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Bent and straight forks

Old 06-29-22, 06:05 AM
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petercph
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Bent and straight forks

I have this wonderful classic, retro Colnago (Columbus SL tubing) with all Campagnolo except for the handlebar (Cinelli) and saddle (TitanŪum Flite (if that is a brand?) that I so love to ride. I bought it back in '91 or '92.
It has the slightly bent fork but I seem to remember the straight forks began to show around that time or perhaps the year after I acquired mine. Does anybody know when frame builders and bike builders began to equip their bikes with straight forks, and when this new trend sort of took over?

Thanks

Peter
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Old 06-29-22, 06:54 AM
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Good question and what was the reason behind bending the front fork on steel bikes? I keep looking at my old bikes and wondering, am I starting to bend it more as I age and gain weight?
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Old 06-29-22, 06:58 AM
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Originally Posted by gthomson View Post
Good question and what was the reason behind bending the front fork on steel bikes? I keep looking at my old bikes and wondering, am I starting to bend it more as I age and gain weight?
Probably to make it a little less hard to ride
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Old 06-29-22, 07:14 AM
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Curved forks provided a little more flex to dampen a harsh ride. They also look way better than straight forks.
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Old 06-29-22, 07:24 AM
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Looking at old Colnago catalogues, in '88 the forks on all models were still raked. In '89 there was a mix of straight and raked forks, depending on model.
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Old 06-29-22, 07:32 AM
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Originally Posted by gearbasher View Post
Looking at old Colnago catalogues. In '88 the forks were still raked. In '89 there was a mix of straight and raked forks, depending on model.
OK, so I assume it must have been around '90 we began to see them i greater number - I just googled Liege-Bastogne-Liege 1993 and 1994 and 1995 and the riders still used the bent foks there - so maybe the straight forks took over mid/late 90'es
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Old 06-29-22, 07:47 AM
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The straight Colnago forks have the same rake angle as the curved ones did.
The angled crown serves the geometric purpose of the curved fork as far as placing the axle.

I have 2 with curved forks (1985) and 2 with straight forks. (2003, 2016)
All are steel, so between 1985 and 2003. Only 15 years to narrow down.
(I'm bad at math).

One straight steel was swapped in for the straight carbon, only because I needed more steerer height.
I believe they are called Precisa forks, not sure if there are other models. There are in carbon.

There are too many other variables for me to give any anecdotal insight.
Wheels, frame geometry, frame size, headset, bars, stem, etc etc.

There is a certain % of the bike/rider weight that acts on the fork, between the headset and the axle.
How that weight is distributed over a curved distance vs. a straight distance would appear to be the difference?
How much weight does it take to flex that fork, of that material, over that distance?
What other forces then act, as far as descending, cornering, climbing, braking?

I don't know. Steve in Peoria might.
He be an engineer. I are not.

A lot of cycling preferences are psychological.
When I only dreamed of owning a Colnago, I thought the straight forks were a silly gimmick.
Let's just say that's changed. I still don't think that much about them, but they're fine.

Like others here, I either like, feel, or imagine the flex of a nice steel fork, and prefer the comfort.

Last edited by bamboobike4; 06-29-22 at 07:56 AM.
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Old 06-29-22, 02:06 PM
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Originally Posted by bamboobike4 View Post
....

I don't know. Steve in Peoria might.
He be an engineer. I are not.

A lot of cycling preferences are psychological.
When I only dreamed of owning a Colnago, I thought the straight forks were a silly gimmick.
Let's just say that's changed. I still don't think that much about them, but they're fine.

Like others here, I either like, feel, or imagine the flex of a nice steel fork, and prefer the comfort.
I appreciate the vote of confidence, but as an electrical engineer, I'll defer to those who have actual knowledge of the data.
However, I do support the use of data and experiments and tests, as opposed to opinions based on limited experience with a piece of equipment.

One of my projects that is still waiting for time and attention is to be able to measure fork flex while riding. Until that happens, the next best thing is for someone with a good workshop to hang weights off of a range of forks and measure how much they deflect. Gugie? Bulgie? Anyone want to volunteer?

Steve in Peoria
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Old 06-29-22, 02:15 PM
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Originally Posted by gthomson View Post
Good question and what was the reason behind bending the front fork on steel bikes? I keep looking at my old bikes and wondering, am I starting to bend it more as I age and gain weight?
my guess is that bike tubes were always created as straight tubes, and fork blades were just modified tubes that were tapered and possibly drawn to be thinner walls towards the dropout end. I suspect that it was easier to let everyone rake the fork blades themselves as opposed to making fork crowns with specific angles for straight blades.

Of course, lugs are made for specific angles, so making fork crowns for various angles wasn't a big conceptual or technical leap. To some degree, coming up with innovation is part technical and part marketing. Companies have played around with variations in tube shapes and bends for a long time, and always claimed some benefit. Whether they do or not.. well, there's usually not much evidence available. Still, they look kinda cool.

The Bates with the Diadrant fork is a great example. If one bend is good, then two bends must be twice as good??



Steve in Peoria
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Old 06-29-22, 02:54 PM
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So still on the topic of bends but moving away from front forks, a friend sent me this picture asking if this was real or a hack? What would have been the purpose of adding this bend to the top tube?
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Old 06-29-22, 03:22 PM
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Originally Posted by gthomson View Post
So still on the topic of bends but moving away from front forks, a friend sent me this picture asking if this was real or a hack? What would have been the purpose of adding this bend to the top tube?
To make a small frame for a short person.
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Old 06-29-22, 04:20 PM
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And then there's Hetchins:

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Old 06-29-22, 04:29 PM
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I've got the one with strait forks. Rodriguez Arrow with the strait and threadless 1" options.
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Old 06-29-22, 04:38 PM
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Originally Posted by bamboobike4 View Post
The straight Colnago forks have the same rake angle as the curved ones did.
The angled crown serves the geometric purpose of the curved fork as far as placing the axle.
Right, except rake is not an angle, it's a linear measurement (millimeters, not degrees).

A straight fork and a bent fork will respond somewhat differently to a hard hit - like a pot hole or a curb jump.
A bent fork will absorb some of that hit by flexing, and the strength of the material dampens the shock and reduces the force transferred to the headset.
A straight fork might absorb some of the hit, but not by flexing, and much more of the force will be transferred to the headset.
Carbon fiber doesn't like bending/flexing stresses so bent forks are a lot less common than straight ones... probably heavier too.
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Old 06-29-22, 05:21 PM
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Originally Posted by DiabloScott View Post
...
A straight fork and a bent fork will respond somewhat differently to a hard hit - like a pot hole or a curb jump.
A bent fork will absorb some of that hit by flexing, and the strength of the material dampens the shock and reduces the force transferred to the headset.
A straight fork might absorb some of the hit, but not by flexing, and much more of the force will be transferred to the headset.
Carbon fiber doesn't like bending/flexing stresses so bent forks are a lot less common than straight ones... probably heavier too.
can you share the data behind these assertions?

Steve in Peoria
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Old 06-29-22, 06:24 PM
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I’ve had this bike set up with a straight blade carbon fork and a curved blade steel fork:





In terms of ride quality, I really couldn’t feel a difference.
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Old 06-29-22, 06:33 PM
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This should answer most of the questions especially re: colnago precisa fork history

https://cycling-obsession.com/colnag...-fork-history/

The introduction of the straight-blade fork is an important moment in the history of Colnago’s bike production. It was a turning point that led the entire cycling industry into a new era. The Precisa straight leg fork first appears in their 1989 catalog, but is still manufactured today and supplied with modern Colnago Master and Arabesque steel frames. ... A fork with straight blades can guarantee exceptional results, far superior to forks with curved blades. ...

Last edited by joesch; 06-29-22 at 06:36 PM.
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Old 06-29-22, 06:49 PM
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Originally Posted by joesch View Post

The introduction of the straight-blade fork is an important moment in the history of Colnagoís bike production. It was a turning point that led the entire cycling industry into a new era. The Precisa straight leg fork first appears in their 1989 catalog, but is still manufactured today and supplied with modern Colnago Master and Arabesque steel frames. ... A fork with straight blades can guarantee exceptional results, far superior to forks with curved blades. ...
Well, at least this isnít biased.
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Old 06-29-22, 08:14 PM
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Originally Posted by smd4 View Post
Well, at least this isnít biased.
I think the term for it is "marketing".

Colnago was (imho) really good at gimmicks as a marketing and sales tool. The interesting thing to me is that they were also pretty darned nice and popular bikes with a good race history. ... although I'm not sure if the Bi-titan was considered a success....

In any case, their gimmicks weren't detrimental, and certainly got the public's attention. I imagine that most folks were pretty happy with their Colnagos, regardless of whether it offered measurably better performance.

Perhaps this is a good time to state that I have a Hetchins with curly stays. I don't think the stays make a difference in the ride, but are interesting. The bike itself does ride nicely, and I can only guess that it is due to the Reynolds 531C tubing being a lighter gauge than the 531 used on my nominally similar Raleigh International. The Hetchins has rounder fork blades too, which should offer more flex fore and aft.

Steve in Peoria
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Old 06-29-22, 08:18 PM
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I guess when I first saw them at a bike trade show, they did stand out as being very different.
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Old 06-29-22, 09:18 PM
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Originally Posted by steelbikeguy View Post
can you share the data behind these assertions?
An electrical engineer wouldn't understand

I'm obviously extrapolating on real world design results from recognized material properties; strength and rigidity.
Certainly you know CF's advantage is in strength to weight ratio and rigidity - it barely flexes at all, even it it's curved.
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Old 06-29-22, 09:38 PM
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Originally Posted by nlerner View Post
Iíve had this bike set up with a straight blade carbon fork and a curved blade steel fork:





In terms of ride quality, I really couldnít feel a difference.
Thats surprising to me as I can for sure feel the diff between CF and steel forks.
Maybe those wheels absorb soo much shock that it hides the fork diff?
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Old 06-30-22, 04:46 AM
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Originally Posted by joesch View Post
Thats surprising to me as I can for sure feel the diff between CF and steel forks.
Maybe those wheels absorb soo much shock that it hides the fork diff?
Could be the wheels/tires. Or could be Iím oblivious to feeling the difference. As they say, ymmv.
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Old 06-30-22, 06:25 AM
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Originally Posted by joesch View Post
This should answer most of the questions especially re: colnago precisa fork history

(There was a link here, that i needed to delete, because am not allowed to include the link in my reply because I have not made enough posts!!!! )

The introduction of the straight-blade fork is an important moment in the history of Colnagoís bike production. It was a turning point that led the entire cycling industry into a new era. The Precisa straight leg fork first appears in their 1989 catalog, but is still manufactured today and supplied with modern Colnago Master and Arabesque steel frames. ... A fork with straight blades can guarantee exceptional results, far superior to forks with curved blades. ...
Excellent. This answers my initial question. Great link! Thank you so much. And I see the thread has already moved on to new adventures :-)
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Old 06-30-22, 07:00 AM
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Originally Posted by nlerner View Post
Could be the wheels/tires. Or could be Iím oblivious to feeling the difference. As they say, ymmv.
Don't feel bad if you're oblivious. They say "ignorance is bliss". Then I must be happiest person on the face of the earth. I rode with a guy who wouldn't patch his tubes because he said he could feel the patches while riding. Also, we once stopped because he had to raise his saddle. He raised it about the thickness of a human hair, gets on the bike and said: "much better". I don't know if he lived like the "Princess and the Pea" or I'm totally oblivious.
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