Originally Posted by
csport
I wrote that the fit is determined by the relative position of the butt, bottom bracket and hands.
Yep, I pretty much said the same thing. So is this an argument about who said it first? <grin>
The position of the saddle w.r.t. the bottom bracket can be adjusted by moving the seatpost in/out and moving the saddle forward/backward.
Well on a road bike geometry, the proper saddle height only has a range of about 1 inch. So that amount of travel of the seat post in and out isn't going to change the butts position with respect to the riders reach to the bars much. Nor is moving the saddle fore and aft, which isn't really for adjusting reach to the bars. And if you have to buy a seat post with lager set back then that can get expensive if your bike has anything but a round seat post.
What is left is the position of the hands w.r.t. the bottom bracket, and that cat be modeled using frame stack and frame reach.
Sure but not if the bike manufacturer doesn't give you the information about the size stem as well as the bars so you can figure their reach and drop into the modeling. Drop bars have way different reach and drop to them. Currently I'm liking the short reach shallow drop bars on my new bike more than the more conventional drop and reach of my much older bike.
And your stem and handle bar height will also depend on how long that steerer tube is sticking up out of the head tube. I've never seen that given in bike specs or geometry. Though most new bikes seem to come with about 30 mm of spacers under the stem.
Still, I think I'm missing what ever it is you are trying to convey. Maybe some future time in another thread all will become clear! <grin>