrix resin, fabric
weave and layup, etc. But generally speaking, the more rigid and the
higher the strength-to-weight ratio of a CFRP, the less toughness it
will display and the more suddenly it is apt to fail.

If you were given an average steel-framed bike, an average
carbon-framed bike, and a two-by-four to beat on them with, and you
were instructed to flail them until some part of the frame of each one
was broken completely through, which one do you think would require
more work on your part? You could probably take out the carbon-plastic
frame with one well-placed blow, but it's possible that you'd be unable
to sever any part of the steel frame at all before either your strength
or the two-by-four gave out. In a test fixture, the carbon-plastic
frame would almost certainly prove itself to be the "stronger" of the
two (if you did the test before breaking the frame, of course). But
the toughness of the steel bike is what allows it to hang together
after its limits have been exceeded.

Chalo Colina

mrbubl said:

what type of fatigue and or
failure data is available from the manufacturers of these forks like
look or easton or someone well invested in CF technology. Is there a
standard to be followed or can they (the OEM's) due whatever they feel
is right and "reasonable". I can't image tons of money being invested
into the process without having some reasonable guidelines or specs.

First off, CFRPs don't "fatigue" in the sense that metals do. Simply
put, metal fatigue is the process by which the microscopic flaws in all
metal grow into microscopic cracks (and then into macroscopic cracks)
as repeated loads are applied. These loads need not be in excess of
the metal's yield stress at any point in the structure.

CFRP is not subject to crack propagation from microscopic flaws. If
the fibers remain intact, they are as strong as they ever were. The
plastic matrix can degrade, but this is more likely to be a result of
age or exposure than of cyclical stress.

I am certain that manufacturers of CFRP consumer products just design
their products with an especially generous safety factor-- basically a
multiple of the forces they expect the product to see in service. In
my industrial experience, a structural safety factor of 2.5X is typical
for items that present a risk of injury or serious property damage.
For bicycles, it might be more, since their operation environment is so
poorly controlled and the liability risk is so high. "jim beam"
referred to materials from Reynolds that suggested they may use a
structural safety factor equivalent to three times that of a normal
steel fork.

Chalo Colina

In article <[email hidden]>,

Sandy said:

Quoted message said:

Chalo said:

jim beam wrote:
> Qui si parla Campagnolo wrote:
>> Steel does everything fork-wise that carbon does.
> except load test 3x that of steel - for a reynolds fork at any
> rate. i call that a significant difference. don't get me wrong,
> steel forks can be beautiful and very reliable, but stronger in
> static load, they ain't,

But if you exceed the static strength of a steel fork with a
transient load, you have a slightly bent fork. Exceed the strength
of a carbon-plastic fork with a transient load, and you're surfing
pavement on your face.

Or, if while using a carbon fork, you exceed the steel fork's strength
limit, you have still about two-thirds of the strength limit of the carbon
fork before reaching its potential failure point. If at 101% of steel's
strength, steel bends, and somewhere around (just guessing) 150%, it breaks
in pieces, then the carbon fork is still not at half its strength limit. No
drama.

On single impact an intact steel fork does no break `in
pieces'.

At these force levels material properties are immaterial
to the rider hitting the road.

The main discussion is the failure modes of carbon forks
and steel forks, hidden damage, and the relative frequency
that the failure mode makes a difference.

You are following the trail left by jim beam's red
herring.

Quoted message said:

Corollary : if carbon forks need to be able to survive shocks that steel
forks can survive, carbon forks are just fine, and better. I assumed you
thought that 3X is OK as the carbon limit, according to miniscule's figures.

--
Michael Press

Dans le message de
news:[email hidden],
Chalo <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Sandy said:

Quoted message said:

> But if you exceed the static strength of a steel fork with a
> transient load, you have a slightly bent fork. Exceed the strength
> of a carbon-plastic fork with a transient load, and you're surfing
> pavement on your face.

If at 101% of steel's
strength, steel bends, and somewhere around (just guessing) 150%, it
breaks in pieces, then the carbon fork is still not at half its
strength limit.

You don't fully understand what you're talking about.

Easy for _you_ to say ; actually, for anyone to say 🙂

Quoted message said:

Steel, as it
yields, absorbs energy. The force that caused it to yield has only so
much energy behind it, and the amount of energy (delivered at a force
that exceeds the steel's yield stress) is what would cause a steel
fork to fold, break off, etc. If you use the back of a teaspoon to
whack the leg of your steel fork hard enough to leave a mark on the
metal, you have surpassed its yield stress locally-- but you have not
applied enough energy to cause any significant damage.

Moreover, once the yield stress of a steel fork has been surpassed
(that is, once it has become bent), the metal is stronger than it was
before, since it has been cold worked. So to bend the fork some more,
you not only have to come up with some more energy, but you have to
push it a little harder than before to get the metal to yield further.

A carbon-plastic fork displays, ironically, almost no plastic
deformation. Once the yield stress has been surpassed in some part of
the fork, structural fibers break and the material becomes weaker in
proportion to the number of fibers that have been severed. If those
fibers are among the most highly stressed in the fork, like say *the
ones on the outside surface of the fork*, then the scene is set for a
cascading failure that takes a lot of force, but very little energy,
to set in motion.

An extreme of the strength-without-toughness quality I describe is
embodied by ordinary glass, which in its yield stress is often
stronger than steel (sometimes many times stronger). However, the
"ordeal of the teaspoon" that I described above would easily destroy
a glass fork that was built to the same hypothetical yield strength
as a steel fork. Glass has extremely low toughness. CFRPs that are
used in bicycles are much tougher than glass, but not nearly as tough
as any structural metal (let alone steel, which is one of the
toughest).

There are a lot of factors that weigh in to the damage tolerance of a
CFRP, such as fiber density, toughness of the matrix resin, fabric
weave and layup, etc. But generally speaking, the more rigid and the
higher the strength-to-weight ratio of a CFRP, the less toughness it
will display and the more suddenly it is apt to fail.

If you were given an average steel-framed bike, an average
carbon-framed bike, and a two-by-four to beat on them with, and you
were instructed to flail them until some part of the frame of each one
was broken completely through, which one do you think would require
more work on your part? You could probably take out the
carbon-plastic frame with one well-placed blow, but it's possible
that you'd be unable to sever any part of the steel frame at all
before either your strength or the two-by-four gave out. In a test
fixture, the carbon-plastic frame would almost certainly prove itself
to be the "stronger" of the two (if you did the test before breaking
the frame, of course). But the toughness of the steel bike is what
allows it to hang together after its limits have been exceeded.

Chalo Colina

I'll take you on your word. Interesting. Thanks.
--
Sandy
Verneuil-sur-Seine
*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

John Forrest Tomlinson said:

Chalo said:

if you exceed the static strength of a steel fork with a transient
load, you have a slightly bent fork.

Can this happen in situations where the rider isn't going to crash
anyway? For a peson of "normal" weight (I know you and I think the OP
are way outside the norm.) It seems to me that the rider is probably
hitting a high curb or a wall or something and headed over the bars
anyway.

It happens all the time. You might have done it yourself when you were
a kid.

For riders of ordinary size or smaller, a transient fork overload that
doesn't cause a crash is usually the result of landing from a jump.
This is what's happened to bikes you see that have the forks bent
_forwards_.

The transient overloads I have had were almost all resulting from
zealous application of the brakes. This bends the forks backwards much
in the same way as a frontal impact. I had a couple of forks bend
backwards at the cantilever bosses rather than at the fork crown.

Chalo Colina

Chalo said:

John Forrest Tomlinson said:

Chalo said:

if you exceed the static strength of a steel fork with a transient
load, you have a slightly bent fork.

Can this happen in situations where the rider isn't going to crash
anyway? For a peson of "normal" weight (I know you and I think the OP
are way outside the norm.) It seems to me that the rider is probably
hitting a high curb or a wall or something and headed over the bars
anyway.

It happens all the time.

Quoted message said:

You might have done it yourself when you were
a kid.

Hard enough to bend a fork? No.

Quoted message said:

For riders of ordinary size or smaller, a transient fork overload that
doesn't cause a crash is usually the result of landing from a jump.
This is what's happened to bikes you see that have the forks bent
_forwards_.

How many people jump road bikes?

JT

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Michael Warner said:

And if you want to pick up chicks, you've picked the wrong hobby unless
you ride /really/ slowly, regardless of your bike :-)

Duhhh! That's what the Xtracycle is for!

;-)

OT: Good sigmonster.

--
Dane Buson - [email hidden]
"As an adolescent I aspired to lasting fame, I craved factual certainty,
and I thirsted for a meaningful vision of human life -- so I became a
scientist. This is like becoming an archbishop so you can meet girls."
-- Matt Cartmill

John Forrest Tomlinson said:

How many people jump road bikes?

Anybody who finds himself faced with a curb, pothole, broken bottle,
etc., while moving at too high a speed to avoid it. But you knew that.

Chalo

Chalo said:

John Forrest Tomlinson said:

How many people jump road bikes?

Anybody who finds himself faced with a curb, pothole, broken bottle,
etc., while moving at too high a speed to avoid it. But you knew that.

I've never seen a fork bent by that kind of thing and assumed you
meant something more severe than just going over a little thing like
that. I still just can't believe what you're describing -- jumping a
road bike bending the forks -- is common.

JT

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John Forrest Tomlinson said:

On 23 Mar 2006 17:12:46 -0800, "Chalo" <[email hidden]> wrote:
How many people jump road bikes?

I do, every day: to jump e.g. over branches on cycle tracks.

Gr, Derk

John Forrest Tomlinson said:

Chalo said:

John Forrest Tomlinson said:

Chalo wrote:

>if you exceed the static strength of a steel fork with a transient
>load, you have a slightly bent fork.

Can this happen in situations where the rider isn't going to crash
anyway? For a peson of "normal" weight (I know you and I think the OP
are way outside the norm.) It seems to me that the rider is probably
hitting a high curb or a wall or something and headed over the bars
anyway.

It happens all the time.

Quoted message said:

You might have done it yourself when you were
a kid.

Hard enough to bend a fork? No.

Quoted message said:

For riders of ordinary size or smaller, a transient fork overload that
doesn't cause a crash is usually the result of landing from a jump.
This is what's happened to bikes you see that have the forks bent
_forwards_.

How many people jump road bikes?

Mine occasionally sees a foot or more of air.

Quoted message said:

JT

***

Robin Hubert