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  1. #1
    Senior Member crank_addict's Avatar
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    For replacing vintage race forks~ How does one determine rake?

    In replacing forks its fairly easy determining for wheel size but rake is a funny one.

    Is there some guide / standards showing both US 27" and also Euro 28" (700c)?

    And for 1950's to early 1990's era steel-
    During that timeline with so many variables, style, type and application of lightweights, I would think frame builders had some guidelines.

    One could pull the original frame dimensions and maybe get something close as the maker intended.
    The other is the hassle of trial and error fit / test. Inconvenient and hope of luck.

    Any suggestions, old charts, guides??
    “If the constellations had been named in the twentieth century, I suppose we would see bicycles.” ~ Carl Sagan

  2. #2
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    How about this online calculator: Bicycle Steering Geometry

  3. #3
    Senior Member crank_addict's Avatar
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    ^Thanks Jp42, calc. is quite neat. Though really after what various generations had used.
    “If the constellations had been named in the twentieth century, I suppose we would see bicycles.” ~ Carl Sagan

  4. #4
    Decrepit Member Scooper's Avatar
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    This is a pretty simple and effective method of measuring fork rake.

    - Stan

  5. #5
    Decrepit Member Scooper's Avatar
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    I guess I should have read the OP.

    I think most designers would shoot for a trail of ~55mm to 60mm, and the rake would be whatever it takes to get that trail considering the frame's head tube angle, fork length, and wheel/tire radius.
    - Stan

  6. #6
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    Quote Originally Posted by Scooper View Post
    I guess I should have read the OP.

    I think most designers would shoot for a trail of ~55mm to 60mm, and the rake would be whatever it takes to get that trail considering the frame's head tube angle, fork length, and wheel/tire radius.
    fork blade "length" is a critical dimension to end up with what you want or expect.
    If you have a frame and no fork... it will take some work.
    unfortunately, getting accurate information on a used fork or even new replacement one is a challenge.
    I really think you need it in your hands.
    As scooper wrote though, the range of acceptable or expected trail is not a perfect or its wrong attribute.

    what will surprise most though is that within limits trail decreases with additional rake for the same head angle.
    counter intuitive. and there are other things that happen with large rake dimensions. take a bike with a large rake and swing the bars left to right 15 degrees and watch the top tube rise and fall.
    Disregarding tire size, a "27" wheel will have a 4 mm larger radius than a 700c, so there is a basic modification factor.

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