# The Thinking Behind Straight Forks



## RoadBoy1 (Oct 1, 2011)

I have a Specialized Allez Compact road bike and I have been trying to soften up the ride just a bit seeing as how I no longer race and am mostly interested in comfortable rides to maintain my fitness and get out side to enjoy myself. One thing I am noticing and it seems to be tied to the emergence of carbon fibre as a material to make bikes is that just about every fork I see on a carbon bike is a straight blade fork and I am curious about the justification for this.

Every bike I have owned and ridden I have compared to my very first pro level bike, a Raleigh Pro Mk 4 and obviously that bike had a steel curved fork. When I look at photos of the bike 90% of the rake was in the last 6" of the fork and that bike has a magic carpet ride and tracked straight as a laser.

My father was a structural engineer and from working with him on some of his projects I have a good understanding of engineering. I know from sailing high performance boats that design and lay-up of carbon fibre is ridiculously expensive (much more so that it really needs to be) so I can't help but wonder if the advent of carbon fibre forks with straight legs is a thinly veiled attempt by the bike makers to stick it to the consumers and keep their profits high at the same time. My first carbon fork was on my Colnago and it was a Kestrel EMS fork with curved legs and it had a nice ride for a racing fork. If a maker can save $25 per fork on design costs and $50 per fork on lay-up and mold costs by making a carbon fibre fork with straight legs as opposed to one with curved legs and not pass the cost savings along to the consumer the bike and fork makers have come up with a nice little payday. If you think about a $75 saving per fork and possibly 100,000 or more forks made somebody is making a killing while sticking the consumer with an inferior product that rides like you have a baseball bat up your rear.

That's my take on this and I would enjoy hearing from the members of this forum as to their thoughts and feelings. Thanks.


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## tdietz87 (Apr 19, 2011)

While I am not educated on the costs of developing carbon fiber molds, I do not think the costs of "wavy" or curved forks is nearly $75 a piece higher. Quite frankly I think thats probably a lot more than the entire fork costs.

I remember reading somewhere (don't recall where, probably the pinarello forum) that a Pinarello Dogma costs around $200. And their frames and forks are definitely far from straight.

This article claims avg cost to produce bike is $265 How soon does a bike pay back its initial carbon footprint?* - Slate Magazine

My father is also an engineer (tool and die) and has explained to me every extra bend, dent, hole, etc. costs more money, but I think its very far from $75 a piece. I ride a cervelo and would like to think that with all their R&D into aerodynamics, we would see the best they have to offer. Even their $10,000 handmade frame has straight forks. The new s5 and new p5 are the newest and "best" in aero but are fairly straight. Perhaps straight is fastest, but not the most comfortable. Not sure if I'd say inferior, rather comfort isn't the main goal.

Just my 2 cents.


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## 88 rex (Mar 18, 2008)

I have a straight blade steel fork. Rides great. Had a curved steel fork at one point and it rode very comfortably. It was definitely "springier" but maybe a tad too springy.

I also have a curved carbon MTB fork and it works great.


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## Mapei (Feb 3, 2004)

When I was shopping for a Colnago back in 2000, Tony, the owner of the bike shop and one of the largest Colnago dealers in the US at the time, demonstrated for me why Colnago uses straight forks.

Whether it was a charlatan's game or not, when Tony bounced the straight-forked Colnago onto the floor, it leaped forward. When he bounced another, curved-fork bicycle onto the floor, that bicycle leaped backward. (Yes, the bicycles had wheels and tires. He wasn't just bouncing the frame on the floor.) Tony went on to say that, just as the straight-forked bicycle leaped forward when bounced, it would do the same while going over bumps in the road, thus making it go down the road better.

In any case, I've discovered that the curve of a fork does not figure very much into overall ride quality. Of my three racing bicycles, the best-riding one by far is the one with the straight fork...a steel Colnago.


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## Kontact (Apr 1, 2011)

Wow - bigtime tinfoil hat thinking!

Straight forks ride no different than curved and are lighter. Lighter sells. 

All steel forks are stiffer than nearly any carbon fork ever made. Steel forks are at the far end of the stiffness scale.

I very much doubt from my own inquiries into carbon production with Enve that a slight curve changes the price one iota. Especially on sleeved forks where the layup is so simple to curve.


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## turbogrover (Jan 1, 2006)

You need to be waaay more specific when you are talking about the engineering of a fork. It isnt just straight or curved. The diameter of the fork legs, the amount of taper, the wall thicknesses, and the materials, all play a factor. Note that many high end builders supply their frames with straight blade carbon forks, because the carbon damps the road vibration better.

Also note that Colnago has designed straight blade steel forks for years with excellent ride quality. Whether the fork is straight or curved is more aesthetic, because it can be designed to be vertically compliant either way.

Back in the day when all forks were made from steel, and the tubing choices were limited, then the curved blade was a way to add compliance to the fork. Nowadays the engineering has advanced to where the curved blade isn't a factor.


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## bigbill (Feb 15, 2005)

I've got both, the Argonaut has a straight Max blade fork and the BLE has a curved Reynolds. My GT has a curved steel as well as my Merckx. The Argonaut was built for the straight fork and it's even a 1 1/8" since a Max blade fork crown was available in oversize.


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## 88 rex (Mar 18, 2008)

Kontact said:


> Wow - bigtime tinfoil hat thinking!
> 
> Straight forks ride no different than curved and are lighter. Lighter sells.
> 
> ...


Steel forks vary greatly. I don't think any one material can put a claim on "stiffness" as any material can be built stiff or weak. As with carbon, a steel fork can be built to ride in a variety of different ways.


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## Kontact (Apr 1, 2011)

88 rex said:


> Steel forks vary greatly. I don't think any one material can put a claim on "stiffness" as any material can be built stiff or weak. As with carbon, a steel fork can be built to ride in a variety of different ways.


Only up to a point. If we are talking about short reach, 43mm rake forks for racing bikes that are made out of similar tubing to a racing frame (531, SL, etc.), they are going to be pretty darn stiff. And that's with fairly thin walls.

You can make a carbon fork just as stiff as a standard steel fork - they are used on disc bikes and tandems all the time. But a production carbon race fork will be made more compliant than any comparable steel fork you can find.


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## Peter P. (Dec 30, 2006)

With carbon forks and the ability to orient the fabric at will, I imagine it's possible to tune the ride characteristics with both straight and curved bladed forks. Since straight forks use less material, I also imagine a greater cost savings.

With steel forks I doubt you can feel the difference between a straight and raked blade. All the flexing going on is farther up the leg, near the crown

If you're interested in a smoother ride, I suggest you experiment with lower tire pressures. In my opinion, most people over inflate their tires considerably.


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## davidka (Dec 12, 2001)

Kontact said:


> Only up to a point. If we are talking about short reach, 43mm rake forks for racing bikes that are made out of similar tubing to a racing frame (531, SL, etc.), they are going to be pretty darn stiff. And that's with fairly thin walls.
> 
> You can make a carbon fork just as stiff as a standard steel fork - they are used on disc bikes and tandems all the time. But a production carbon race fork will be made more compliant than any comparable steel fork you can find.


I have not found this but it's been years since I rode a steel fork (was a custom by John Hollands). I find mostly that the flex or perceived flex difference comes from more flexible fiber/carbon steerer tubes. Trek is even doing a tapered steerer that's wide laterally (for stiffness) but narrow front to back (for compliance). Don't know if it really works or not..



Kontact said:


> Wow - bigtime tinfoil hat thinking!
> 
> Straight forks ride no different than curved and are lighter. Lighter sells.
> 
> ...


There are some forks out there now (Cannondale is notable) that take advantage of trailing dropouts to give more rake to the blades and improve compliance. As a Ti frame lover, I am very happy to see ride compliance making a come back.

To the OP, the best thing you can do to improve ride comfort is go up a tire size and use the best quality tire you can justify the $$ for. 25c tires are as light as 23's were a few years ago. Run them 10psi lower and enjoy a better ride and more roll speed.


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## Kontact (Apr 1, 2011)

davidka said:


> I have not found this but it's been years since I rode a steel fork (was a custom by John Hollands). I find mostly that the flex or perceived flex difference comes from more flexible fiber/carbon steerer tubes. Trek is even doing a tapered steerer that's wide laterally (for stiffness) but narrow front to back (for compliance). Don't know if it really works or not..
> 
> 
> 
> ...


If steerer tubes flexed, headsets would bind and wear out twice as fast. Bigger steerers make for bigger head tubes, and those are stiffer.

Here's an old fork deflection test from before the age of carbon steerers. It is more notable for the location of the steel forks on the chart than how the carbon and aluminum ones compare to each other.

Rinard Fork Deflection Test


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## gordy748 (Feb 11, 2007)

Mr Pegoretti sells his frames with curved forks for a reason...


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## turbogrover (Jan 1, 2006)

gordy748 said:


> Mr Pegoretti sells his frames with curved forks for a reason...


I'm sure Mr Pegoretti has a perfectly legit reason to put curved forks on his bikes. A lot of custom builders still spec curved fork blades.

Modern fork materials don't require all forks to have a curve in the fork blade like the old days. If you like the look of curved fork blades, there are plenty of options available.


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## Cinelli 82220 (Dec 2, 2010)

RoadBoy1 said:


> $50 per fork on lay-up and mold costs by making a carbon fibre fork with straight legs as opposed to one with curved legs


Lay-up cost for a curved fork vs straight fork would be statistically insignificant.
There could be a greater deviation between two models of straight forks, or two models of curved forks, than between all curved forks and all straight forks.

The same would apply to the mold costs.


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## looigi (Nov 24, 2010)

Blades may be straight but no forks are. The front axle is always in front of the axis of the steerer, which means the fork, overall, is bent, so there is a bending moment when force is applied between the two. The straight blades will flex. Engineers can model this precisely and verify it experimentally when designing and testing new designs. They choose materials, construction, shape, and processing to achieve the desired cost, performance, behavior, and style.


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## atpjunkie (Mar 23, 2002)

*from what I heard*



Mapei said:


> When I was shopping for a Colnago back in 2000, Tony, the owner of the bike shop and one of the largest Colnago dealers in the US at the time, demonstrated for me why Colnago uses straight forks.
> 
> Whether it was a charlatan's game or not, when Tony bounced the straight-forked Colnago onto the floor, it leaped forward. When he bounced another, curved-fork bicycle onto the floor, that bicycle leaped backward. (Yes, the bicycles had wheels and tires. He wasn't just bouncing the frame on the floor.) Tony went on to say that, just as the straight-forked bicycle leaped forward when bounced, it would do the same while going over bumps in the road, thus making it go down the road better.
> 
> In any case, I've discovered that the curve of a fork does not figure very much into overall ride quality. Of my three racing bicycles, the best-riding one by far is the one with the straight fork...a steel Colnago.


Mr Colnago went to straight forks because it saved time and money
the rest is all marketing


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## paredown (Oct 18, 2006)

Somewhere in one of the interviews with Ernesto Colnago, he tells the story of the genesis of the straight fork.

It was at the time he was first working with the Ferrari engineers on CF bike frames and components (?Late 80s probably) and they were doing some of the first carbon frames.

The Ferrari engineers asked him why he put the curve in the fork blades--he replied it was for dampening/ride quality, and according to him the Ferrari engineers then proved to his satisfaction that despite years of doing it that way, there was no particular benefit of curved over the straight design that became the Precisa fork, where the rake is set at the top of the blades.

Of course there is the incidental benefit that they are cheaper/easier to make.

(the Ferrari story is mentioned on the Washingmachinepost--but I can't find the original interview...)


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## davidka (Dec 12, 2001)

Kontact said:


> If steerer tubes flexed, headsets would bind and wear out twice as fast. Bigger steerers make for bigger head tubes, and those are stiffer.
> 
> Here's an old fork deflection test from before the age of carbon steerers. It is more notable for the location of the steel forks on the chart than how the carbon and aluminum ones compare to each other.
> 
> Rinard Fork Deflection Test


Being a taller guy (longer steerer), I can assure you, steerer tubes flex quite a bit. If you lock the front brake and rock the bike for/aft (sitting in the seat), you can see flex but more importantly you can also see your brake caliper rocking which indicates flex above the crown.

I know Damon, used to ride with him a bit. Brainy guy for sure. It's worth noting, "All steerer tubes were 1 inch in diameter." so you're using an example of fairly old forks against very new carbon tech. the cross sections in use now are much larger.


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## Kontact (Apr 1, 2011)

davidka said:


> Being a taller guy (longer steerer), I can assure you, steerer tubes flex quite a bit. If you lock the front brake and rock the bike for/aft (sitting in the seat), you can see flex but more importantly you can also see your brake caliper rocking which indicates flex above the crown.
> 
> I know Damon, used to ride with him a bit. Brainy guy for sure. It's worth noting, "All steerer tubes were 1 inch in diameter." so you're using an example of fairly old forks against very new carbon tech. the cross sections in use now are much larger.


The steerer tube is inside the head tube. Where are you seeing the flex? You've just described the crown flexing along with the fork blades, or the entire front end, including the frame flexing.

Larger steerer tubes allow less material to be used in the crown, which increases stiffness in the crown and blades without a weight penalty. They also increase the diameter of the lower crown race, giving the crown a wider surface to push against. But I think you are mistaking the effect - wider crown and headset increasing stiffness - with the cause.


I posted the Rinard test just to demonstrate how monstrously stiff all the steel forks were. All the forks in that test were 1" forks with steel steerers - steerer flex was not a factor with 1" steel tubes.


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## gordy748 (Feb 11, 2007)

*Ah, this is what I was looking for...*



gordy748 said:


> Mr Pegoretti sells his frames with curved forks for a reason...


And here it is. Aesthetics is one reason, the second is that "... flat-crown forks give a little more compliant ride than sloping crowns as the fork legs are slightly longer allowing for better damping characteristics."

The Framebuilders' Collective | Dario Pegoretti – Falz Fork

Of course, I ride a Colnago with a straight fork.


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## davidka (Dec 12, 2001)

Kontact said:


> The steerer tube is inside the head tube. Where are you seeing the flex? You've just described the crown flexing along with the fork blades, or the entire front end, including the frame flexing.
> 
> Larger steerer tubes allow less material to be used in the crown, which increases stiffness in the crown and blades without a weight penalty. They also increase the diameter of the lower crown race, giving the crown a wider surface to push against. But I think you are mistaking the effect - wider crown and headset increasing stiffness - with the cause.


No mistake. Grab your handlebars by the hoods. Rock them from side to side and look at the stem. The stem drives flex down into the steerer which literally bows down it's length inside the head tube. It is very apparent. (ever had a customer complain of creaking in their front end? That can't happen without flex).

Our bearings and interfaces between them and the fork do very little to reinforce against this. First 1-1/8, then tapered 1/5 - 1-1/8 steerer tubes both came along to combat this. It was less of a problem with 1" steel steerers but those have gone extinct in favor of carbon and carbon/glass mixes on higher end bikes which often aren't as stiff.


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## Camilo (Jun 23, 2007)

RoadBoy1 said:


> .... One thing I am noticing and it seems to be tied to the emergence of carbon fibre as a material to make bikes is that just about every fork I see on a carbon bike is a straight blade fork and I am curious about the justification for this...
> 
> ... I can't help but wonder if the advent of carbon fibre forks with straight legs is a thinly veiled attempt by the bike makers to stick it to the consumers and keep their profits high at the same time. ...
> 
> ...


It has nothing to do with cost or ride, and everything to do with aesthetics, pure and simple. Some designers and consumers like straight forks, some like curved. They all have "rake", the difference only being where in the design the rake is, at the bottom or at the top.

I don't doubt there's differences in ride and handling among forks, but it's not because of their curve or lack there of. Ride and handling would be based on how the overall fork was designed.

If you want a better ride, don't look to your fork (or seat post for that matter), but to your tires (FIRST), saddle, shorts, and bar tape. One size larger tire + lower pressure = more comfortable ride and probably faster rolling and faster over all because it's less fatiguing to your body. All the other factors are just so tiny in comparison. OK, the saddle/shorts and bar tape/gloves are also significant, but the tires trump everything.


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## Scooper (Mar 4, 2007)

Dave Kirk had interesting comments on this subject seven years ago in THIS POST. While heading up R&D at Serotta, he conducted laboratory tests of forks with straight blades and with curved blades.

Hint: There were significant differences.


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## SystemShock (Jun 14, 2008)

Scooper said:


> Dave Kirk had interesting comments on this subject seven years ago in THIS POST. While heading up R&D at Serotta, he conducted laboratory tests of forks with straight blades and with curved blades.
> 
> Hint: There were significant differences.


Interesting... and I do respect Dave Kirk very much as a framebuilder and R&D guy.

Thank you for posting the link.
.


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## Kontact (Apr 1, 2011)

Scooper said:


> Dave Kirk had interesting comments on this subject seven years ago in THIS POST. While heading up R&D at Serotta, he conducted laboratory tests of forks with straight blades and with curved blades.
> 
> Hint: There were significant differences.


It should be noted that Dave was building steel forks, all with the same blade tubing. The direct applications of a steel fork test to forks of all materials and all wall thicknesses is pretty questionable.


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## Scooper (Mar 4, 2007)

Kontact said:


> It should be noted that Dave was building steel forks, all with the same blade tubing. The direct applications of a steel fork test to forks of all materials and all wall thicknesses is pretty questionable.


Agreed. This was apples to apples. As I understand it, the only difference between the forks was that one had straight blades with the offset built into the crown, while the other fork had curved blades. Everything else was the same, so any difference in compliance was related only to whether the blades were straight or curved.


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## DY123 (Oct 5, 2006)

If you want to soften up your ride try changing your tires.

Moving from a 23 to a 25 or 28 would do much more to affect ride softness than the difference between a straight blade and a curved blade would.


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## bigbill (Feb 15, 2005)

DY123 said:


> If you want to soften up your ride try changing your tires.
> 
> Moving from a 23 to a 25 or 28 would do much more to affect ride softness than the difference between a straight blade and a curved blade would.


Yup, my only regret on the Argonaut is that the fork won't clear a 25. My Nobilette GT could easily fit a 28 (if it clears the brakes).


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## turbogrover (Jan 1, 2006)

Scooper said:


> Dave Kirk had interesting comments on this subject seven years ago in THIS POST. While heading up R&D at Serotta, he conducted laboratory tests of forks with straight blades and with curved blades.
> 
> Hint: There were significant differences.


so, your point is that if you test the same fork tubing, the set that is curved will offer better compliance? Of course it will be. Fortunately, fork tubing is available in an infinite variety, and curved blades are no longer a necessary design requirement.


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## SystemShock (Jun 14, 2008)

Scooper said:


> Agreed. This was apples to apples. As I understand it, the only difference between the forks was that one had straight blades with the offset built into the crown, while the other fork had curved blades. Everything else was the same, so any difference in compliance was related only to whether the blades were straight or curved.


Yup... via the scientific method, this would be exactly what you want. Isolate one variable, while making sure everything else was the same.

If Kirk hadn't done that, then folks would be complaining that the results were invalid, owing to poor methodology.
.


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## Kontact (Apr 1, 2011)

SystemShock said:


> Yup... via the scientific method, this would be exactly what you want. Isolate one variable, while making sure everything else was the same.
> 
> If Kirk hadn't done that, then folks would be complaining that the results were invalid, owing to poor methodology.
> .


Well, it's the start of scientific method. But it only answers one question, without suggesting the answers the real questions about the relationship between curves and other modifications.

The real answer might be that you have to curve the fork if you want heavy blades to ride like thin walled, straight blades.

There is absolutely nothing wrong with curved blades, but one could view curved blades as a method for making due with limited materials, as well as an easier method for customizing rake. With modern production techniques and materials, it is probably unnecessary. I think curved seat stays, which no one really makes a big deal about, is about the same level of necessity.


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## velodog (Sep 26, 2007)

atpjunkie said:


> Mr Colnago went to straight forks because it saved time and money
> the rest is all marketing


Thank You.


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## tarwheel2 (Jul 7, 2005)

Kontact said:


> Wow - bigtime tinfoil hat thinking!
> 
> Straight forks ride no different than curved and are lighter. Lighter sells.
> 
> ...


Dude, what are you smoking? Your statements are misinformed. Whether a fork is stiff or not depends on its design, not whether it's made of steel or carbon. It also doesn't matter if the fork is straight or curved.

The nicest riding fork I ever had on a bike was a chrome steel GIOS fork. I bought the GIOS to replace a Bianchi with a carbon fork, and the Bianchi was the most uncomfortable riding bike I have ever owned. The front end was like a jackhammer compared to the GIOS. My Eddy Merckx Corsa 01, also had a chome steel fork that was relatively stiff but not uncomfortable. I have also owned bikes with carbon forks that were very comfortable. It's all in the design.


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## Kontact (Apr 1, 2011)

tarwheel2 said:


> Dude, what are you smoking? Your statements are misinformed. Whether a fork is stiff or not depends on its design, not whether it's made of steel or carbon. It also doesn't matter if the fork is straight or curved.
> 
> The nicest riding fork I ever had on a bike was a chrome steel GIOS fork. I bought the GIOS to replace a Bianchi with a carbon fork, and the Bianchi was the most uncomfortable riding bike I have ever owned. The front end was like a jackhammer compared to the GIOS. My Eddy Merckx Corsa 01, also had a chome steel fork that was relatively stiff but not uncomfortable. I have also owned bikes with carbon forks that were very comfortable. It's all in the design.


I might ask you the same. You posted about the same as what I did: That the curve of the fork is just a design feature, not a make or break necessity that determines ride quality. Ride quality comes from the whole fork, not just whether it is curved or not.


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## gordy748 (Feb 11, 2007)

Umm, I think those guys attacking Kirk's test need to bear in mind that the test found a simple result. All else being equal, curved forks are preferred by riders.

Given that there are a lot of materials, and types of materials, for forks, it's equally clear that a $500 Enve straight fork is going to be superior to a $50 Walmart special. That said, a straight tube is cheaper to make than a curved tube, irrespective of material.

Don't forget that the fork is only part of the bicycle's front end. Geometry, rake, trail, etc all work together to deliver a handling style that is more important than the curvature of the forks.

So the conclusion is that [curved fork] = [slightly better ride] + [good bit more expensive]. I guess this is why Pinarello's wacky forks are so good.


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## Kontact (Apr 1, 2011)

gordy748 said:


> Umm, I think those guys attacking Kirk's test need to bear in mind that the test found a simple result. All else being equal, curved forks are preferred by riders.
> 
> Given that there are a lot of materials, and types of materials, for forks, it's equally clear that a $500 Enve straight fork is going to be superior to a $50 Walmart special. That said, a straight tube is cheaper to make than a curved tube, irrespective of material.
> 
> ...


No one attacked Kirk's test. No one doubted his methods, results or anything else. I know Dave a little bit, and he'd agree with everything posted about the conclusions that can or can't be drawn from his test using the same blades to build different forks.


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## kapu902 (Apr 7, 2010)

I think the original logic was that a force on the end of a straight piece of material will cause the material to curve. (Take a wooden ruler. Put it in a vice. Apply force to the free end. It makes a curve.). If you want to counteract that curve just pre-bend it the opposite way and your fork will resist bending plus you will have built in a rake as well which makes it more stable.


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## turbogrover (Jan 1, 2006)

kapu902 said:


> I think the original logic was that a force on the end of a straight piece of material will cause the material to curve. (Take a wooden ruler. Put it in a vice. Apply force to the free end. It makes a curve.). If you want to counteract that curve just pre-bend it the opposite way and your fork will resist bending plus you will have built in a rake as well which makes it more stable.


:confused5: 
Whaa?


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