straight blade forks vs. raked fork



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T

Tedk618265

Guest
I am looking at getting a carbon fork for my aluminum road bike. What are the
advantages/disadvantages of a fork with straight blades over one with a conventional raked design?
 
K

Kbh

Guest
All forks have rake, even straight blade forks.

See:

http://www.sheldonbrown.com/gloss_r.html#rake

The only difference would be an imperceptibly greater stiffness in the straight bladed one.
Personally, I prefer the appearance of curved fork blades.

"TedK618265" <[email protected]> wrote in message
news:[email protected]...
> I am looking at getting a carbon fork for my aluminum road bike. What are
the
> advantages/disadvantages of a fork with straight blades over one with a conventional raked design?
 
P

Paul Southworth

Guest
In article <[email protected]>, TedK618265 <[email protected]> wrote:
>I am looking at getting a carbon fork for my aluminum road bike. What are the
>advantages/disadvantages of a fork with straight blades over one with a conventional raked design?

Approximately nothing assuming both have the same rake and construction. The curved ones look a lot
better though, that is the Lord's truth.

--Paul
 
D

David L. Johnso

Guest
On Sat, 01 Mar 2003 20:37:28 -0500, TedK618265 wrote:

> I am looking at getting a carbon fork for my aluminum road bike. What are the
> advantages/disadvantages of a fork with straight blades over one with a conventional raked design?

None either way. A straight-bladed fork is somewhat of a misnomer, since there is indeed the same
sort of "rake" as in a curved fork. The difference is that a straight-blade fork's blads come
straight from the crown at a slight forward angle to the headtube, while a curved-blade fork
achieves the same offset through the curve of the blades.

Both designs are rigid in the fork blades themselves, and all flex occurs with either design at the
crown itself.

Get whichever looks better to you.

--

David L. Johnson

__o | Become MicroSoft-free forever. Ask me how. _`\(,_ | (_)/ (_) |
 
D

Dave Lehnen

Guest
TedK618265 wrote:
> I am looking at getting a carbon fork for my aluminum road bike. What are the
> advantages/disadvantages of a fork with straight blades over one with a conventional raked design?

Not much either way. The bending and torsional (twisting) stiffness will be nearly identical, for
forks of similar construction. For loads directly up the fork, the straight-bladed fork will be
stiffer, since it is then loaded in pure compression, while the curved fork has bending loads
applied to it. Whether or not you could feel the difference is another question. You would be more
likely to feel the difference if you like to use very high tire pressures. The straight-bladed fork
could be lighter, but not by enough to matter. Both straight-bladed and curved forks offset the axle
from the steering axis, so both have rake in bicycle terminology. For either type, less rake gives
more trail which gives more stability, but slightly higher-effort steering. More importantly, all
straight-bladed forks are ugly, while most curved forks look good.<g>

Dave Lehnen
 
B

Boris Foelsch

Guest
If there's no difference, how come many cyclo-cross bike designs use straight forks?

Straight blades can be beautiful. Not all of them are.

Boris Foelsch

"Dave Lehnen" <[email protected]> wrote in message news:[email protected]...
> TedK618265 wrote:
> > I am looking at getting a carbon fork for my aluminum road bike. What
are the
> > advantages/disadvantages of a fork with straight blades over one with a conventional raked
> > design?
>
> Not much either way. The bending and torsional (twisting) stiffness will be nearly identical, for
> forks of similar construction. For loads directly up the fork, the straight-bladed fork will be
> stiffer, since it is then loaded in pure compression, while the curved fork has bending loads
> applied to it. Whether or not you could feel the difference is another question. You would be more
> likely to feel the difference if you like to use very high tire pressures. The straight-bladed
> fork could be lighter, but not by enough to matter. Both straight-bladed and curved forks offset
> the axle from the steering axis, so both have rake in bicycle terminology. For either type, less
> rake gives more trail which gives more stability, but slightly higher-effort steering. More
> importantly, all straight-bladed forks are ugly, while most curved forks look good.<g>
>
> Dave Lehnen
 
Q

Qui Si Parla Ca

Guest
tedk-<< I am looking at getting a carbon fork for my aluminum road bike. What are the
advantages/disadvantages of a fork with straight blades over one with a conventional raked design?

If the rake is the same-none other than looks. Stright is cheaper to make, BTW-

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"
 
J

Joshua Putnam

Guest
[email protected] (TedK618265) wrote in message
news:<[email protected]>...
> I am looking at getting a carbon fork for my aluminum road bike. What are the
> advantages/disadvantages of a fork with straight blades over one with a conventional raked design?

It's really an aesthetic difference more than anything.

Straight blades are a retro fashion statement, a look back to the days of high-wheeled Ordinaries.
Like those bikes of yore, a straight-bladed fork gets its offset in various ways other than curving
the blades, e.g. angling the blades where they leave the crown ("raking" the blades, as it was
called back in the 19th Century), offsetting the blades forward from the steerer at the crown, or
offsetting the axle ahead of the blades at the dropouts.

Straight blades have enjoyed quite a revival in recent years, perhaps because of the mountain bike
influence on cycling -- ever since the original RockShox, mountain bikes have mostly come with
straight-bladed forks, simply because that's the easiest way to make suspension forks, with
straight tubes.

If you're manufacturing lots of forks with identical geometry, it's also a bit less expensive to
do straight blades, at least in brazed steel, since you no longer need to bend the curve into
the blades.

--
[email protected] is Joshua Putnam <http://www.phred.org/~josh/> Braze your own bicycle frames. See
<http://www.phred.org/~josh/build/build.html
 
A

A Muzi

Guest
"TedK618265" <[email protected]> wrote in message
news:[email protected]...
> I am looking at getting a carbon fork for my aluminum road bike. What are
the
> advantages/disadvantages of a fork with straight blades over one with a conventional raked design?

Fashion. The effective rake can be achieved with a curved or an angled straight blade equally.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
 
Z

Zaf

Guest
Dave Lehnen <[email protected]> wrote in message news:<[email protected]>...
> TedK618265 wrote:
> > I am looking at getting a carbon fork for my aluminum road bike. What are the
> > advantages/disadvantages of a fork with straight blades over one with a conventional raked
> > design?
>
> Not much either way. The bending and torsional (twisting) stiffness will be nearly identical, for
> forks of similar construction. For loads directly up the fork, the straight-bladed fork will be
> stiffer, since it is then loaded in pure compression, while the curved fork has bending loads
> applied to it.

Hmmm, I had always assumed there would be SOME softening of the road if I switched my straight Al
fork with a curved (carbon or steel) one. As the force vector from the weight of your hand must
be in a straight line with the fork, I would expect this is the direction you feel most of the
road bumps from. The curving of carbon or steel will permit deflection in this direction as you
pointed out.

It is also intertesting to hear daves j's comment that all the deflection is in the crown. If this
is true (and he has not convinced me of that yet!), that means there is no damping at all of
compressive bumps up the fork blades.

I have never seen an curved aluminum fork, if there ever was such an animal this would lend
support to the theory that there is no deflection of the fork blades, deflection of aluminum would
be a bad thing.

More
> importantly, all straight-bladed forks are ugly, while most curved forks look good.<g>
>
> Dave Lehnen

Yah, the only toys I bought for my steed last year was a chain and a set of tires, I might buy that
carbon fork for just for vanity before these ben franklins burn a hold in my pocket!
 
M

Mark Hickey

Guest
[email protected] (Zaf) wrote:

>Dave Lehnen <[email protected]> wrote in message news:<[email protected]>...

>> Not much either way. The bending and torsional (twisting) stiffness will be nearly identical, for
>> forks of similar construction. For loads directly up the fork, the straight-bladed fork will be
>> stiffer, since it is then loaded in pure compression, while the curved fork has bending loads
>> applied to it.
>
>Hmmm, I had always assumed there would be SOME softening of the road if I switched my straight Al
>fork with a curved (carbon or steel) one. As the force vector from the weight of your hand must
>be in a straight line with the fork, I would expect this is the direction you feel most of the
>road bumps from. The curving of carbon or steel will permit deflection in this direction as you
>pointed out.
>
>It is also intertesting to hear daves j's comment that all the deflection is in the crown. If this
>is true (and he has not convinced me of that yet!), that means there is no damping at all of
>compressive bumps up the fork blades.

Hey, you can test your theory that you can compress those curved fork blades easily. Just tape a
piece of dental floss or other non-stretchy string tightly from the dropout to the crown and
push down for all you're worth. If you're compressing the fork the string will go slack. It
won't, though... the compressive force you'd need to get just a couple mm of bend would be
measured in tons.

>I have never seen an curved aluminum fork, if there ever was such an animal this would lend
>support to the theory that there is no deflection of the fork blades, deflection of aluminum would
>be a bad thing.

I'll remember that when I'm riding my fixie today with its Kinesis aluminum (curved) fork.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
M

Mike S.

Guest
"Mark Hickey" <[email protected]> wrote in message
news:[email protected]...
> [email protected] (Zaf) wrote:
>
> >Dave Lehnen <[email protected]> wrote in message
news:<[email protected]>...
>
> >> Not much either way. The bending and torsional (twisting) stiffness will be nearly identical,
> >> for forks of similar construction. For loads directly up the fork, the straight-bladed fork
> >> will be stiffer, since it is then loaded in pure compression, while the curved fork has bending
> >> loads applied to it.
> >
> >Hmmm, I had always assumed there would be SOME softening of the road if I switched my straight Al
> >fork with a curved (carbon or steel) one. As the force vector from the weight of your hand must
> >be in a straight line with the fork, I would expect this is the direction you feel most of the
> >road bumps from. The curving of carbon or steel will permit deflection in this direction as you
> >pointed out.
> >
> >It is also intertesting to hear daves j's comment that all the deflection is in the crown. If
> >this is true (and he has not convinced me of that yet!), that means there is no damping at all of
> >compressive bumps up the fork blades.
>
> Hey, you can test your theory that you can compress those curved fork blades easily. Just tape a
> piece of dental floss or other non-stretchy string tightly from the dropout to the crown and
> push down for all you're worth. If you're compressing the fork the string will go slack. It
> won't, though... the compressive force you'd need to get just a couple mm of bend would be
> measured in tons.
>
> >I have never seen an curved aluminum fork, if there ever was such an animal this would lend
> >support to the theory that there is no deflection of the fork blades, deflection of aluminum
> >would be a bad thing.
>
> I'll remember that when I'm riding my fixie today with its Kinesis aluminum (curved) fork.
>
My first M2 Road Pro came with one of those Kinesis forks. I still see a few of them around San
Diego... I actually just sold a carbon version of that fork. Same looks, different leg material.

Mike

> Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
A

A Muzi

Guest
> > TedK618265 wrote:
> > > I am looking at getting a carbon fork for my aluminum road bike. What
are the
> > > advantages/disadvantages of a fork with straight blades over one with
a
> > > conventional raked design?

> Dave Lehnen <[email protected]> wrote in message
news:<[email protected]>...
> > Not much either way. The bending and torsional (twisting) stiffness will be nearly identical,
> > for forks of similar construction. For loads directly up the fork, the straight-bladed fork will
> > be stiffer, since it is then loaded in pure compression, while the curved fork has bending loads
> > applied to it.

"Zaf" <[email protected]> wrote in message news:[email protected]...
> Hmmm, I had always assumed there would be SOME softening of the road if I switched my straight Al
> fork with a curved (carbon or steel) one. As the force vector from the weight of your hand must
> be in a straight line with the fork, I would expect this is the direction you feel most of the
> road bumps from. The curving of carbon or steel will permit deflection in this direction as you
> pointed out.
>
> It is also intertesting to hear daves j's comment that all the deflection is in the crown. If this
> is true (and he has not convinced me of that yet!), that means there is no damping at all of
> compressive bumps up the fork blades.
>
> I have never seen an curved aluminum fork, if there ever was such an animal this would lend
> support to the theory that there is no deflection of the fork blades, deflection of aluminum would
> be a bad thing.

"Dave"> More
> > importantly, all straight-bladed forks are ugly, while most curved forks look good.<g>

There are plenty of curved aluminum forks from Alan through Vitus to the SR-FX-Prizm (which was
quite popular only a few years ago). Yes a curved fork _might_ deflect an imperceptably small amount
more than a straight one ( depends on the material and gauges involved) but the range of motion
involved is miniscule either way compared to movement at the crown.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
 
J

Jobst Brandt

Guest
Fork rake, trail and offset, are uniquely different in bicycling than any other vehicle, the jargon
being confused by people unclear on the subject.

Check the 3rd listing for the word "rake" at:

http://www.m-w.com/

Rake in the normal vehicle world is the angle at which the steering axis is inclined as in cars,
motorcycles, and scooters... but not in bicycles where people thought that the curl (offset) at the
bottom looked like a garden rake and assumed that's to what the term meant. Rake is designed to
prevent fork failure from bending, although that is the mode in which forks normally fail anyway.
The angle is intended to take the statistically greatest road shocks in compression, making them act
axially on the fork blade.

With the common 700c wheel the rock or bump in the road of about 15-20mm height puts an axial
compression in the fork. Smaller bumps are less significant and larger ones rarer. Bicycles before
the day of paved roads had a lower rake for the rougher roads. Track bicycles generally have steeper
rake and could probably be even steeper, as we see in special bicycles for motor pacing and TTT.

Steering is mainly affected by trail (also known as caster) that should not be so great that is
steers the bicycle laterally when pedaling standing, where slide loads from leaning the bicycle act
laterally on trail. For this reason, fork offset is used to adjust trail, for any given rake, to a
stable straight ahead ride while reducing lean-steer.

Putting curl in the fork is a simple cold forming operation that is done on a shaped fixture by
hooking the dropout under a bolt and bending the blade manually. It is a trivial operation that
requires little time or skill. As has been mentioned, this does not make the fork springy and that
is why straight forks, angled at the fork crown for offset, perform identically to curled forks.

Maybe with the advent of suspension and straight blade forks, rake will return to an angle instead
of a garden rake.

Watch out for those rakish angles.

http://www.m-w.com/

See 2nd listing.

Jobst Brandt [email protected] Palo Alto CA
 
Z

Zaf

Guest
Mark Hickey <[email protected]> wrote in message
news:<[email protected]>...
> [email protected] (Zaf) wrote:
>
> >Dave Lehnen <[email protected]> wrote in message
> >news:<[email protected]>... It is also intertesting to hear daves j's comment that
> >all the deflection is in the crown. If this is true (and he has not convinced me of that yet!),
> >that means there is no damping at all of compressive bumps up the fork blades.
>
> Hey, you can test your theory that you can compress those curved fork blades easily. Just tape a
> piece of dental floss or other non-stretchy string tightly from the dropout to the crown and
> push down for all you're worth. If you're compressing the fork the string will go slack. It
> won't, though... the compressive force you'd need to get just a couple mm of bend would be
> measured in tons.
>
I take it you have done this? If so I am surprised the spring constant (that is a spring constant
is'nt it?) is this high.

> >I have never seen an curved aluminum fork, if there ever was such an animal this would lend
> >support to the theory that there is no deflection of the fork blades, deflection of aluminum
> >would be a bad thing.
>
> I'll remember that when I'm riding my fixie today with its Kinesis aluminum (curved) fork.

OK, so there are curved Al forks then pls help straighten out my misconceptions of materials. At
this point you have forced me to pull my yellow paged mtl sci book from the shelf. Ah, yes there it
is fatigue (at this point we're OT and back onto frame mtls methinks). I guess I had always assumed
that forks would deflect more then frames and Al frame loading was within the endurance limit of Al
whereas forks could not be. So what is a typical net deflection of a AL frame or fork?
 
M

Mark Hickey

Guest
[email protected] (Zaf) wrote:

>Mark Hickey <[email protected]> wrote in message
>news:<[email protected]>...

>> Hey, you can test your theory that you can compress those curved fork blades easily. Just tape a
>> piece of dental floss or other non-stretchy string tightly from the dropout to the crown and
>> push down for all you're worth. If you're compressing the fork the string will go slack. It
>> won't, though... the compressive force you'd need to get just a couple mm of bend would be
>> measured in tons.
>>
>I take it you have done this? If so I am surprised the spring constant (that is a spring constant
>is'nt it?) is this high.

I don't have to do it, I know how the test will come out. The curve isn't there as a "spring" but as
a way to provide proper trail while using a crown that's "square".

>> >I have never seen an curved aluminum fork, if there ever was such an animal this would lend
>> >support to the theory that there is no deflection of the fork blades, deflection of aluminum
>> >would be a bad thing.
>>
>> I'll remember that when I'm riding my fixie today with its Kinesis aluminum (curved) fork.
>
>OK, so there are curved Al forks then pls help straighten out my misconceptions of materials. At
>this point you have forced me to pull my yellow paged mtl sci book from the shelf. Ah, yes there it
>is fatigue (at this point we're OT and back onto frame mtls methinks). I guess I had always assumed
>that forks would deflect more then frames and Al frame loading was within the endurance limit of Al
>whereas forks could not be. So what is a typical net deflection of a AL frame or fork?

I don't know how to define "typical", but would say that an aluminum fork is much more
overengineered than the typical aluminum frame. The impromptu experiment I did shows that
deflections of plus/minus 10mm are certainly possible - though infrequent (I doubt anyone would ride
with constant brake shudder of that magnitude). The greatest flex in a bike frame occurs in the BB
area, where you can get enough deflection between the BB shell and front derailleur cage to cause
contact with the chain (yes, the BB spindle also plays a part, but much less than the frame in most
cases where there's a problem).

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
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