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  1. #1
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    Frame Sizing Latitude

    I hate these kinds of questions but I am going to ask anyway.

    When selecting a frame, how much latitude is there to get a frame that is larger or smaller than would be ideal and then use different length stems, seatposts, etc., to adjust the fit? For example, if the perfect top-tube length (I'm guessing that this is the crucual frame measurement these days) for me is 58cm, would a frame with a 57cm top tube and a stem that is 1cm longer than would have been used on the 58cm frame still be functionally the same? How much of this kind of tinkering with frame size using stems and seatposts can one do before it really starts to degrade a bike's functionality for a given rider? 2cm? 5cm?

    Thanks

  2. #2
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    For myself, I wouldn't mess with my ideal TT length, by more than 1 cm.
    My "perfect" size is a 58 cm TT with a -17 degree 135mm stem. I also have a 57 1/2 TT with a 140mm stem . As you see, I can't go any smaller, but I could go with a 59 cm TT and a 120mm stem. I don't think that I would want a smaller stem than that.
    If your opinion differs from mine, ..........Too bad.
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  3. #3
    WA outdoor enthusiast
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    stem shorter than 120mm

    [QUOTE= I could go with a 59 cm TT and a 120mm stem. I don't think that I would want a smaller stem than that.[/QUOTE]

    I've got 12 and 13 cm stems on my bikes. I've been told by several knowledgable people that handing is not significantly different as long as your stem length does not go below 10cm. I have no experience with a stem shorter than 12.

    Can anyone who has dropped their stem length by 2 cm or more comment on the change in handling?

  4. #4
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    I have been thinking about this question too. My LBS doesn't have a lot of large frame bikes for me to test so it's hard not to speculate on the combination of TT and stem lengths. I've read many of the articles out there and used most of the online sizing calculators and so have kinda, maybe an OK sense of what might work. I think.

    It seems to me that there is a balance point with trade-offs in either direction (fore and aft )but I have no idea what the trade-offs are.

    I too would appreciate anyone's wisdom on this subject.

  5. #5
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    more than one crucial dimension...

    TT length is certainly important, but if you're comparing frames from different manufacturers or different frame sizes from the same manufacturer, the TT lengths can only be compared directly if the frames have the same seat tube angle. If the STA is different, add 1cm per degree to the TT length of the frame with the steeper STA.

    The head tube length should also be considered. I always know BEFORE I buy a frame, exactly what combination of steering tube spacers and stem angle will produce the handlebar height that I need. Some folks only look at the TT length and end up needing 4cm of spacer and a high rise stem, becasue the HT is too short. Big mistake, IMO.

    Frames that come in 2cm size increments often vary by only 1cm or less in the TT length, so the vertical differences (head tube and seat tube) are far greater than the TT difference. The only folks who are usually concerned about a 1cm difference in TT length are those who at the extreme limits of stem length (either short or long).

    To answer your question more directly, the size range should come down to 2cm. Most frames are offered in this size increment (sometimes 1cm) and only a few "compact" geometry frames span a larger range.

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