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  1. #1
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    Steel fork on a Ti frame

    When I had a Lemond 853 Zurich, I found the carbon fork far too stiff for the rest of the frame. Once I jumped into a sprint, the front of the bike was as hard as a rock, while the rear end flexed and fishtailed all over the place.

    Now that I'm getting a Ti frame (a Schwinn Paramount built by Serotta), I wonder if I might have the same issue with the carbon fork that is already on the frame as I did with the Lemond. If I do, what are the possibilities for adapting a steel fork onto the Paramount?

    I know there's another member who just bought a DeRosa Ti frame who may be adapting a steel fork to his front end, so it seems like a doable solution. But is it a solution?

    Thanks all.

  2. #2
    Descender
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    Only a guess here, but I would think Serotta would mate there forks and frames properly.

  3. #3
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    Sounds like a too-flexy frame combined with a too-stiff fork. Hopefully your new frame will not be as noodly.

    I would at least try the stock CF fork. Steel forks are not automatically less stiff.

  4. #4
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    Thanks guys.

    Yes, I would believe Serotta does make their own forks. Maybe something off their steel frame (the Legend?).

    But yes, I do plan to try the stock c/f fork first. I just like to plan ahead in case something is amiss.

  5. #5
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    By the time Schwinn commissioned Serotta to build the Ti Paramount in the late nineties, the use of straight fork blades with the offset/rake introduced at the crown to blade junction was ubiquitous. This was popularized by Colnago because it was much easier (read cheaper) to make straight blades than replicate the same precise curve thousands of times in steel fork blades.

    Jan Heine, writing in Bicycle Quarterly, says the problem with straight bladed forks (regardless of material) is that they transmit road shock almost in the axis of the fork blades directly to the frame through the headset as there is very little compressibility in the blade material. Forks with curved blades OTOH, especially with the curve concentrated near the dropouts, increases the angle of the fork tip in relation to road shocks, so the fork blade flexes more and absorbs shocks better.

    That's why I like forks shaped like this:

    -Stan
    my bikes

  6. #6
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    Stan - yes, but can forks shaped like yours work on my Paramount - provided I need them?

  7. #7
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    Quote Originally Posted by dd74
    Stan - yes, but can forks shaped like yours work on my Paramount - provided I need them?
    Absolutely! As long as the rake (offset) and crown race to dropout length are the same, it'll work just fine.
    -Stan
    my bikes

  8. #8
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    Which fork is that on your bike, Stan?

  9. #9
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    It's the stock Reynolds 531 chrome plated OEM fork on the 1972 P15-9 Paramount. It has a 2" (51mm) rake and 382mm dropout to crown race length (700c wheels). It has a 1" threaded steerer tube.

    Any experienced framebuilder who fabricates his own steel forks can easily replicate the dimensions of the fork you have on your Paramount, but with curved steel blades.
    -Stan
    my bikes

  10. #10
    Number 2 on the course.
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    Quote Originally Posted by Scooper
    Jan Heine, writing in Bicycle Quarterly, says the problem with straight bladed forks (regardless of material). . .
    That "regardless of material" part disqualifies his opinion on the matter. (And that's my opinion.)

  11. #11
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    Quote Originally Posted by PeanutButterBreath
    That "regardless of material" part disqualifies his opinion on the matter. (And that's my opinion.)
    How so? The compressibility of any material likely to be used for a fork is virtually non-existent. BTW, the parenthetical 'regardless of material' was mine, not Jan Heine. Sorry I wasn't clearer.
    -Stan
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  12. #12
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    You can not make comparison between a composite fork and a metal fork based purely on outward appearance. The behavior of the composite fork can be influenced in ways that do not change the shape of the blades.

    Even a metal fork's behavior can be changed by varying the wall thickness, so his assertion is specious even comparing two steel forks. For example, you could build a beautifully curved fork with such thick tubing that it would still beat the snot out of you.

    It doesn't really make sense that straight-blade forks are a cost cutting conspiracy either. The cheapest forks you can buy are curved (and steel).

  13. #13
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    Quote Originally Posted by Scooper
    Jan Heine, writing in Bicycle Quarterly, says the problem with straight bladed forks (regardless of material) is that they transmit road shock almost in the axis of the fork blades directly to the frame through the headset as there is very little compressibility in the blade material. Forks with curved blades OTOH, especially with the curve concentrated near the dropouts, increases the angle of the fork tip in relation to road shocks, so the fork blade flexes more and absorbs shocks better.


    I think that that old notion about straight forks transmitting more shock than curved forks has, for the most part, been proven wrong. Vibration doesn't travel in a straight line. Even if it did, the vibration coming off the road to the tires, wheels, etc is coming off the road in all sorts of directions. If you were to put a device at the handlebars to measure vibration and were to compare a straight vs curved fork, I think the difference would be statistically insignificant, meaning there is no difference. IMO

  14. #14
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    Thanks, Stan. I'll look into it if the stock fork doesn't work for me. One more day and this little puppy arrives home. I bought Dura Ace pedals for it.

  15. #15
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    Quote Originally Posted by dd74
    Thanks, Stan. I'll look into it if the stock fork doesn't work for me. One more day and this little puppy arrives home. I bought Dura Ace pedals for it.
    I think you're gonna love the bike regardless of what fork you decide to put on it.

    BTW, I didn't mean to say anything controversial here. Just so there's no misunderstanding about Jan Heine's article, here it is in its entirety. I'm a big fan of both Heine and Bicycle Quarterly. I'm counting on this being Fair Use.

    While researching this a while back, I came across Damon Rinard's fork deflection test, and was surprised that the Waterford Paramount steel fork with Henry James crown and curved blades, the Eddy Merckx steel fork, and the Colnago straight blade fork (material not specified) are very close to each other in terms of lateral and forward deflection and all are quite stiff compared to the Dimension, Time, and Look carbon forks.

    From Bicycle Quarterly, vol. 6, no. 3:

    Fork Blades Optimized for Comfort and Speed

    by Jan Heine

    To provide shock absorption, fork blades should be designed to flex, yet provide strength in the areas of highest stresses. The greatest stresses on a fork occur at the fork crown. Not only do forces act on the longest lever here, but there are stress risers at the bearing seats, and the fork blades are heated during brazing. On bikes with brazed-on pivots for centerpull or cantilever brakes, brake forces are fed into the fork crown as well. A well-designed fork blade should provide strength in this highly-stressed area, and flex in the lower part of the blades to dissipate vibrations. Fortunately, most fork blades do – that is why they taper from a relatively large cross-section at the fork crown to a much smaller section at the dropouts.

    Alex Singer used special Reynolds 531 fork blades on many bikes. These blades appear to be particularly well-designed. Their cross-section at the fork crown uses the tall and narrow “Imperial Oval” rather than the rounder “Continental Oval” used by most modern bicycles (Fig. 1).



    These “Alex Singer Special” fork blades continue with a constant diameter all the way to the cantilever posts to maximize stiffness there (Fig. 2). Then they taper relatively quickly to a round cross-section measuring 13 mm in diameter. The slender cross-section continues all the way to the dropouts. This design minimizes flex at the highly stressed fork crown interface, and maximizes flex in the lower portion of the fork blades.



    Modern fork makers often talk about the lateral stiffness of their forks, which is intended to provide better cornering. Clearly the “A. Singer Special” fork blades lack lateral stiffness when compared to modern fork blades: At the crown the “Imperial Oval” is narrower than the “Continental Oval.” And the slender blades can flex in any direction. Will this make the bike track poorly in corners? The answer is no. Unlike a car’s steering components, a bicycle fork does not suffer significant side load, since the bike is steered by leaning. If a bicycle’s fork underwent significant side forces during cornering, the bike would not stay upright, and the rider would crash.

    Side loads occur only when the lean is initiated or modified, and they are very small. Even when riding out of the saddle, the fork blades flex only insignificantly. Forks that are very flexible in the fore-aft direction may exacerbate problems with brake judder, but the obvious solution is to use brakes and pads that do not judder.

    In practice, I have found that my best-handling and thus fastest-cornering are equipped with the “A. Singer Special” fork blades. Riding otherwise similar Alex Singer bikes, one with standard and one with “A. Singer Special” fork blades, I found no difference in front wheel deflection even when riding out of the saddle. However, the shock absorption was noticeably different.

    I consider the “A. Singer Special” fork blades an optimized design. They provide strength where it is needed, compliance where it is desirable, and generous tire clearance as well. Reynolds also offered a similar shape, but with a shorter constant diameter section at the top, for use with sidepull brakes. (With sidepull brakes, there is no need for the constant diameter all the way to the cantilever posts.) These were used by many British builders in the 1950s. Some Italian builders also used blades with a very small diameter for a long portion of the lower blades.

    Like many classic bikes, the 1947 Alex Singer concentrates the bend near the dropouts (Fig. 3, Fork 1). This means that road shocks act almost perpendicularly on the fork blade, making the blade easier to flex than a gradual bend or a straight-bladed fork.



    Unfortunately, the “A. Singer Special” fork blades and similar shapes today are no longer available. Most bikes today use relatively large diameter fork blades that provide comparatively little shock absorption and concentrate stresses in the area of the fork crown. The current “Continental Oval” cross-section provides less strength in this area while also limiting tire clearance. The Japanese tubing maker Kasei still offers “Imperial Oval” fork blades, but the supply of matching fork crowns is dwindling. Perhaps it is time to resurrect the “A. Singer Special” fork blades and the associated fork crowns.
    -Stan
    my bikes

  16. #16
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    I think Grant Peterson wrote on the subject of fork blade curvature in an old Rivendell Reader. I don't have it around, but I note that Grant seems to spec gradual bend forks (looking at RivBike.com). I think is take had something to do with spreading the deflection along the entire length of the blades.

  17. #17
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    Well theory aside, there is an online article hosted on the late Sheldon Brown's website written by a guy that worked at Holland Cycles. They tested several forks or different curvature, material, etc. and the results showed that there was no significant difference in curved vs straight bladed forks as it pertains to deflection and shock-transmission.

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