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Frame Geometry Question

  • 17-01-2010 6:32pm
    Registered Users Posts: 1,831 ✭✭✭

    My new frame has the same length top tube as my previous bike but longer down tube, seat tube and head tube. i have tried to figure out how these changes will affect my riding position to no avail. any advice would be greatly appreciated


  • Registered Users Posts: 208 ✭✭sean_d

    Probably, you'll be sitting a little higher off the ground (your hands will almost definitely be higher anyway) or need less seatpost showing to get the saddle at the right height.

  • Registered Users Posts: 739 ✭✭✭papac

    I would say you would only be sitting higher from ground if bottom bracket height is further from ground.
    Longer head tube means higher minimum bar height. Depending on how many spacers under your bars on old bike you may be able to get similar bar height.If you do end up with higher bars you may need a slightly shorter stem to compensate imo.

    Seat tube length doesn't really make a difference-you compensate with seat post up/down.

    Seat tube angle does make a difference to position however.For one degree of difference in seat angle you have to move your saddle fore/aft by about 10to 25mm (dependin on seat post exension /type of frame) to achieve same pedalling position.Again you may need to compensate with stem as saddle to bar distance will change.(If you put bikes beside each other with bottom brackets aligned you can see difference in seat angle)

    If you are happy with your old position you can duplicate exactly using this.

    Vids on basic frame design.

    Why top tube length is not the whole story and seat angle has to be considered.
    first presentation.