# Straight vs Curved Fork



## MerlinJude (Sep 7, 2009)

What are the pros and cons?
Thanks


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## Dave Hickey (Jan 27, 2002)

Looks....very little difference otherwise


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## CleavesF (Dec 31, 2007)

I've always had a "theory"... they are the same handling wise... but shouldn't straight forks be a bit lighter than their curved brethren?


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## freethelemmings (Jul 11, 2009)

This is simply my guess...my theory. It is based on nothing other than observation and reasoning:

A curved fork ought to be reliant on the frame. That is, if the geometry of the frame is more upright, or in other words, more tightly 'held together (if any of this makes sense, I'll be happy),' then there will be less clearance between the front of your toes and the tire. Thus, by 'bending' the fork, it puts the wheel further forward allowing for more clearance. 

W/r/t weight, I think it's a non-factor. I feel that if you bend the fork, you will need to supplement with a stronger material. Whether it's a higher quality steel, or tougher carbon, you have to make up for the loss of structure somewhere.

Now just don't ask me the reason for a frame that is built more upright. I'm still forming my opinion on geometries.


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## Voodoochile (Apr 10, 2009)

I always wondered if a bent fork would be more supple compared to a straight bladed fork. It would seem to me that the bend would work just as you see the curved seat stays being designed these days. Instead of transferring road buzz straight up through blade it would be more shock absorbing.
This is only my opinion being in the tool and die design trade. I have not scientifically tested this theory though.


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## george kraushaar (Jan 15, 2007)

I replaced a curved carbon fork on a Bianchi Voloce with a straight carbon fok and did notice some difference in suppleness. Then again, the blades on the curved fork were more tapered than the straight bladed fork as well.


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## twinkles (Apr 23, 2007)

Easton says there is no difference in the ride.


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## sometimerider (Sep 21, 2007)

freethelemmings said:


> then there will be less clearance between the front of your toes and the tire. Thus, by 'bending' the fork, it puts the wheel further forward allowing for more clearance.


I don't think so. Straight forks, at least all those I've seen on road bikes, aren't really straight. They have a bend right below the head tube:

View attachment 179608


Thus they can have exactly the same trail as a curved fork. See this for a description of fork trail.

IMO, a curved fork, given otherwise similar geometry and materials, is less likely to break (the bend point of a straight fork is a high stress point) and provides better suspension.

Other things being equal, a curved fork is better.


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## freethelemmings (Jul 11, 2009)

sometimerider said:


> I don't think so. Straight forks, at least all those I've seen on road bikes, aren't really straight. They have a bend right below the head tube:
> 
> 
> Thus they can have exactly the same trail as a curved fork. See this for a description of fork trail.
> ...


I see. That would seem to make sense- in other words, a curved fork provides tighter handling because you are essentially steering directly under the wheel vs. out in front of your wheel, yes?

Good stuff.


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## sometimerider (Sep 21, 2007)

freethelemmings said:


> I see. That would seem to make sense- in other words, a curved fork provides tighter handling because you are essentially steering directly under the wheel vs. out in front of your wheel, yes?


The quickness of the handling is largely determined by the head tube angle and the amount of trail (less trail implies quicker steering). Since straight and curved forks can be identical in those measures, they could be exactly the same with respect to quickness.

(Of course, quicker steering implies twitchier handling - so it's a trade-off.)


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## JimP (Dec 18, 2001)

I think it may depend on the actual forks as to which absorbs more vibration. I had an Aegis Aro Svelte with a curved fork that you could see bend when I put a lot of weight on the front. That fork really did absorb a lot of vibration compared with the Straight Oval Concepts A900 Jetstream TT fork on my Zaero. The straight Felt fork on my F5 is more compliant than the OC but not as much as the Aro.


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## bane (Aug 30, 2006)

There's a blog entry from Moulton talking about this. He favors curved fork blades. 

In reality I don't think it makes much difference other than style.


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## Peter P. (Dec 30, 2006)

There are too many variables to make a sound conclusion about the differences between a curved and straight bladed fork. You'd have to make two identical forks, less the straight vs. curved blades, to measure any real differences and in the real world you're likely comparing two forks with many differences among them.

Any two forks, straight and curved, can place the front wheel at the same spot on the road so their handling characteristics should be the same. The fork's reaction to bumps is more a function of blade diameter, profile, taper, wall thickness, and material. True, a curved blade is likely heavier than a straight blade but the weight difference is hardly worth debating. This holds true for carbon as well as steel and even aluminum forks.

One framebuilder I spoke with said he noticed that once he began to bend a fork blade to impart a curve into it, it would bend easier. He thought the end result would be a softer riding fork than a straight blade, but even he wasn't totally convinced.

You really have to rely more on reviews and test rides to find which fork appeals to you.


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## buck-50 (Sep 20, 2005)

Depends on the material, too.

2 steel forks with the same bend might ride differently depending on whether the builder cut the excess material from the fat end or the thin end of the fork tubes...

Carbon can probably be formed into about any shape and give you a certain set of ride characteristics. Though it explodes when exposed to sunlight.

And Aluminum forks tend to be harsh no matter how you build them, except for the ones that aren't harsh at all.


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## Mel Erickson (Feb 3, 2004)

Dave wins. The furst answer is the bestest answer and the writest answer.

It's akin to which bike frame material rides the softest/stiffest. There is no right or wrong answer as they can both be designed to perform however the designer wants them to perform.


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## Kerry Irons (Feb 25, 2002)

*No*



freethelemmings said:


> I see. That would seem to make sense- in other words, a curved fork provides tighter handling because you are essentially steering directly under the wheel vs. out in front of your wheel, yes?


Completely wrong. As others have noted repeatedly, but you apparently are not grasping, whether a fork is straight or curved, the wheel is in the same place if the offset (sometimes incorrectly called rake) of the fork is the same.


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## twinkles (Apr 23, 2007)

JimP said:


> I think it may depend on the actual forks as to which absorbs more vibration. I had an Aegis Aro Svelte with a curved fork that you could see bend when I put a lot of weight on the front. That fork really did absorb a lot of vibration compared with the Straight Oval Concepts A900 Jetstream TT fork on my Zaero. The straight Felt fork on my F5 is more compliant than the OC but not as much as the Aro.


I should have mantioned that Easton makes the ec90 sl in straight and curved. Given everything else being the same, Easton says their straight and curved forks ride the same. So I think that you are right saying it depends on the actual forks.


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## freethelemmings (Jul 11, 2009)

Kerry Irons said:


> Completely wrong. As others have noted repeatedly, but you apparently are not grasping, whether a fork is straight or curved, the wheel is in the same place if the offset (sometimes incorrectly called rake) of the fork is the same.


Wow Kerry. Thanks for the flame. I guess sometimerider's answer wasn't sufficient for you:



sometimerider said:


> The quickness of the handling is largely determined by the head tube angle and the amount of trail (less trail implies quicker steering). Since straight and curved forks can be identical in those measures, they could be exactly the same with respect to quickness.
> 
> (Of course, quicker steering implies twitchier handling - so it's a trade-off.).


May the Bike Gods take pity on my ignorance. I only hope that it's not too late for future generations.:frown2:


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## laffeaux (Dec 12, 2001)

They ride the same, however a straight fork looks better.  Unless it's a mid-80s or earlier bike and then curved looks much better.


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## BentChainring (Jun 23, 2005)

Two forks on an identical frame/rider/etc.

Fork one - "straight" (ie, with no "rake)
Fork two - some amount of rake (forward offset)

The bike with Fork one will have poorer handling at lower speeds, and may 'feel' a big sluggish at higher speeds... in other words, you will feel like you need to drag the bike into a lean to get it to corner..

The bike with Fork two will have better handling at lower speeds, and should 'feel' more responsive at higher speeds...in other words, you will be able to get the bike to corner with less lean... this is only true up to some point when the bike tends to be overly 'twitchy'..

This qualitative analysis comes from a book called "Lords of the Chainring" by B. Patterson... it isnt in print, but copies can be had. It is, quite honestly, the only book written on bicycle stability and design that has been proven over and over to be fairly accurate. The formula's contained within his book work for both upright and recumbents, and is part of a class taught at Cal Poly SLO...


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## BentChainring (Jun 23, 2005)

I should add to my above post that it does not take into account the compliance of the fork, or the structure of its attachment to the frame... this can make a big difference, but for the purposes of this description, I spoke from a purely geometric dynamic point of view.


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## BentChainring (Jun 23, 2005)

sometimerider said:


> IMO, a curved fork, given otherwise similar geometry and materials, is less likely to break (the bend point of a straight fork is a high stress point) and provides better suspension.
> 
> Other things being equal, a curved fork is better.


This is a case of "it depends"

Lets start by just looking at the crown. Regardless of fork curvature, for a given offset fork, the crown will see the same stress. In other words the crown does not know if the fork is straight or curved, it just knows that there is X amount of offset, and therefore a moment of Y (Force x Lever arm length). Now, if we look at geometry of the crown and steerer, the *highest stress is going to be located at the interface of the steerer and the crown*. This is true for ANY fork... straight, curved, etc...

Now...again, assuming the same fork offset... if we look at how you transmit the load from the axle centerline to the crown you can either have a straight beam in bending (straight fork) or a curved beam in bending (curved fork). Simple. Now... I had to consult my machinery design textbook for this... but the stress distribution for a curved beam, bent in the plane of bending (ie... how a bike fork is loaded in normal operation) is hyperbolic with the highest stress at the smaller radius (that is, at the front of the fork). Luckily, this point of highest stress is in compression, and will not cause metal fatigue.

ANother thing to consider, is that when a metallic fork blade is formed, it is bent cold. This means there are residual compressive stresses at the back of the fork, and residual tensile stresses in the front. Therefore, when loaded in normal operation, you are trying to relieve the residual stresses that were left in the fork during forming (assuming they persist through brazing). This *greatly* increases fatigue life of metallic components.

Carbon is another thing. It will simply explode if you don't set your tire pressure to exactly 7.2bar, and have your bike computer set to Kph

:thumbsup:


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## laffeaux (Dec 12, 2001)

BentChainring said:


> Two forks on an identical frame/rider/etc.
> 
> Fork one - "straight" (ie, with no "rake)
> Fork two - some amount of rake (forward offset)


Fork two does not exist on a real bike in reality. Straight forks (that are actually for sale and used on bikes) are available with identical offsets to curved-blade forks. "Straight" forks most often achieve their offset by having the fork angle differ from the steerer tube angle (on some mountain bike forks, the angle is achieved by offsetting the dropout form the fork).

Identical "trail" numbers can be achieved with either type of fork.


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## BentChainring (Jun 23, 2005)

laffeaux said:


> Fork two does not exist on a real bike in reality. Straight forks (that are actually for sale and used on bikes) are available with identical offsets to curved-blade forks. "Straight" forks most often achieve their offset by having the fork angle differ from the steerer tube angle (on some mountain bike forks, the angle is achieved by offsetting the dropout form the fork).
> 
> Identical "trail" numbers can be achieved with either type of fork.


I think your referring Fork one... the straight -zero offset fork.

They may not exist in production ( I am not aware either way ), but they CAN be produced... and by changing the head tube angle you can produce a bike with almost identical handling.

Trail is the important number, not head tube angle or offset on its own. Many recumbents that I have worked with (high speed fully faired recumbents) typically have negative fork rake. This functions to increase trail MUCH more than would be necessary on an upright bicycle to give the bike more yaw authority.


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## sometimerider (Sep 21, 2007)

BentChainring said:


> This is a case of "it depends".


Doesn't it always.

I think what you're saying matches (and in a few spots, exceeds) my understanding of the issues at play (hey, I've had some physics and engineering classes).

With a curved fork, the stresses endured when an impulse tries to compress the fork are distributed over the curved portion. In a straight fork, they are concentrated right at the bend below the head tube. I think the latter is harder to deal with and less likely to be both strong enough and able to behave elastically. 

Thanks, Bent.


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## BentChainring (Jun 23, 2005)

sometimerider said:


> Doesn't it always.
> 
> I think what you're saying matches (and in a few spots, exceeds) my understanding of the issues at play (hey, I've had some physics and engineering classes).
> 
> ...


Yep... but with a curved fork, you get the same stress at the bottom of the head tube. The shape of the fork doesn't matter to the crown. All it knows is someone is bending the crap out of it, and if the rake is the same, the moment is the same.

phew... I should go build a bike or something, eh?


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## sometimerider (Sep 21, 2007)

BentChainring said:


> Yep... but with a curved fork, you get the same stress at the bottom of the head tube. The shape of the fork doesn't matter to the crown. All it knows is someone is bending the crap out of it, and if the rake is the same, the moment is the same.


I'm not sure that's true if one fork can better act as a spring than another. And I think a curved fork does. If the fork's design can absorb impulses, the crown will see less stress.

A straight (but angled) fork can also act as a spring, but most of the bending stresses are concentrated at one point.


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## BentChainring (Jun 23, 2005)

sometimerider said:


> I'm not sure that's true if one fork can better act as a spring than another. And I think a curved fork does. If the fork's design can absorb impulses, the crown will see less stress.
> 
> A straight (but angled) fork can also act as a spring, but most of the bending stresses are concentrated at one point.


The 'springy-ness' of the fork doesnt matter since something has to react to the loads of the spring (the crown).

Maybe we are thinking of different affects... I am merely talking about the load from my fat arse sitting on the bike. I think you may be considering hitting something from the front. In that case, you may get higher loads in the straight fork... Ill have to think about that one...


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## sometimerider (Sep 21, 2007)

BentChainring said:


> Maybe we are thinking of different affects... I am merely talking about the load from my fat arse sitting on the bike. I think you may be considering hitting something from the front. In that case, you may get higher loads in the straight fork... Ill have to think about that one...


You're right, I haven't been talking about static loads. That shouldn't be a significant design issue. It's the dynamic loads, such as when you hit a pothole, that can break a fork. And how the fork responds to them contributes to ride comfort (a very important issue to me and my arthritic wrists).


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## HMBAtrail (Jan 8, 2008)

BentChainring said:


> Two forks on an identical frame/rider/etc.
> 
> Fork one - "straight" (ie, with no "rake)
> Fork two - some amount of rake (forward offset)
> ...


Not entirely sure what you are going for on the above statement. Straight blade doesn't mean "zero offset". A straight bladed fork can, and often does, have the same rake as a curved blade. A zero offset fork I am sure has application (the acrobatic bikes come to mind) but for practical road or mountain bike purposes they don't exist. In order to get a trail measurement of 60mm with a zero-offset fork you would need an ~80 degree head angle. See what I'm saying? 

On lugged forks, for example, a straight bladed fork has the crown offset by 6 or 7 degrees, thus providing the rake of the fork. For curved blades, there is no offset in the crown and the rake is determined by how much curve you put in the blade. Take a curved blade fork and a straight bladed fork with identical axle to crown measurements and the same offset (rake) and there would be nary a whit of difference between how the bike rides.

Technically speaking, you could have a curved blade with zero offset if you did two bends on it. One rearward and the other forward. Or, I suppose you could have a curved blade with negative rake if you simply installed it backward.

What I am getting at is two forks with the same rake will have the same handling characteristics. There is no "sluggish" feeling simply because a straight blade is used. The characteristics you are describing are a result of trail. 

As has been said several times already, the difference is largely aesthetics.


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## Voodoochile (Apr 10, 2009)

Okay so why were most of the older bikes built with a curved fork? I honestly don't know if straight bladed forks have been around all along but I always remember seeing curved forks. It seems like it would be easier to make a straight fork (maybe I'm wrong). Why would the builders go to the trouble of bending the blades?


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## Voodoochile (Apr 10, 2009)

Does this answer my question? Hmmm
http://en.wikipedia.org/wiki/Bicycle_fork


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## HMBAtrail (Jan 8, 2008)

Voodoochile said:


> Okay so why were most of the older bikes built with a curved fork? I honestly don't know if straight bladed forks have been around all along but I always remember seeing curved forks. It seems like it would be easier to make a straight fork (maybe I'm wrong). Why would the builders go to the trouble of bending the blades?


Variety is the spice of life. Some like it one way while others like at another. Ain't life grand?

But, yes it is easier to build a straight bladed fork simply because you don't have to go through the process of bending the blades. But, the additional work is minor.


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## Voodoochile (Apr 10, 2009)

HMBAtrail said:


> Variety is the spice of life. Some like it one way while others like at another. Ain't life grand?
> 
> But, yes it is easier to build a straight bladed fork simply because you don't have to go through the process of bending the blades. But, the additional work is minor.


So why on earth would you bend it? Looks? Shock absorbsion? I would only guess the later would be a reasonable explanation for the curve. Maybe it's just a learning curve.


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## HMBAtrail (Jan 8, 2008)

Voodoochile said:


> So why on earth would you bend it? Looks? Shock absorbsion? I would only guess the later would be a reasonable explanation for the curve. Maybe it's just a learning curve.


The best guess would be tradition. Lugged fork crowns that require bending the blades have been around for years and years. Those that have the rake built into the crown are more recent. (Disclaimer: I am certain there are examples of straight bladed forks going back 100 years but humor me). Hell, try finding a track crown for straight blades. You'll be looking for quite a while. 

Did fork crowns with the offset built in come into vogue because people demanded it? Was it coincidental with the advent of investment cast crowns versus pressed steel? Was it to speed the build process by eliminating a step? 

I'm not sure on any of these nor do I think it is overly important in the world we live. I think it is great that there are options.


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## Voodoochile (Apr 10, 2009)

Maybe the early builders found it was easier to achieve the offset by bending the blades and attaching the steer tube and crown straight.
I'm a tool and die maker and work with steel all day every day for over 20 years. I've also designed many dies and machines for production and personally the only time I would bend something is for ease of application, unless there was a very good outcome for the reason of the bend. Everything we do is built from an idea. Bending is not easy for me unless I have a machine to make the bend consistently and accurately.
I’m not looking to get flamed. LOL


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## Voodoochile (Apr 10, 2009)

Just thinking realy quick. If I were going to build a fork which I have no experience at all. We build dies mainly to stamp out parts with many forms and bends like a bottle opener for example. If I were to build many I may fasten the steer tube and crown straight to save time cutting and welding angles. I may then build a machine to bend the blades to achieve the offset. How do the builders bend the fork blades on a steel frame? They don't do it by hand do they? Or does the tubing co. do that for them when they mfg. the tubes. This of course leaves out CF and Al.
I know I'm pushing it guys but I'm interested.


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## Dave Hickey (Jan 27, 2002)

Voodoochile said:


> Just thinking realy quick. If I were going to build a fork which I have no experience at all. We build dies mainly to stamp out parts with many forms and bends like a bottle opener for example. If I were to build many I may fasten the steer tube and crown straight to save time cutting and welding angles. I may then build a machine to bend the blades to achieve the offset. How do the builders bend the fork blades on a steel frame? They don't do it by hand do they? Or does the tubing co. do that for them when they mfg. the tubes. This of course leaves out CF and Al.
> I know I'm pushing it guys but I'm interested.



Most(all?) tubesets come pre-bent...I have a Reynolds 531 tubeset in my garage... It has the fork blades already bent...


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## HMBAtrail (Jan 8, 2008)

Dave Hickey said:


> Most(all?) tubesets come pre-bent...I have a Reynolds 531 tubeset in my garage... It has the fork blades already bent...


I have never bought or used a pre-bent fork blade. This is how I do fork blades and seat stays. I have a different bender for top tubes.


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## Dave Hickey (Jan 27, 2002)

HMBAtrail said:


> I have never bought or used a pre-bent fork blade. This is how I do fork blades and seat stays. I have a different bender for top tubes.


Cool...I didn't know that..good to know that some builders still bend their forks


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## paredown (Oct 18, 2006)

Couple of points--it seems that if Ernesto is telling the story at all accurately, he came up with the design for the Precisa straight bladed fork because he was challenged by the Ferrari materials guys who asked point blank, "Why do you bend the forks?" E answers "for handling/damping." "Let's test" said the Ferrari guys.

And they found no significant improvement with traditional curved forks vs a straight fork bent at the crown and the latter had advantages (stronger because of no residual stress from cold bending). And the Precisa was the result.

But I think for a lot of years, conventional wisdom was that you had to curve the fork blades for ride comfort.

Second point is where the stress is--wasn't it Ritchey who first made a headset with a larger bottom frame cup precisely because it carried more stress?


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## DY123 (Oct 5, 2006)

I think that with current modern racing frames and forks there is very little difference, feel wise (if any at all).

Old frames with high rake forks with very thin tips may behave differently. I can see that as a reason they bent blades 100 years ago (a sort of spring suspension). I've never ridden one so it is just a guess.

Dave, I've never used a pre-raked blade. Everyone I know bends their own. It is a way to further customize the look. I have a special bending mandrel that gives my forks, "my bend". I like very gradual curves. I also like straight blades.

Also when talking about the bending and residual stresses, compression, tension.....you have to consider the heat of brass brazing the tips in. What does that do to the stress? As well, some builders anneal the blades at the curve. There are so many variables.


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## Mel Erickson (Feb 3, 2004)

That red fork on the wall in the background has some MAJOR offset and funky looking thingies at the bend.


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## Voodoochile (Apr 10, 2009)

That's some of the info I was after from you guys that build your own forks. Thanks for posting that stuff. Do you guys also build straight forks? I would imagine you do. If you were to suggest a fork it kind of seems like it all boils down to style then. I was guessing that fork bending by hand would involve heat but I guess bending them cold does the trick just with a special tubing bender. I'm glad I asked all my pushy questions. Thanks for not flaming me. LOL


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## Voodoochile (Apr 10, 2009)

paredown said:


> Couple of points--it seems that if Ernesto is telling the story at all accurately, he came up with the design for the Precisa straight bladed fork because he was challenged by the Ferrari materials guys who asked point blank, "Why do you bend the forks?" E answers "for handling/damping." "Let's test" said the Ferrari guys.
> 
> And they found no significant improvement with traditional curved forks vs a straight fork bent at the crown and the latter had advantages (stronger because of no residual stress from cold bending). And the Precisa was the result.
> 
> ...


Where did you find that story about Colnago? I'd like to read that.


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## Voodoochile (Apr 10, 2009)

On a straight blade fork... I'm guessing the steer tube is welded to the crown on an angle then to achieve the offset. Is that right?


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## BentChainring (Jun 23, 2005)

Voodoochile said:


> On a straight blade fork... I'm guessing the steer tube is welded to the crown on an angle then to achieve the offset. Is that right?


If it has offset, then yes.

There is no reason you are required to have fork offset.


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## BentChainring (Jun 23, 2005)

DY123 said:


> Also when talking about the bending and residual stresses, compression, tension.....you have to consider the heat of brass brazing the tips in. What does that do to the stress? As well, some builders anneal the blades at the curve. There are so many variables.


If you braze the tips in after bending the forks, you will probably relieve most of the residual stresses left in the fork. Assuming the material is something like 4130 steel, my reference book puts the annealing temperature at 1450-1550 ( Modern Steels - Bethlehem Steel). See the color reference below. I would imagine you would not get all the way to 1450, but close enough that some stress relief takes place. Time is also a factor here, so it depends how long you hold it at temp.

Personally... I would not anneal the bends. Why? Those are beneficial residual stresses. If you are loading a bent beam, in the same direction it was yielded plastically, you dramatically increase the stress life. If you want a better description of why this occurs please let me know.


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## Voodoochile (Apr 10, 2009)

BentChainring said:


> If it has offset, then yes.
> 
> There is no reason you are required to have fork offset.


Okay so let me ask you this...
I bought a Casati frame off eBay NOS and I don't like the fork. Money is tight but I was looking at this Soma fork with a 41mm offset ($130). I've read that most road racing bikes use between 43-45 offset. I've seen track forks with even less offset. I'm not sure of the HTA on the frame but it looks kind of steap. Would the fork with 41mm offset ride alot different from a 43mm.? How would it ride different? Why does Soma use this offset instead of the standard 43mm I've seen on other forks? I'm not sure how it would ride with that offset so I want to get some advice.








Soma Fork with 41mm offset...


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## BentChainring (Jun 23, 2005)

Voodoochile said:


> Okay so let me ask you this...
> I bought a Casati frame off eBay NOS and I don't like the fork. Money is tight but I was looking at this Soma fork with a 41mm offset ($130). I've read that most road racing bikes use between 43-45 offset. I've seen track forks with even less offset. I'm not sure of the HTA on the frame but it looks kind of steap. Would the fork with 41mm offset ride alot different from a 43mm.? How would it ride different? Why does Soma use this offset instead of the standard 43mm I've seen on other forks? I'm not sure how it would ride with that offset so I want to get some advice.


Have you ridden the bike with the 43mm offset?

By decreasing offset, you will be increasing the trail. Trail is the length difference between the projected head tube angle on the ground, and the tire contact point. In this case you would be gaining 2mm of trail. Adding trail increases the low speed stability of the bicycle. In other words, you can ride the bike at a lower speed and be able to correct for tipping over easier, since you have more yaw authority for a given roll.

That said. I would wager that the difference between 43, and 41mm is almost imperceptible unless you had raced the 43mm for years, and were now switching to a 41.

Offset is only one part of trail. The other part of trail is the head tube angle. Hang on... Let me draw a picture....


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## Voodoochile (Apr 10, 2009)

Honestly I don't know if the fork on the frame has a 43mm. I won't get it until tomorrow. I'm just guessing the fork that came with the frame is standard but I guess I can measure it when I get it. So with more trail does it steer slower or faster?


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## BentChainring (Jun 23, 2005)

Voodoochile said:


> Honestly I don't know if the fork on the frame has a 43mm. I won't get it until tomorrow. I'm just guessing the fork that came with the frame is standard but I guess I can measure it when I get it. So with less trail does it steer slower or faster?


Less trail = less yaw authority.

You can "steer" the same speed. However, a bicycle with less trail will require more roll to induce the same yaw... In other words, a bike with less trail will require more lean for the same cornering as a bike with more trail.


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## BentChainring (Jun 23, 2005)

Oh... and "why" do different manufacturers use different offsets?

I dont know... but you can build two identical handling bicycles, with different fork offsets, and head tube angles. But as long as the trail is the same, the bike will handle virtually the same.


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## Voodoochile (Apr 10, 2009)




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## Voodoochile (Apr 10, 2009)

Okay so if I get this right more trail would make the ride more twitchy? Harder to ride with no hands. My Colnago CT-1 was very hard to ride with no hands and twitchy and my Tommasini Tecno seems slow to turn like I need to lean alot more to get it to turn.


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## ultimobici (Jul 16, 2005)

Voodoochile said:


> Okay so let me ask you this...
> I bought a Casati frame off eBay NOS and I don't like the fork. Money is tight but I was looking at this Soma fork with a 41mm offset ($130). I've read that most road racing bikes use between 43-45 offset. I've seen track forks with even less offset. I'm not sure of the HTA on the frame but it looks kind of steap. Would the fork with 41mm offset ride alot different from a 43mm.? How would it ride different? Why does Soma use this offset instead of the standard 43mm I've seen on other forks? I'm not sure how it would ride with that offset so I want to get some advice.
> 
> 
> ...


Your Casati's fork is period right for an mid 90's Italian frame. The Soma is quite likely designed with their frame's geometry in mind hence the 41mm rake. Build the frame up with the intended fork and at least see how it rides as Casati intended. Then look at replacing the forks. By bolting a different fork into it you'll possibly kill the handling and ride characteristics. Casati have probably forgotten more about frame building than Soma know too!


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## BentChainring (Jun 23, 2005)

Voodoochile said:


> Okay so if I get this right more trail would make the ride more twitchy? Harder to ride with no hands. My Colnago CT-1 was very hard to ride with no hands and twitchy and my Tommasini Tecno seems slow to turn like I need to lean alot more to get it to turn.


Not necessarily.... bikes are an interesting thing... people can learn to ride almost anything.

Dont think about it too much. Put the wheels on the ground, and get rolling! :thumbsup:


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## saird (Aug 19, 2008)

The main one: straight looks miles better. :thumbsup:


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## Specialized6000 (Aug 22, 2009)

what about the wavy forks on Pinarello's? now thats a whole another debate


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## Len J (Jan 28, 2004)

Lots of crap info in this thread.......

First off, you can't look at the performance of a fork seperate from the bike when evaluating differences. Assuming the same rake, the only difference between 2 well designed forks, a straight one and a curved one is aestetics.....the straight one will be butt ugly. 

Any other difference is pure hoo haa.

Len


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## Voodoochile (Apr 10, 2009)

ultimobici said:


> Your Casati's fork is period right for an mid 90's Italian frame. The Soma is quite likely designed with their frame's geometry in mind hence the 41mm rake. Build the frame up with the intended fork and at least see how it rides as Casati intended. Then look at replacing the forks. By bolting a different fork into it you'll possibly kill the handling and ride characteristics. Casati have probably forgotten more about frame building than Soma know too!


Yes I agree. I think I'll leave the intended fork. You're right.


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## Frith (Oct 3, 2002)

To the guy that bends his own forks....

Bet ya can't wait for the future.


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## HMBAtrail (Jan 8, 2008)

BentChainring said:


> If it has offset, then yes.
> 
> There is no reason you are required to have fork offset.


Actually, no, you don't. You do not weld the steer tube at an angle to the fork crown to achieve rake. I have never seen or heard of such a proposition.

Again, if the fork crown is for straight fork blades then the rake is in THE FORK CROWN. You do nothing different with the steer tube whether it is straight bladed or curved.

No, you aren't _required_ to have offset but if you want to ride a normal bike I might suggest a fork with rake. As I stated in an earlier post, a fork with zero rake requires a head tube angle of approximately 80 degrees to get 60mm of trail. If you have a frame with a 73 degree head angle you need about 43mm of rake to get your 60mm of trail. 

For the eleventeenth time, the difference is aesthetics. Go with the fork that speaks to you.

-EDIT- Now that I think more on it, I suppose in the case of a unicrown fork you would _technically_ weld the steer tube at an angle because the fork doesn't really have a crown. But, it is an odd way of thinking it to assume you derive your rake from the steer tube.


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## HMBAtrail (Jan 8, 2008)

Len J said:


> Lots of crap info in this thread.......
> 
> First off, you can't look at the performance of a fork seperate from the bike when evaluating differences. Assuming the same rake, the only difference between 2 well designed forks, a straight one and a curved one is aestetics.....the straight one will be butt ugly.
> 
> ...


Agreed on all counts except for the straight blade looking ugly. On the right bike they look good. A lot of the cyclocross forks I have built are straight bladed.


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## HMBAtrail (Jan 8, 2008)

Voodoochile said:


> That's some of the info I was after from you guys that build your own forks. Thanks for posting that stuff. Do you guys also build straight forks?


Yup.


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## HMBAtrail (Jan 8, 2008)

Other times, curved bladed forks look better. Pictures are fun!



















This is another straight one:


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## Dave Hickey (Jan 27, 2002)

beautiful frames...

I went straight blade on my custom only because I liked the look


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## DY123 (Oct 5, 2006)

Bent Chainring.... When I said "What does that do to the stress?”, it was a rhetorical question. You were discussing the engineering of the fork…but missing one big component, the heat involved in the production cycle. I think it is important to look at the entire process when discussing the characteristics of the material.

I don’t anneal my forks, but I know some Masters that do. I don’t hear of their forks failing. They did it to change the characteristics of the blade.


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## Len J (Jan 28, 2004)

HMBAtrail said:


> Other times, curved bladed forks look better. Pictures are fun!
> 
> 
> 
> ...


When I think of ugly forks, I think of wound-up..........I wouldn't put one of those on my ex-wife's bike.  

Len


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## Voodoochile (Apr 10, 2009)

ultimobici said:


> Your Casati's fork is period right for an mid 90's Italian frame. The Soma is quite likely designed with their frame's geometry in mind hence the 41mm rake. Build the frame up with the intended fork and at least see how it rides as Casati intended. Then look at replacing the forks. By bolting a different fork into it you'll possibly kill the handling and ride characteristics. Casati have probably forgotten more about frame building than Soma know too!


After receiving the frame-set I would never break this up. I didn't think it was going to be this nice. I'm actually blown away because it looks ten times better in person. As good as any De Rosa or Cinelli I've seen and that's saying a bit. The paint and chrome looks better than my Tecno too. I really didn't think the paint and chrome looked as good as I expected on my Tecno though considering the price of that frame set. This thing was an absolute bargain at $550. The fork looks pretty good to me now. An engraved crown would be sweet but it is what it is and I'm more than satisfied. I can't wait to ride this thing. I checked the STA (73.5) and HTA (73) with one of my machinist protractors from work and it's exactly what I was looking for too. I looked for the angles everywhere on the web but only found some angles from other Casati frames and they weren’t exactly what I would have liked but this frame is more standard it seems which is good. Shame on me for wanting to put a Soma fork with this frame. Wow!


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## paredown (Oct 18, 2006)

Voodoochile said:


> Where did you find that story about Colnago? I'd like to read that.


I know I read a longer version somewhere, but if you have teh patience, he tells the story midpoint in this video interview:

Colnago Interview


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## nenad (May 5, 2004)

Dave Hickey said:


> beautiful frames...
> 
> I went straight blade on my custom only because I liked the look


Very interesting. I went with curved forks on both of my bikes because that's what they came with


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## BentChainring (Jun 23, 2005)

DY123 said:


> Bent Chainring.... When I said "What does that do to the stress?”, it was a rhetorical question. You were discussing the engineering of the fork…but missing one big component, the heat involved in the production cycle. I think it is important to look at the entire process when discussing the characteristics of the material.
> 
> I don’t anneal my forks, but I know some Masters that do. I don’t hear of their forks failing. They did it to change the characteristics of the blade.


Depends when/if you braze the dropouts in, and how long the fork is hot. I am not sure if the annealing kinetics in Chrome Moly steel are fast enough to allow full stress relief with the brazing times we are talking about. 

I never said the forks would fail. I simply said the stress state of an un-annealed fork is preferential to an annealed one. 

What characteristics are they changing?


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## DY123 (Oct 5, 2006)

It is hard to estimate.....but I'd say around 8 - 10 minutes at 1600F. (I've never timed it, so I could be off a bit). That brazing is done 4 or 5 inches from the bend. The entire blade gets hot.

They are trying to make it a smoother ride. Help "soften" the blade in certain areas.....AFAIK. I'm not sure how many builders still do it. I know of one though.


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