Bent and straight forks
I have this wonderful classic, retro Colnago (Columbus SL tubing) with all Campagnolo except for the handlebar (Cinelli) and saddle (Titaníum 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 |
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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Originally Posted by gthomson
(Post 22557687)
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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Curved forks provided a little more flex to dampen a harsh ride. They also look way better than straight forks.
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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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Originally Posted by gearbasher
(Post 22557721)
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.
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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. |
Originally Posted by bamboobike4
(Post 22557751)
....
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. 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 |
Originally Posted by gthomson
(Post 22557687)
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? :)
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?? https://live.staticflickr.com/1722/4...8ef101_c_d.jpg Steve in Peoria |
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?
https://cimg3.ibsrv.net/gimg/bikefor...2b2fdda9ec.jpg |
Originally Posted by gthomson
(Post 22558344)
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?
https://cimg3.ibsrv.net/gimg/bikefor...2b2fdda9ec.jpg |
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I've got the one with strait forks. Rodriguez Arrow with the strait and threadless 1" options.
https://cimg9.ibsrv.net/gimg/bikefor...3747cacb5f.jpg |
Originally Posted by bamboobike4
(Post 22557751)
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. 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. |
Originally Posted by DiabloScott
(Post 22558458)
...
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. Steve in Peoria |
I’ve had this bike set up with a straight blade carbon fork and a curved blade steel fork:
https://cimg6.ibsrv.net/gimg/bikefor...67df28931.jpeg https://cimg4.ibsrv.net/gimg/bikefor...9bc46085a.jpeg In terms of ride quality, I really couldn’t feel a difference. |
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. ... |
Originally Posted by joesch
(Post 22558543)
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. ... |
Originally Posted by smd4
(Post 22558558)
Well, at least this isn’t biased.:rolleyes:
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 |
I guess when I first saw them at a bike trade show, they did stand out as being very different.
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Originally Posted by steelbikeguy
(Post 22558498)
can you share the data behind these assertions?
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. |
Originally Posted by nlerner
(Post 22558536)
I’ve had this bike set up with a straight blade carbon fork and a curved blade steel fork:
https://cimg6.ibsrv.net/gimg/bikefor...67df28931.jpeg https://cimg4.ibsrv.net/gimg/bikefor...9bc46085a.jpeg In terms of ride quality, I really couldn’t feel a difference. Maybe those wheels absorb soo much shock that it hides the fork diff? |
Originally Posted by joesch
(Post 22558696)
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? |
Originally Posted by joesch
(Post 22558543)
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 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. ... |
Originally Posted by nlerner
(Post 22558832)
Could be the wheels/tires. Or could be I’m oblivious to feeling the difference. As they say, ymmv.
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