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  1. #1
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    Question on Carbon Forks

    One of the reasons I hear from people on why they choose carbon for bike frames, is stiffness of carbon fiber. Most road forks I see these days are carbon fiber and also straight, with virtually no taper, as compared to steel forks of the past that had some rake (curve at the end) to them and were thinner towards the dropout. The rake and tapered design was to allow some flex in the fork to absorb road shock.

    My question is how much road shock is transmitted to the rider through carbon forks as compared to raked, tapered steel forks? Will I need extra padding in my bar tape? I do not advocate wet spaghetti for forks, but I am wondering about the feel of these forks.

  2. #2
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    There is no answer to your question. Like steel forks, knowing what they are made of doesn't say how they ride.

  3. #3
    'brifter' is a lame word.
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    The shape of the fork leg (curved or straight) has little to do w/ how it absorbs rock shock. As for your question...no one here can answer it.
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  4. #4
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    Classic steel road forks are about as stiff and punishing as forks commonly get, though some carbon forks can be close.

    This article is old, but the cluster of steel forks at the extreme of minimum deflection compared to every carbon and aluminum fork at that time should be illustrative:

    https://www.sheldonbrown.com/rinard/..._forktest.html



    The Tange Silhouette shows that steel can be made a bit softer, but most steel forks are going to be the least soft riding forks for both deflection and vibration damping.
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  5. #5
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    For what it’s worth: most carbon forks today are NOT straight - they do have rake, usually 40 to 45mm

    They look straighter because of their design, but if you look closely you can see clearly that the fork does not extend along the same angle as the head tube. It’s just deceptive because instead of going out straight and then turning lower down, the rake angle starts immediately at the bottom of the head tube.

  6. #6
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    Quote Originally Posted by fronesis View Post
    For what it’s worth: most carbon forks today are NOT straight - they do have rake, usually 40 to 45mm

    They look straighter because of their design, but if you look closely you can see clearly that the fork does not extend along the same angle as the head tube. It’s just deceptive because instead of going out straight and then turning lower down, the rake angle starts immediately at the bottom of the head tube.
    That is generally not what is meant by straight vs curved fork blades. Straight refers to the blades, not the whole fork.
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    Quote Originally Posted by Kontact View Post
    That is generally not what is meant by straight vs curved fork blades. Straight refers to the blades, not the whole fork.
    Fair enough. But I was replying to the OP, who wrote this:

    Most road forks I see these days are carbon fiber and also straight, with virtually no taper, as compared to steel forks of the past that had some rake
    I therefore took him to be suggesting that carbon forks have no rake.

    I had also thought, but maybe I was wrong, that the whole point of the curve in a steel fork was to create the needed rake. But maybe steel forks were curved for some other reason that I don’t understand.

  8. #8
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    Quote Originally Posted by fronesis View Post
    Fair enough. But I was replying to the OP, who wrote this:



    I therefore took him to be suggesting that carbon forks have no rake.

    I had also thought, but maybe I was wrong, that the whole point of the curve in a steel fork was to create the needed rake. But maybe steel forks were curved for some other reason that I don’t understand.
    Curved fork blades go all the way back to early bikes. I would imagine that early forks were likely less likely to fail at the crown if the blades where pre-bent to get the flex to occur away from the highest stress areas. The later fork materials were reliable enough to not need this hedge.
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  9. #9
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    First and foremost, your tires will have more to do with the quality of your ride than anything else on the bike. There is a very good reason Mr. Dunlop invented the pneumatic tire 130 years ago which we still use today:

    https://en.wikipedia.org/wiki/John_Boyd_Dunlop

    They act as mini shock absorbers better than any other part of the bike except your own body.

    My best guess as to why carbon appears to be the material of choice for forks on both aluminum and steel bikes is the advent of disc brakes. Because of the extra stresses during braking with disc brakes, forks have to be beefier than on older rim brake bikes. If you did this to a steel or aluminum fork, it would add significant weight and would not be marketable in the weight obsessed road biking culture.
    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein

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    Quote Originally Posted by Kontact View Post
    Curved fork blades go all the way back to early bikes. I would imagine that early forks were likely less likely to fail at the crown if the blades where pre-bent to get the flex to occur away from the highest stress areas. The later fork materials were reliable enough to not need this hedge.
    Makes sense.

    Quote Originally Posted by Lombard
    My best guess as to why carbon appears to be the material of choice for forks on both aluminum and steel bikes is the advent of disc brakes.
    I think the switch to carbon forks pre-dates the massive switch to disc brakes, and I think the explanation is weight. A fully cro-mo road fork weighs around 1,000 grams – that's MORE than a light aluminum or carbon FRAME. Today's full carbon road forks can weigh as little as 300 grams.

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    Quote Originally Posted by cxwrench View Post
    The shape of the fork leg (curved or straight) has little to do w/ how it absorbs rock shock. As for your question...no one here can answer it.
    Correction: The shape of the fork leg (curved or straight) has NOTHING to do w/ how it absorbs rock shock.

  12. #12
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    Quote Originally Posted by fronesis View Post
    I think the switch to carbon forks pre-dates the massive switch to disc brakes, and I think the explanation is weight. A fully cro-mo road fork weighs around 1,000 grams – that's MORE than a light aluminum or carbon FRAME. Today's full carbon road forks can weigh as little as 300 grams.
    You are correct about carbon forks on non-carbon bike frames predating disc brakes. However, aluminum and cro-mo forks were still common until disc brakes came on the scene for the reasons I stated that disc brake bikes need a beefier fork. Imagine how much a cro-mo fork designed to be strong enough for a disc brake bike would weigh. I don't know that one exists.
    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein

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    ^ There are lots of steel disc forks out there. They're plenty strong, and as far as I know, don't weigh any more than the rim brake steel forks. Carbon forks are more popular now because they're significantly lighter and not a whole lot more expensive.

    When it comes to ride quality, like has been said, material has little to do with it. I have a very comfortable and compliant carbon road fork, and I have a quite stiff and uncomfortable carbon road fork.

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    Quote Originally Posted by Pisgah2000 View Post
    ^ There are lots of steel disc forks out there. They're plenty strong, and as far as I know, don't weigh any more than the rim brake steel forks. Carbon forks are more popular now because they're significantly lighter and not a whole lot more expensive.
    .
    Steel disc is going to weigh more than rim if only as there's more material for the disc mounting tabs, as well as they generally beef up the fork to accommodate different braking forces at the hub. No idea how much more it weighs and since it's steel with a likely steel frame, I doubt it matters much as you're generally not counting grams at that point.

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    Quote Originally Posted by Lombard View Post
    First and foremost, your tires will have more to do with the quality of your ride than anything else on the bike. There is a very good reason Mr. Dunlop invented the pneumatic tire 130 years ago which we still use today:

    https://en.wikipedia.org/wiki/John_Boyd_Dunlop

    They act as mini shock absorbers better than any other part of the bike except your own body.

    My best guess as to why carbon appears to be the material of choice for forks on both aluminum and steel bikes is the advent of disc brakes. Because of the extra stresses during braking with disc brakes, forks have to be beefier than on older rim brake bikes. If you did this to a steel or aluminum fork, it would add significant weight and would not be marketable in the weight obsessed road biking culture.
    Nope. Carbon forks where common for decades before disc brakes, and disc forks are commonly steel and aluminum. Disc carbon forks are heavier than carbon rim brake forks.
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  16. #16
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    Seems to me that carbon forks became common in the mid to late 90s (about the time 9 speed came out). Way before disc brakes.

  17. #17
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    Quote Originally Posted by Pisgah2000 View Post
    When it comes to ride quality, like has been said, material has little to do with it. I have a very comfortable and compliant carbon road fork, and I have a quite stiff and uncomfortable carbon road fork.
    Likewise, I have two different carbon road bikes. One is laterally stiff, the other one feels like a noodle.
    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein

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  18. #18
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    Quote Originally Posted by crit_boy View Post
    Seems to me that carbon forks became common in the mid to late 90s (about the time 9 speed came out). Way before disc brakes.
    Kestrel introduced the EMS carbon fork in 1989, but it took a few years before other companies started offering it on their bikes. It pops up as an option in the 1994 Litespeed catalog. They probably would have caught on earlier, but the SR Prism aluminum fork came out about the same time and was about the same weight and less costly. So it was the mid-90s before most folks came across them.
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  19. #19
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    Looking at listings for disk and regular forks on weightweenies, I'd say the weight penalty to add discs is very similar for carbon, steel and aluminum forks.
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  20. #20
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    Let's be real here. Most people ride carbon bikes because they were told that carbon is the best and because the pros ride it. As for forks, most bikes come with carbon forks, a steel fork can have the same ride quality, but it will weigh a bit more. That's just simple logic. Kerry Irons is right though. The shape of the fork leg (curved or straight) has NOTHING to do w/ how it absorbs rock shock.

  21. #21
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    Quote Originally Posted by Kontact View Post
    Kestrel introduced the EMS carbon fork in 1989, but it took a few years before other companies started offering it on their bikes. It pops up as an option in the 1994 Litespeed catalog. They probably would have caught on earlier, but the SR Prism aluminum fork came out about the same time and was about the same weight and less costly. So it was the mid-90s before most folks came across them.
    I remember that fork! It was actually a nice fork.

  22. #22
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    Quote Originally Posted by terbennett View Post
    Let's be real here. Most people ride carbon bikes because they were told that carbon is the best and because the pros ride it. As for forks, most bikes come with carbon forks, a steel fork can have the same ride quality, but it will weigh a bit more. That's just simple logic. Kerry Irons is right though. The shape of the fork leg (curved or straight) has NOTHING to do w/ how it absorbs rock shock.
    I don't see the logic in claiming that steel forks ride as softly as the alternatives when it isn't true.
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  23. #23
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    Quote Originally Posted by Kontact View Post
    I don't see the logic in claiming that steel forks ride as softly as the alternatives when it isn't true.

    I still believe it a steel can be compliant and ride as softly as the alternatives...except maybe carbon.
    The Rinard Fork Deflection Test

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