Originally Posted by
rruff
The HTA has only a tiny effect... they are all ~72.5 +-1 degree. It's the HT *length* that has a large effect... *if* you are measuring at the top of the HT.
I think you still misunderstand. If you take the Reach at a fixed height above the bottom bracket, and you have determined that a frame with 400mm Reach gives you the correct extension with a -6 110mm stem, then this will be true of every 400mm Reach frame you look at. You won't need to screw around with adjusting for HT length (or Stack), to figure you what the proper stem length would be.
What you are doing rruff is speaking into a long vacuous tunnel with no light at the end. They aren't going to understand it any more than they did the third time you and I repeated ourselves. Time to give it up bro. They don't get the importance of sta aka the horizontal relationship of saddle to vertical BB centerline. Have a look below. Below is Cervelo's feeble attempt to pacify all the simple minded guys who can't digest the importance of frame dimensions in totality...enter stack and reach. Reach is a mis-nomer as you have tried to explain. Cervelo's definition of reach is from BB vertical centerline to steerer center. That of course is ridiculous. Reach is from the saddle to steerer or handlebar center. The most grevous oversight of Cervelo's effort to placate the 'top tube club' is complete lack of factoring in the critical relationship of saddle fore/aft position relative to BB vertical center...not being part of the equation of reach relative to seat tube centerline. This generally is the starting point of any decent fitter. Stack is just a metric for keeping score of the vertical height of the head tube. I personally believe it to be more meaningless than head tube length...it is simply a method of tracking the height of the head tube taking out HTA which is a factor when looking at head tube length for net height of the bars.
