I've got a feeling it's the geometry of my body. I have a standover height (true inseam) of 29". So I should be perfect on a bike of 50cm. And I am. The 50 cm frame fits fine, but to get the right pedal length I need the seat fairly high. Maybe my pelvis is deep. Who knows? And then, if I want the bars equal to the seat, the standard quill stem on an older road bike doesn't allow enough adjustment. I hope that explains it better.