Originally Posted by
urbanknight
This is interesting to me. Why wouldn't you want to consider the saddle's position when determining reach? I would expect the desired reach to be a product of your torso and arm lengths, which would start where the saddle is. Of course, you wouldn't want to move the saddle to change reach, but I don't understand why its position isn't a factor in what stem length you end up choosing.
Also, I've never heard a reference stating how a frame's "reach" is officially measured, and never thought it was ever a real number since reach is a function of the frame plus cockpit parts put together. I've never seen a manufacturer publish "frame reach" in their geometry charts.
Check out trek and cervelo, both used to and i think still do quote reach as do many others but not all.
Saddle position (set back ) is determined relative to the bottom bracket to get your knees at a comfortable angle and to get your ballance correct. Stand up and assume a riding position with your arms out forward - you are ballanced and have no weight supported on your arms. You can reach further forward if you want by re ballancing, or sit up more too if you like with no weight supported by your arms. On the bike your seat position determines your ballance point. too far forward and you must support yourself on your arms so saddle position does effect stem length. opposite to what you might expect, moving the seat back often ballences you so a longer stem is more comfortable
However the reach of a frame is independant of setback, you could get the set back such that you are comfortably ballanced but the front triangle of the frame is so long you cant reach the bars at all. Notice that adding spacers under the stam results in the stem getting closer to the BB as does flipping up the stem.
FWIW I can get comfortable with anything between a 90mm and 120mm stem by altering my ballance, seat back = longer stem, it just depends how much you want to be leaning forward when you are ballanced, the more you lean forward the more your back has to do. i ended up settling for a 110 stem as that position suits the riding i do. others may be different