relation between top tube length vs. stem length
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  1. #1

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    relation between top tube length vs. stem length

    Is there some theoretical or actual guidelines as to how long a stem should be relative to the top tube. I mean, would I be better off with a 58 cm top tube and a 10 cm stem, or a 56 cm tt with a 12 cm stem?

    I'm six feet tall. For the past 5 years, I've ridden 56 and 57 cm frames with 56 and 57 top tubes (c-c). I've used 120 and 110 cm stems with these frames, respectively.

    I just picked up a Giant TCR2 in a size large, with a 58.5 cm tt, according to the manufacturer (I measured 58.0 myself). This frame is suppossedly meant for traditional frame sizes of 59 cm and up. I swapped out the 120 stem for a 105. The TCR now fits perfectly, is the most stable race bike I've ridden,and is very smooth in the turns. Unlike the Cannondale, I don't have to focus and fret when I'm between riders going around a sharp turn. I would have thought that the shorter stem would make for a less stable ride, but it didn't.

    I do understand that the angles of the seat tube and head tube change as the frame sizes change, but I've been able to ride bikes with these different size top tubes by adjusting the stem length. What's been your experience?

  2. #2
    RoadBikeReview Member
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    makes little difference...

    If all other dimensions are identical, the frame with the shorter TT would have a shorter wheelbase and slightly (about 1% per cm) more weight on the front end. The shorter TT bike would also steer a bit quicker.

    I kind of prefer shorter wheelbases and quicker steering geoemtry, over brands that use more relaxed head tube angles, which produces a longer wheelbase and (generally) more trail. The minor downside is inevitable toe overlap.

    The length of stem required for riders of identical porportions can vary considerably. If one rider prefers his knee 2cm behind the pedal spindle (like me for climbing) and another prefers his knee directly over the pedal spindle, there will be a 2cm difference in the stem required to produce the same reach on the same frame.

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