Steel fork with carbon steerer?

Wayne Pein said:

I've got several bikes and feel that my bike with steel fork (84 Trek)
really soaks up the bumps. The fork flexes more than my carbon fork bike
(Kestrel).

Is is feasible for a manufacturer to produce a fork with steel blades
bonded to a carbon fiber steerer? The purpose of the carbon would be to
reduce the overall weight of the fork.

Wayne

I think they would be more likely to develop a completely carbon fork
that flexed to absorb bumps. How about decreasing your tire pressure or
trying one of the lighter carbon forks. The wound-up carbon fork has
really skinny legs and probably acts the way you want it to.

Wayne Pein said:

I've got several bikes and feel that my bike with steel fork (84
Trek) really soaks up the bumps. The fork flexes more than my
carbon fork bike (Kestrel).

I think this requires defining "soaking up bumps" and differentiating
that from absorbing vibration in the realm of one to two millimeters.
Fork rake on a bicycle is angled such that road roughness loads the
fork in compression, roughness in the range of bumps that matter to
durability. For this reason many forks are made with straight blades
that have an and angle that offsets the axle about 30mm forward of the
steer tube axis to reduce trail. Trail that would otherwise make
steering ungainly. For this purpose steel forks have curl at the end
that is for steering offset, not elasticity.

Because forks must not be loaded in bending from road shock,
suspension forks have about the same rake angle as rigid forks. In
contrast these can absorb bumps in the axis of the fork stanchions,
something a rigid fork does not do. To test of whether a steel fork
with a curl has springiness, a string can be tired from QR (axle) to
fork crown to prove that string will not go slack on bumps. Straight
forks angled at the crown make the results of this test obvious.

Quoted message said:

Is is feasible for a manufacturer to produce a fork with steel
blades bonded to a carbon fiber steerer? The purpose of the carbon
would be to reduce the overall weight of the fork.

What would benefit would the steel offer?

Jobst Brandt
[email hidden]

Wayne Pein said:

I've got several bikes and feel that my bike with steel fork (84
Trek) really soaks up the bumps. The fork flexes more than my
carbon fork bike (Kestrel).

I think this requires defining "soaking up bumps" and differentiating
that from absorbing vibration in the realm of one to two millimeters.
Fork rake on a bicycle is angled such that road roughness loads the
fork in compression, roughness in the range of bumps that matter to
durability. For this reason many forks are made with straight blades
that have an angle that offsets the axle about 30mm forward of the
steer tube axis to reduce trail. Trail that would otherwise make
steering ungainly. For this purpose steel forks have curl at the end
that is for steering offset, not elasticity.

Because forks must not be loaded in bending from road shock,
suspension forks have about the same rake angle as rigid forks. In
contrast these can absorb bumps in the axis of the fork stanchions,
something a rigid fork does not do. To test of whether a steel fork
with a curl has springiness, a string can be tired from QR (axle) to
fork crown to prove that string will not go slack on bumps. Straight
forks angled at the crown make the results of this test obvious.

Quoted message said:

Is is feasible for a manufacturer to produce a fork with steel
blades bonded to a carbon fiber steerer? The purpose of the carbon
would be to reduce the overall weight of the fork.

What benefit would steel offer?

Jobst Brandt
[email hidden]

Wayne Pein said:

I've got several bikes and feel that my bike with steel fork (84 Trek)
really soaks up the bumps. The fork flexes more than my carbon fork bike
(Kestrel).

Is is feasible for a manufacturer to produce a fork with steel blades
bonded to a carbon fiber steerer? The purpose of the carbon would be to
reduce the overall weight of the fork.

Certainly feasible, but given that the outside diameter of the steerer
tube was fixed back in the days when everything was steel, steel is
probably the best material for the job. It's certainly the stiffest for
a given OD, and steerer tubes do flex significantly. To use carbon the
tube walls would have to be quite thick to get adequate strength,
reducing a lot of the weight advantage. You can't perform the usual
trick of increasing the OD and reducing wall thickness to maintain
stiffness *and* strength.

Wayne Pein <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

I've got several bikes and feel that my bike with steel fork (84 Trek)
really soaks up the bumps. The fork flexes more than my carbon fork bike
(Kestrel).

Is is feasible for a manufacturer to produce a fork with steel blades
bonded to a carbon fiber steerer? The purpose of the carbon would be to
reduce the overall weight of the fork.

Not to say that what you "feel" is incorrect, but you might want to
look at this matter a little differently, that it is not an issue of
the materials used.

Rather than rewrite my earlier observations found in this group:
http://snipurl.com/907k

In my informal comparisons a Kestrel was at the harsh end of the ride
spectrum.
FWIW there were two charcteristics that changed noticeably among
forks, (1) ride softness and (2) steering quickness or precision.
However it was almost universal that (1) and (2) were inversely
proportional AND much of the difference in the feel of each fork could
be compensated for with a change in tire pressure of 10-15 psi.
Although ultimately I found greatest satisfaction in a "softer" fork
and firmer tires

DR

Quoted message said:

For this reason many forks are made with straight blades
that have an and angle that offsets the axle about 30mm forward of the
steer tube axis to reduce trail.

That amount of front axle offset is characteristic of a BMX bike with
20" wheels, though such bikes' forks get their offset from their
forward-mounted plate dropouts rather than any angle or bend in the
blades.

700c-wheeled bikes typically use fork offsets of 40 to 50mm, because
the amount of natural trail in a bicyle is proportional to wheel
diameter as well as head angle.

Chalo Colina

Quoted message said:

Fork rake on a bicycle is angled such that road roughness loads the
fork in compression,

Better double-check this hypothesis. I think that all forks are loaded
in flexure when riding over bumps (basically vertical loading unless
you are climbing curbs or logs) whether the fork blades are straight
or not. The angle of the steering axis from vertical and the offset of
the axle from the steering axis result in flexural stresses in the
fork due to vertical load. You need to draw some free body diagrams.
Simply resolve the vertical force at the axle into components parallel
and perpendicular to the steering axis, both components result in
flexural stresses in the blades of the fork.

The Kestrel fork is much stiffer in flexure than most carbon forks.
All carbon forks may be stiffer than steel

Quoted message said:

Quoted message said:

Is is feasible for a manufacturer to produce a fork with steel
blades bonded to a carbon fiber steerer? The purpose of the carbon
would be to reduce the overall weight of the fork.

What benefit would steel offer?

Steel is ductile which is nice in the event of failure and may not be
as stiff as some carbon forks.

Quoted message said:

Fork rake on a bicycle is angled such that road roughness loads the
fork in compression,

Better double-check this hypothesis. I think that all forks are loaded
in flexure when riding over bumps (basically vertical loading unless
you are climbing curbs or logs) whether the fork blades are straight
or not. The angle of the steering axis from vertical and the offset of
the axle from the steering axis result in flexural stresses in the
fork due to vertical load. You need to draw some free body diagrams.
Simply resolve the vertical force at the axle into components parallel
and perpendicular to the steering axis, both components result in
flexural stresses in the blades of the fork.

The Kestrel fork is much stiffer in flexure than most carbon forks.
All carbon forks may be stiffer than steel

Quoted message said:

Quoted message said:

Is is feasible for a manufacturer to produce a fork with steel
blades bonded to a carbon fiber steerer? The purpose of the carbon
would be to reduce the overall weight of the fork.

What benefit would steel offer?

Steel is ductile which is nice in the event of failure and may not be
as stiff as some carbon forks.

Quoted message said:

Fork rake on a bicycle is angled such that road roughness loads the
fork in compression,

Better double-check this hypothesis. I think that all forks are loaded
in flexure when riding over bumps (basically vertical loading unless
you are climbing curbs or logs) whether the fork blades are straight
or not. The angle of the steering axis from vertical and the offset of
the axle from the steering axis result in flexural stresses in the
fork due to vertical load. You need to draw some free body diagrams.
Simply resolve the vertical force at the axle into components parallel
and perpendicular to the steering axis, both components result in
flexural stresses in the blades of the fork.

The Kestrel fork is much stiffer in flexure than most carbon forks.
All carbon forks may be stiffer than steel

Quoted message said:

Quoted message said:

Is is feasible for a manufacturer to produce a fork with steel
blades bonded to a carbon fiber steerer? The purpose of the carbon
would be to reduce the overall weight of the fork.

What benefit would steel offer?

Steel is ductile which is nice in the event of failure and may not be
as stiff as some carbon forks.

anonymous chimed in:

Quoted message said:

Quoted message said:

Fork rake on a bicycle is angled such that road roughness loads the
fork in compression,

Quoted message said:

Better double-check this hypothesis. I think that all forks are
loaded in flexure when riding over bumps (basically vertical loading
unless you are climbing curbs or logs) whether the fork blades are
straight or not. The angle of the steering axis from vertical and
the offset of the axle from the steering axis result in flexural
stresses in the fork due to vertical load. You need to draw some
free body diagrams. Simply resolve the vertical force at the axle
into components parallel and perpendicular to the steering axis,
both components result in flexural stresses in the blades of the
fork.

The angle was chosen to be in-line with the statistically significant
distribution of road shock amplitude and frequency. Obviously a fork
is loaded in rearward bending during forceful braking and forward
bending while rolling on smooth surfaces. Fork fatigue failures that
I have seen were from forward bending (vertical moment about the fork
crown). This does not mean that significant road shocks are not
supported in axial compression by the fork, only that on smoother
roads that type of impact loading no longer rules in fork failures.

Quoted message said:

The Kestrel fork is much stiffer in flexure than most carbon forks.
All carbon forks may be stiffer than steel

So let's get back to the original contention... that one type of
(non-suspension) fork is more shock absorptive than another.

Quoted message said:

Quoted message said:

Quoted message said:

Is is feasible for a manufacturer to produce a fork with steel
blades bonded to a carbon fiber steerer? The purpose of the carbon
would be to reduce the overall weight of the fork.

Quoted message said:

Quoted message said:

What benefit would steel offer?

Quoted message said:

Steel is ductile which is nice in the event of failure and may not
be as stiff as some carbon forks.

Fatigue (steel) failures are not ductile although developing cracks
can be detected before failure. We can assume that the failures of
interest are not forced ruptures, or such failures would be common
early on when sprinting or braking.

Jobst Brandt
[email hidden]

Quoted message said:

The angle was chosen to be in-line with the statistically significant
distribution of road shock amplitude and frequency.

I guess you mean the angle of the steering axis from vertical. I will
admit that I don't know for certain why most bikes have about the same
angle. Although it is related to stability and handling - I think a
bike with a vertical axis would be stable enough to ride but I wonder
how it would handle. A really flat angle (chopper) can be hard to
handle. One of the problems about trying to understand the
engineering of bicycles is that they were not really developed by
engineering methods, as we know them today. A bicycle may still be
closer to a work of art than an engineered machine. Somewhat like the
steam engine, which was developed before the science/engineering of
thermodynamics existed - thermodynamics developed primarily in an
effort to explain why steam engines worked. Maybe we should formalize
the science/engineering of velomechanics.

The tilted steering axis does decrease the bending moment due to
braking in exchange for increasing the bending moment due to gravity
and vertical dynamic loading. All I am saying is that the bending
moment due to vertical loading is the primary mode of deformation in
the fork when talking about "soaking up the bumps" unless you have
axially soft forks (suspension forks). The forks are a cantilevered
beam and cantilevered beams deflect quite a bit. The axial deformation
of a solid fork is negligible.

The average rider probably cannot accurately assess the ride stiffness
of one modern fork in comparison to another. If the think their new
bike rides hard or soft it is more likely a change in rider position.
It is probably to subtle to subjectively evaluate.

Quoted message said:

Fork fatigue failures that
I have seen were from forward bending (vertical moment about the fork
crown).

Makes sense because it get so many more cycles of load.

Quoted message said:

So let's get back to the original contention... that one type of
(non-suspension) fork is more shock absorptive than another.

It is not possible to answer such a general question it will vary with
the geometry of the fork, steering angle, material stiffness, section
properties, etc. I simply believe that carbon fiber forks are
generally stiff in flexure and probably axially as well. They probably
tend to be over-strength due to brittleness. Any properly designed
fork will be some compromise between weight, strength, stiffness and
ease of fabrication (cost) - true of any engineered structure.

Quoted message said:

Quoted message said:

Quoted message said:

> Is is feasible for a manufacturer to produce a fork with steel
> blades bonded to a carbon fiber steerer?

Yes, it is possible and a nice fork might result but one must consider
weight, strength, stiffness and ease of fabrication. I guess I should
add fashion since we are talking about bicycles.

Quoted message said:

We can assume that the failures of
interest are not forced ruptures, or such failures would be common
early on when sprinting or braking.

Brittle failure has to be more catastrophic than ductile failure
regardless of the cause. If I happen to run head-on into an obstacle,
I want the fork to absorb as much energy as possible before it
separates from the bike. The same goes for when a stick gets poked
through the spokes.

Quoted message said:

The angle was chosen to be in-line with the statistically significant
distribution of road shock amplitude and frequency.

I guess you mean the angle of the steering axis from vertical. I will
admit that I don't know for certain why most bikes have about the same
angle. Although it is related to stability and handling - I think a
bike with a vertical axis would be stable enough to ride but I wonder
how it would handle. A really flat angle (chopper) can be hard to
handle. One of the problems about trying to understand the
engineering of bicycles is that they were not really developed by
engineering methods, as we know them today. A bicycle may still be
closer to a work of art than an engineered machine. Somewhat like the
steam engine, which was developed before the science/engineering of
thermodynamics existed - thermodynamics developed primarily in an
effort to explain why steam engines worked. Maybe we should formalize
the science/engineering of velomechanics.

The tilted steering axis does decrease the bending moment due to
braking in exchange for increasing the bending moment due to gravity
and vertical dynamic loading. All I am saying is that the bending
moment due to vertical loading is the primary mode of deformation in
the fork when talking about "soaking up the bumps" unless you have
axially soft forks (suspension forks). The forks are a cantilevered
beam and cantilevered beams deflect quite a bit. The axial deformation
of a solid fork is negligible.

The average rider probably cannot accurately assess the ride stiffness
of one modern fork in comparison to another. If the think their new
bike rides hard or soft it is more likely a change in rider position.
It is probably to subtle to subjectively evaluate.

Quoted message said:

Fork fatigue failures that
I have seen were from forward bending (vertical moment about the fork
crown).

Makes sense because it get so many more cycles of load.

Quoted message said:

So let's get back to the original contention... that one type of
(non-suspension) fork is more shock absorptive than another.

It is not possible to answer such a general question it will vary with
the geometry of the fork, steering angle, material stiffness, section
properties, etc. I simply believe that carbon fiber forks are
generally stiff in flexure and probably axially as well. They probably
tend to be over-strength due to brittleness. Any properly designed
fork will be some compromise between weight, strength, stiffness and
ease of fabrication (cost) - true of any engineered structure.

Quoted message said:

Quoted message said:

Quoted message said:

> Is is feasible for a manufacturer to produce a fork with steel
> blades bonded to a carbon fiber steerer?

Yes, it is possible and a nice fork might result but one must consider
weight, strength, stiffness and ease of fabrication. I guess I should
add fashion since we are talking about bicycles.

Quoted message said:

We can assume that the failures of
interest are not forced ruptures, or such failures would be common
early on when sprinting or braking.

Brittle failure has to be more catastrophic than ductile failure
regardless of the cause. If I happen to run head-on into an obstacle,
I want the fork to absorb as much energy as possible before it
separates from the bike. The same goes for when a stick gets poked
through the spokes.

Wayne Pein said:

I've got several bikes and feel that my bike with steel fork (84 Trek)
really soaks up the bumps.

Great bike!

Quoted message said:

The fork flexes more than my carbon fork bike
(Kestrel).

Are you sure it's the fork? Measurements show the Kestrel is about the
same stiffness as most steel forks (front to back), and more flexible
(side to side). See
http://www.sheldonbrown.com/rinard/rinard_forktest.html

My guess is it's probably something else that makes your Trek more
comfortable.

<Snip for brevity>
The average rider probably cannot accurately assess the ride stiffness

Quoted message said:

of one modern fork in comparison to another. If the think their new
bike rides hard or soft it is more likely a change in rider position.
It is probably to subtle to subjectively evaluate.

How is it that you can take one fork off, replace it with another fork same
rake, etc. but different material and notice a difference? I'm sure its not all
in your head.

My Kinesis Carbon D fork was way flexy. While sprinting I could watch the fork
tips moving back and forth in about a 1cm arc. Made me sell that fork it scared
me so much. I bought a Time carbon fork of the same rake, etc. Nothing else
changed, but the front end of the bike was MUCH stiffer.

Is it in my head? Don't think so.

M

"SDMike" <[email hidden]> wrote in message
news😄Co1d.265054$sh.121280@fed1read06...

Quoted message said:

<Snip for brevity>
The average rider probably cannot accurately assess the ride

stiffness

Quoted message said:

Quoted message said:

of one modern fork in comparison to another. If the think

their new

Quoted message said:

Quoted message said:

bike rides hard or soft it is more likely a change in rider

position.

Quoted message said:

Quoted message said:

It is probably to subtle to subjectively evaluate.

How is it that you can take one fork off, replace it with

another fork same

Quoted message said:

rake, etc. but different material and notice a difference? I'm

sure its not all

Quoted message said:

in your head.

My Kinesis Carbon D fork was way flexy. While sprinting I

could watch the fork

Quoted message said:

tips moving back and forth in about a 1cm arc. Made me sell

that fork it scared

Quoted message said:

me so much. I bought a Time carbon fork of the same rake, etc.

Nothing else

Quoted message said:

changed, but the front end of the bike was MUCH stiffer.

Is it in my head? Don't think so.

Absolutely not. I just installed my $79 pair of Nashbar carbon
forks with a 1" Al steerer, and they have quite notceable flex --
much more than the steel forks they replaced -- and more than my
old Kestrel EMS. I think they have too much lateral flex to use
on my racing bike, but they are perfectly fine for my commuter
bike. I went threadless on my ressurected 1979/80 Columbus SP
pigmobile (I used to race on this?) for under $125. Steel is
real (heavy), but adding a CF fork really lightens it up. -- Jay
Beattie.

"SDMike" <[email hidden]> wrote in message
news😄Co1d.265054$sh.121280@fed1read06...

Quoted message said:

<Snip for brevity>
The average rider probably cannot accurately assess the ride

stiffness

Quoted message said:

Quoted message said:

of one modern fork in comparison to another. If the think

their new

Quoted message said:

Quoted message said:

bike rides hard or soft it is more likely a change in rider

position.

Quoted message said:

Quoted message said:

It is probably to subtle to subjectively evaluate.

How is it that you can take one fork off, replace it with

another fork same

Quoted message said:

rake, etc. but different material and notice a difference? I'm

sure its not all

Quoted message said:

in your head.

My Kinesis Carbon D fork was way flexy. While sprinting I

could watch the fork

Quoted message said:

tips moving back and forth in about a 1cm arc. Made me sell

that fork it scared

Quoted message said:

me so much. I bought a Time carbon fork of the same rake, etc.

Nothing else

Quoted message said:

changed, but the front end of the bike was MUCH stiffer.

Is it in my head? Don't think so.

Absolutely not. I just installed my $79 pair of Nashbar carbon
forks with a 1" Al steerer, and they have quite notceable flex --
much more than the steel forks they replaced -- and more than my
old Kestrel EMS. I think they have too much lateral flex to use
on my racing bike, but they are perfectly fine for my commuter
bike. I went threadless on my ressurected 1979/80 Columbus SP
pigmobile (I used to race on this?) for under $125. Steel is
real (heavy), but adding a CF fork really lightens it up. -- Jay
Beattie.

"SDMike" <[email hidden]> wrote in message news:<DCo1d.265054$sh.121280@fed1read06>...

Quoted message said:

<Snip for brevity>
The average rider probably cannot accurately assess the ride stiffness

Quoted message said:

of one modern fork in comparison to another. If the think their new
bike rides hard or soft it is more likely a change in rider position.
It is probably to subtle to subjectively evaluate.

No it isn't too subtle to evaluate and I would guess it would be very
obvious to any rider who had the opportunity to try different forks on
the same bike. And simply changing a fork does not change the postion
of the rider.

Quoted message said:

How is it that you can take one fork off, replace it with another
fork same rake, etc. but different material and notice a difference?
I'm sure its not all in your head.

Agreed

Quoted message said:

My Kinesis Carbon D fork was way flexy. While sprinting
I could watch the fork tips moving back and forth in about a 1cm arc.

Yes, the variation in visible motion can be quite clear.

Quoted message said:

Made me sell that fork it scared me so much.
I bought a Time carbon fork of the same rake, etc. Nothing else
changed, but the front end of the bike was MUCH stiffer.

I also found a Time fork to be very stiff, but I did NOT like it just
for that reason.

Quoted message said:

Is it in my head? Don't think so.

No, not in your head, but not necessarily in the material either.
Weren't both of these forks carbon? The point being that different
forks can behave and feel different but the discernable difference is
not predictable based upon material alone as your own observations
demonstrate.

DR

Quoted message said:

How is it that you can take one fork off, replace it with another fork same
rake, etc. but different material and notice a difference? I'm sure its not
all in your head.

I think you can if the wheels, tire pressure, etc. are the same. I was
referring to a rider switching bikes.