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Thread: HJ dropper ST size

  1. #1
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    Default HJ dropper ST size

    I am looking at using a seat tube that Henry James sells for oversize posts and it says the seatpost diameter is 33.1mm.
    How have those who have used that tube (or another fat ST) reduced it down to a 31.6mm?
    Paragon doesn't make a step-down collar in that size and I would prefer to avoid using a shim.
    And I don't have a lathe either.
    Who has solved this riddle and how?
     

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    Default Re: HJ dropper ST size

    Quote Originally Posted by Rich Beaudoin View Post
    I am looking at using a seat tube that Henry James sells for oversize posts and it says the seatpost diameter is 33.1mm.
    How have those who have used that tube (or another fat ST) reduced it down to a 31.6mm?
    Paragon doesn't make a step-down collar in that size and I would prefer to avoid using a shim.
    And I don't have a lathe either.
    Who has solved this riddle and how?
    Nobody did their math.

    34.9 - upper bulge wall thickness x2 (3.2mm) = 31.7mm

    *** 34.9 mm (1.375") Single Butted Seat Tubes - SEAT POST DIAMETER = 33.1 mm (wrong) 1.6\.8mm = from HJ ***



    Thomson Elite 125mm 31.6mm

    - Garro
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    Default Re: HJ dropper ST size

    I was under the impression that the 33.1 was a external butted seat tube that offers a 30.9 mm I.D. for that popular size. That yields a 1.1mm wall thickness which makes sense to me. I am not basing that on any info other than the Reynolds tube that is similar in dimension.
    Drew Guldalian
    Engin Cycles
    www.engincycles.com

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    Default Re: HJ dropper ST size

    Quote Originally Posted by EnginCycles View Post
    I was under the impression that the 33.1 was a external butted seat tube that offers a 30.9 mm I.D. for that popular size. That yields a 1.1mm wall thickness which makes sense to me. I am not basing that on any info other than the Reynolds tube that is similar in dimension.
    I take it as a 4" long internal butt acting as an ex-butt essentially, here's the blueprints, it's a stock part for cromag bikes, so it comes in two lengths, here's the spec sheet:

    http://www.henryjames.com/TTpdf/VERUSSTMAG.pdf

    I'm going to say it's for a bike like this, which specs a 31.6 post:

    http://chromagbikes.com/frames/samurai#Specs

    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    Default Re: HJ dropper ST size

    Now that I think about it, it looks like someone subtracted the thinner wall number from the butted section to get that number (34.9 - 0.9 - 0.9 = 33.1) and put that on the website.
    Thanks gentlemen
     

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