sizing bike frames

Discussion in 'Triathlon' started by Hbw, Aug 4, 2003.

  1. Hbw

    Hbw Guest

    I'm trying to figure out what size frame is best for me. I'm 5'9", 165 lbs with a 31" inseam. Thanks
    to anyone who can at least give me a range.

    Chris
     
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  2. In article <[email protected]>, [email protected] says...
    > I'm trying to figure out what size frame is best for me. I'm 5'9", 165 lbs with a 31" inseam.
    > Thanks to anyone who can at least give me a range.
    >
    > Chris
    >
    >
    >
    5'9" with a 31" inseam makes you very long in the torso (I'm in the same boat, no email pun
    intended: 5'9" 32" inseam). Bikes that fit me best have been more relaxed geometry bikes, ones
    with shallower seat angles. This doesn't make for a good time trial position, however, since your
    hips are rolled under you. It takes some tinkering. I would say 55cm is a starting point (center
    to center).

    Fit is everything.
     
  3. Mark Hickey

    Mark Hickey Guest

    "HBW" <[email protected]> wrote:

    >I'm trying to figure out what size frame is best for me. I'm 5'9", 165 lbs with a 31" inseam.
    >Thanks to anyone who can at least give me a range.

    Frame "size" means so many different things to so many different builders that it can become almost
    meaningless.

    To some (like me), it's the distance from the bottom bracket to an imaginary line drawn from the top
    of the top tube through the center of the seat tube. That tells you how high the top of the top tube
    is, which is what you really need to know. This method is referred to as "center to top".

    Others measure "center to center", which tells you where the center of the top tube is. That's a
    nice thing to know if you're designing the frame or mitering the tubes, but the rider really
    shouldn't care where the center of the tube is (except to compare to another frame that's measured
    that way). You can usually add ~1.5cm to this number to get an approximate center to top equivalent.

    Other (QR used to do this - I haven't checked whether they still do) measure to the top of the seat
    tube. This is one I've never figured out, except that it's handy for helping you estimate how much
    seat post will be showing. However in terms of comparison to other bikes, it's a worthless way of
    measuring a bike frame (IMHO of course).

    The most important thing with bike fit is getting the "cockpit length" right. Once you've determined
    that, you can look for frames that will accomodate your necessary top tube plus stem length, and
    determine which (if any) you can comfortably stand over.

    Keep in mind that the steeper the seat tube angle, the taller the frame for a "given size". That is
    to say, a 54cm c-t tri bike with a 78 degree seat tube is considerably taller than a 54cm c-t road
    bike with a 73 degree seat tube - at least if you assume they have the same bottom bracket height...
    but that's a topic for another thread.

    Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
     
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