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    Senior Member zeppinger's Avatar
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    Curved vs. Straight forks?

    What are the advantages and disadvantages of a curved vs. a straight fork? I understand the argument for lugged vs. unlugged but I think straight forks just look bad. Are they better for some reason? I am having a hard time choosinng a new credit card tourer and most all of the bikes I look at have straight forks! Surly Pacer for the win?

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    I suppose the straight ones have just a bit less material for a marginal weight saving. Curved has the advantage that you can more easily see if the fork was bent after an impact. Normally the bend would occur right at the fork crown and sighting down the headtube with a curved fork will clearly reveal if the fork continues straight at that point before bending forward gradually or if it's bent back.

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    Senior Member z415's Avatar
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    Wheelbase considerations. IIRC, a longer wheelbase, generally from a curved fork, means a more stable ride. To be frank, I am very tired and I cannot remember the pros and cons of each. I know that I would prefer a smaller wheelbase for my road bike and larger for a tourer or anything for the long haul.
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    Quote Originally Posted by z415 View Post
    Wheelbase considerations. IIRC, a longer wheelbase, generally from a curved fork, means a more stable ride. To be frank, I am very tired and I cannot remember the pros and cons of each. I know that I would prefer a smaller wheelbase for my road bike and larger for a tourer or anything for the long haul.
    Steering geometry (wheelbase, rake, trail, etc.) is independent of whether the fork is curved or straight.
    If you look at a bike with a straight fork, e.g.:

    you can see that the front wheel axle is still located forward of where it would be if the fork were a direct extension of the head tube. So you can get between the fork crown and any chosen position for the front axle with either a straight fork design or a curved one.

    And the positive forward rake (whether by using a curve or a straight fork with an angle at the crown) is designed to *reduce* stability, not to enhance it. Bicycles built for extreme stability, such as used for motor-paced speed records, use a reversed fork design with negative rake and are designed for straight-line riding. But for normal riding a bike is designed with some positive rake to reduce stability and make for easier turning.

  5. #5
    Super Moderator Allen's Avatar
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    Straight forks are not typically tapered and are used with disk brakes. Fork rake is determined by the offset of the crown. Forks of different rakes have to built with different crowns.

    Curved forks are tapered, not suitable for disks. A builder can keep a single style of crown in stock and build forks for various geometry bikes since the rake comes from the curve.

    Basically, straight forks are for disks, cured forks are for all the rest of the kinds of brakes.

  6. #6
    Senior Member z415's Avatar
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    Quote Originally Posted by prathmann View Post
    Steering geometry (wheelbase, rake, trail, etc.) is independent of whether the fork is curved or straight.
    If you look at a bike with a straight fork, e.g.:

    you can see that the front wheel axle is still located forward of where it would be if the fork were a direct extension of the head tube. So you can get between the fork crown and any chosen position for the front axle with either a straight fork design or a curved one.

    And the positive forward rake (whether by using a curve or a straight fork with an angle at the crown) is designed to *reduce* stability, not to enhance it. Bicycles built for extreme stability, such as used for motor-paced speed records, use a reversed fork design with negative rake and are designed for straight-line riding. But for normal riding a bike is designed with some positive rake to reduce stability and make for easier turning.
    Back when I was shopping around for forks, generally (not always) curved forks led to longer wheelbases, so I would say it is not 100% independent, though that could just be predominant in my perspective market of cheaper forks.

    And yea, you're right, got the whole stability thing reversed. Didn't believe you so I went for a ride. After that my brain clicked. Track bikes, DH bikes and their geometry.

    Off to bed.
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  7. #7
    Touring - loving it!!! mylesau's Avatar
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    The main reason to go for 'curved' forks is shock absorption - they take the 'hum' out of the road - straight forks tend to send the 'hum' to your hands.

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    Senior Member zeppinger's Avatar
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    Quote Originally Posted by mylesau View Post
    The main reason to go for 'curved' forks is shock absorption - they take the 'hum' out of the road - straight forks tend to send the 'hum' to your hands.
    This was my understanding as well but I was not sure how important it was. Mainly I like the the aesthetics of it but that because I like the look of older lugged steel bikes. Maybe I should just buy used!

    Are there any other reasons for the curved fork that I should know about or advantages of a straight blade?

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    straight forks tend to be stiffer vertically, think about how easy it is to bend a straw sideways, versus trying to crush it end-end... does that make sense? the more bend in a fork (generally speaking) the more springy it will be.

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    Professional Fuss-Budget Bacciagalupe's Avatar
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    Quote Originally Posted by positron View Post
    straight forks tend to be stiffer vertically, think about how easy it is to bend a straw sideways, versus trying to crush it end-end... does that make sense?
    Not really, because vertical compliance can also be affected by tube stiffness, tube thickness, tube shapes, crown design, angles of impact, choice of material and numerous non-fork-related factors (e.g. tire pressure and width).

    Maybe in the early days it was more difficult to make a compliant fork without curving it, but I doubt that is still the case, especially with CF forks.

  11. #11
    cyclopath vik's Avatar
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    Quote Originally Posted by mylesau View Post
    The main reason to go for 'curved' forks is shock absorption - they take the 'hum' out of the road - straight forks tend to send the 'hum' to your hands.
    +1 - before there was suspension in bicycles folks used high volume tires and curved forks to deal with the inevitable shock and vibration from the road.

    I have touring bikes with straight forks [all disc brake bikes] and curved forks [all v-brake bikes] the curved forks do provide a more compliant ride and make hand numbness and other related issues considerably less of a concern. You can mitigate these problems on a straight fork bike by using more padding, different grips, better gloves, higher volume tires, etc... Unless you are very susceptible to these types of injuries in which case I'd stick with a nice compliant curved steel fork on your touring rig.

    Unless I need disc brakes for a specific application I'd prefer a curved fork and v-brakes for touring. I'd say I'm about in the middle of the pack when it comes to how sensitive my hands are to injury. I have had a nerve injury that lasted for 6 months on a bike with straight forks on a very rough road and I know the transmission of vibration straight up those stiff fork legs to my bars was a significant factor in my injury. I've since added Ergon grips and double layers of cork tape to those bars. I definitely don't want a repeat injury given how long it took to heal.
    Last edited by vik; 09-22-09 at 09:45 AM.
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    Quote Originally Posted by Bacciagalupe View Post
    Not really, because vertical compliance can also be affected by tube stiffness, tube thickness, tube shapes, crown design, angles of impact, choice of material and numerous non-fork-related factors (e.g. tire pressure and width).

    Maybe in the early days it was more difficult to make a compliant fork without curving it, but I doubt that is still the case, especially with CF forks.
    Ok, I was definitely over simplifying it, but: given two identical steel fork tubes, one curved along its length, one completely straight and mounted in an offset-producing crown. Assuming the same offset, trail etc. The curved fork will have more vertical compliance than the straight-blade fork. The straight blade fork will have a larger stress riser at the crown.

    think about a spring. It is made of gradually curving steel, not a series of straight sections with 'corners'

  13. #13
    cyclopath vik's Avatar
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    Quote Originally Posted by Bacciagalupe View Post
    Not really, because vertical compliance can also be affected by tube stiffness, tube thickness, tube shapes, crown design, angles of impact, choice of material and numerous non-fork-related factors (e.g. tire pressure and width).

    Maybe in the early days it was more difficult to make a compliant fork without curving it, but I doubt that is still the case, especially with CF forks.
    Excluding carbon which doesn't seem to be accepted as a touring fork by many can you give us a few examples of straight legged rigid metal forks suitable for touring that have design elements to deal with absorbing road vibration? All the straight legged touring forks I've seen in action seem to be uber stiff straight gauge tubing designed with disc brakes in mind.
    safe riding - Vik
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    Quote Originally Posted by Bacciagalupe View Post
    Not really, because vertical compliance can also be affected by tube stiffness, tube thickness, tube shapes, crown design, angles of impact, choice of material and numerous non-fork-related factors (e.g. tire pressure and width).

    Maybe in the early days it was more difficult to make a compliant fork without curving it, but I doubt that is still the case, especially with CF forks.
    The important modifier he gave was "tend to" . On the other hand I remember when the first straight blade mtn forks showed up on custom bikes with cantilever brakes and some of them were surprisingly compliant compared to heavy production unicrown forks.

  15. #15
    40 yrs bike touring
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    One factor not mentioned is whether the fork tubes are tapered or the same diameter over the whole length. I toured on and off pavement for two decades on traditional curved and tapered forks. Twenty years ago I settled on untapered straight 1 inch tube Type II forks buit by Steve Potts for my touring bike and tandem mountain bike. http://www.stevepottsbicycles.com/type2.php

    They have greatly improved the handling and compliance and comfort even on the Divide Ride. There are many factors influencing fork performance and I wanted to add the straight versus tapered element to the discussion.

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    Professional Fuss-Budget Bacciagalupe's Avatar
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    Quote Originally Posted by positron View Post
    The curved fork will have more vertical compliance than the straight-blade fork. The straight blade fork will have a larger stress riser at the crown.
    Yeah, I'm not sure I buy it. At a minimum, the angle of the straight fork would be much steeper than the curved, which would alter the angle of impact, which may or may not have an effect. I'd accept empirical (not subjective) evidence but have not seen any research on the topic.

    But even if we accept that the curve adds some shock absorption, you still can't look at two bikes and decide that one will be more comfortable exclusively because one has a curved fork, and the other doesn't.

    For a full touring bike, most forks are steel and curved, so it's not an issue. But since the OP is looking at light touring bikes, he's probably looking at stuff like a Specialized Roubaix, which will have a fairly straight CF fork.

    As to forks with disc brakes, it's quite plausible that regardless of curvature you need to have a stiffer fork anyway to handle the torsional forces. That said, I have never heard anyone say that "disc brakes are more uncomfortable because you need a straight / stiffer fork...."

    So other than aesthetic reasons, I don't think "curve vs straight" is a particularly relevant criteria for selecting a bike.

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    "Not really, because vertical compliance can also be affected by tube stiffness, tube thickness, tube shapes, crown design, angles of impact, choice of material and numerous non-fork-related factors (e.g. tire pressure and width).

    Maybe in the early days it was more difficult to make a compliant fork without curving it, but I doubt that is still the case, especially with CF forks."

    +1. The reality is when I order a set of fork blades they come straight. If I make a curved fork out of it, or a straight one, then I will have the same blade in a different crown. So there probably are straight forks out there with a harder edge to them, but one can adjust for that, and it remains to be seen whether a double blind test would prove anything one way or another.

    I owned a perfectly pleasing Urbanite touring bike, that at the time had straight blades on it, they now offer curved. It rode great, had tapered fork blade, didn't come with discs, etc...

    Pictures of your loaded rigs?

    Nova (and everyone else in the frame biz) sells the straight blade crowns, so you can have that lugged look. tapered blade, not suitable for disc fork, any time you want it. And there are plenty of cheap forks out there as per the Urbanite also.

    Main thing is the look, for some reason racing has sorta moved over to the straighter forks, so has BMX, and with suspension forks, so have MTBs. A straight fork mostly looks ugly to me on a touring bike, but technically nothing wrong with them.

    One small issue is that it is harder to adjust for trail, you can bend the blades, but that would really look gross, whereas with curved blades, you can curve them more or less to suit all sorts of load and steering applications.
    Last edited by NoReg; 09-22-09 at 03:45 PM.

  18. #18
    Senior Member zeppinger's Avatar
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    I think its coming down to a style thing for me. I guess that I was surprised how these more expensive "competitors" dont look as good as the lowly Surly! Is there another slightly more classic looking steel road bike (credit card touring and commuting) that I should be considering? I like the Soma Smoothie but its more expensive and I already like Surly products (my LHT)!

    Surly Pacer: Sexy!
    http://www.cyclofiend.com/cc/images3/cc229-1.jpg
    The competition: Not so much...
    http://www.gunnarbikes.com/images/Sport118web.jpg
    http://commutebybike.com/commuter-bi...3028552314.jpg

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    Professional Fuss-Budget Bacciagalupe's Avatar
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    Mass Produced Steel:
    Jamis Satellite, Quest
    Specialized Allez Double Steel
    Salsa Casseroll
    Bianchi Volpe, Imola, Vigorelli, Dolomiti

    High end steel:
    Seven
    Independent Fabrication
    Waterford
    Co-Motion

  20. #20
    Senior Member Wogster's Avatar
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    Quote Originally Posted by zeppinger View Post
    What are the advantages and disadvantages of a curved vs. a straight fork? I understand the argument for lugged vs. unlugged but I think straight forks just look bad. Are they better for some reason? I am having a hard time choosinng a new credit card tourer and most all of the bikes I look at have straight forks! Surly Pacer for the win?
    Nobody else has said this, so I will, a curved fork tends to increase the fork rake, and as you increase the rake, the front wheel becomes more and more likely to self-centre, making for fewer wheel adjustments to maintain a straight tracking. This is because the weight load on the front wheel is behind the wheel, to a lesser degree you will see the same thing on items, like shopping carts that have offset wheels.

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    Quote Originally Posted by arctos View Post
    One factor not mentioned is whether the fork tubes are tapered or the same diameter over the whole length. I toured on and off pavement for two decades on traditional curved and tapered forks. Twenty years ago I settled on untapered straight 1 inch tube Type II forks buit by Steve Potts for my touring bike and tandem mountain bike. http://www.stevepottsbicycles.com/type2.php

    They have greatly improved the handling and compliance and comfort even on the Divide Ride. There are many factors influencing fork performance and I wanted to add the straight versus tapered element to the discussion.
    I think that's what I recall, when I had my shop '80-'86 Scot Nicol lived up coast at Jug Handle farm and he showed up with some recent constructions and one of them was with a very light weight straight fork with big tubes. I was surprised I could see the forks flex.

  22. #22
    Real Men Ride Ordinaries fuzz2050's Avatar
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    Quote Originally Posted by vik View Post
    Unless I need disc brakes for a specific application I'd prefer a curved fork and v-brakes for touring. I'd say I'm about in the middle of the pack when it comes to how sensitive my hands are to injury. I have had a nerve injury that lasted for 6 months on a bike with straight forks on a very rough road and I know the transmission of vibration straight up those stiff fork legs to my bars was a significant factor in my injury. I've since added Ergon grips and double layers of cork tape to those bars. I definitely don't want a repeat injury given how long it took to heal.
    Don't forget that a disk fork is also build stiffer, in order to better deal with the forces that the disk brake applies to it. This generally means a less compliant fork

  23. #23
    cyclopath vik's Avatar
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    Quote Originally Posted by fuzz2050 View Post
    Don't forget that a disk fork is also build stiffer, in order to better deal with the forces that the disk brake applies to it. This generally means a less compliant fork
    Agreed...I just can't really think of a production touring bike with a straight fork that was not simply uber stiff. I'm scratching my head to think of a straight legged touring fork that's designed to absorb road shock/vibration. Are there any or is this just a theoretical discussion?
    safe riding - Vik
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    Professional Fuss-Budget Bacciagalupe's Avatar
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    Independent Fabrication has a steel framed light tourer with a straight fork, no disc brakes. http://www.ifbikes.com/OurBikes/Road/Steel_Club_Racer_/

    And the Jamis Aurora Elite used to have a straight CF fork, before they changed it to steel.

  25. #25
    Senior Member Wogster's Avatar
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    Quote Originally Posted by vik View Post
    Agreed...I just can't really think of a production touring bike with a straight fork that was not simply uber stiff. I'm scratching my head to think of a straight legged touring fork that's designed to absorb road shock/vibration. Are there any or is this just a theoretical discussion?
    That would be true for road bikes, however most shock type MTB forks do absorb some vibration. I think the biggest reason for road vibration causing problems is tire pressure. If you have a 23mm wide tire inflated to 120PSI, and you have a lot of problems with road buzz, then try a little lower pressure on the front tire, say 95-105PSI, see if that helps. The biggest advantage to the pneumatic tire is that it effectively acts as an air shock, inflating the tire until it's as hard as a solid tire, eliminates that advantage.

    Racers need it, because they need every last drop of speed, because often the difference between the winner and 4th place is a few seconds at best. Comfort is of little concern to the racer, especially when the cost of that comfort is speed.

    If your riding 75km a day on tour then whether you finish the ride at 2:30PM or 3:30PM is often immaterial, so you don't need those super high pressures.

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