Originally Posted by
tFUnK
Depends on how you define "reach". The standard definition of "reach" in the context of frame geometry is defined as the horizontal distance from the BB to the top of the head tube, so it's not dependent on your bar height. If you define reach as purely the horizontal distance between some point of reference on the frame/seatpost to some point of reference on the top of the handlebar then you are correct. If you are defining reach as the actual distance between some reference on the frame/seat (eg, the front of the saddle) to the top of the shifter hoods, then this distance will also be changed when going from a 15mm riser bar to a 0mm riser bar, but not equal to reducing 15mm of steerer spacers while keeping the same handlebar, for the reason you described. You can calculate this if you know the saddle-bar drop distance.
Very insightful! Indeed I was referring to "raech" loosely as the horizontal distance between a certain point of the hoods and the front tip of the saddle, which is different than the reach used in frame geometry. And you're right, if we talk about the the distance between the front tip of the saddle and the TOP of the hoods, then yes, that distance will change because of the lower position of the hoods. Given the geometric reach of my bike, I figure the difference will be around 0.25 mm, which is insignificant.