Originally Posted by
Sy Reene
Ok, but you have HT and ST angles and fork rake. HT and ST angles are dependent on bike being horizontal. If you adjust the horizontal line, then the HT and ST angles would change and move away from the published values, right?
[QUOTE=RChung;20819034]HT and ST angle give you a horizontal line, but there are infinitely many horizontal lines. The one that matters is given by BB drop, which not all geometry tables give you.[/quote ]
I sort of disagree. All horizontal lines are parallel. Once one has a horizontal line, one can lay out seat- and head-tube angles. Stack is measured from the center of the BB shell to a horizontal line extended back from the top center of the head tube. Fork length has nothing to do with it.
The bike’s head- and seat-tube angles were calculated of the horizontal---and all horizontal lines are parallel. The lines between the axles, the line through the BB shell center, and the line extending back from the top-center of the head tube—there is only one “horizontal.”
BB drop is just how far the BB is blow the horizontal connecting the two axles---but since it is horizontal …..