Getting two bikes of different top tube sizes to fit the same-
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  1. #1
    Reputation: lawhoo's Avatar
    Join Date
    Feb 2004

    Getting two bikes of different top tube sizes to fit the same

    I have a bike with a 23.38 inch effective top tube that, combined with a straight seat post, 110mm stem and riser bars, fits perfectly. I have another frame - classic steel from the
    1990s that has the same head and seat tube angles (71/73) but with a 22.6 inch effective top tube. Can I get this bike to fit about the same without compromising handling or pedaling efficiency? Or is it a lost cause to try a setback post and 120mm or 130mm stem? I don't want to be too far forward handwise or too far back from the cranks legwise, but I don't mind investing some time and money in fit if there isn't anything inherently stupid or impossible about getting a 22.6 ett bike to fit the same as a 23.38 ett bike. Thanks for the thoughts.

    Edit: I should also mention that the front end height of these bikes are not the same. The 23.38 has a 100mm Fox fork, whereas the 22.6 uses a fork suspension-corrected for 63mms of travel. The smaller bike would require some spacers to get the bars about the same relative height.

  2. #2
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
    Join Date
    Nov 2007
    Don't monkey with the position of your saddle relative to the bottom bracket to try to fix fit. Just match the '90s bike to the one that fits you.

    110mm is quite a long stem. Does your current bike tend to nosedive in compressions and dips, or give you trouble getting the front end up? I'd be a bit torn if they were my bikes. Maybe try a 120mm stem on the '90s bike. IMO, it's nice to have a slightly shorter reach on a bike that rides harsher, unless it makes you cramped or arch your back.

    Each aspect of bike fit influences the other aspects, so you may end up putting your saddle in a slightly different position on one bike than the other. I just don't think that's a good starting point. A more upright position sometimes means that the saddle sits closer and sometimes that it sits further. So it takes tinkering.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  3. #3
    It's about showing up.
    Reputation: Berkeley Mike's Avatar
    Join Date
    Jan 2004

    If the tube angles are the same

    and the Effective TTs are different then how do the wheel bases compare? I expect the older bike to have a shorter wheelbase. As a thumbnail a cm back on the seat and a cm forward on the stem may make the bike "fit." Yet being spread out on a shorter wheelbase may make your handling different.

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