Originally Posted by
dalava
Well, you know the top tube length, and seat tube length, and the interior angle where these two tubes meet, and let's call that A. And let's call the end point of the top tube B, and end point of the seat tube C. It's simple trig to find the dimensions of the triangle. The head tube length actually doesn't matter here. From there, it's just a matter of finding the height of the triangle from point C to line AB, and, and the length from where the height line bisects line-AB to point B for reach.
This should be pretty simply, am I missing something here?
Sorry, you are being overly simplistic. It is more involved than that. Not hard by any stretch...but you don't know the interior angle you mention...it isn't the complement of the sta...as most bikes today don't have a horizontal top tube...have effective and actual top tube length. You need all the dimensions the OP mentioned plus BB drop.
OP...you can get a simple free 2D CAD software on line as well. Pretty easy to plot everything. Also if somebody posts the equations, I will check them with my Roubaix. I know all the dimensions on the bike including stack and reach.