Originally Posted by
Racing Dan
Mistake maybe? The top tube length, that I would argue is as important, if not more, does in fact change as expected. Smaller bikes do tend to have different geometry than their bigger brethren. Usually steeper seat tubes, slacker head tubes and more trail (unless a fork with more rake is used on the smaller model). I agree that many smaller bikes get screwed in the geometry department. I believe its mostly because of fear of foot-front wheel strike and because many manufactures spec the same fork rake for all the models even if they have slack head angles. Imo, Outside of reach this particular bike does not look too bad. Many small bikes have much slacker head angels and much more trail. Trek tend to spec different forks for the smaller models.
It isn't a mistake. As several people have pointed out, a horizontal measure that intersects a 73° head tube is going to vary as the head tube gets larger or smaller. Reach is just a poor tool for comparing frame sizes unless stack is already very close.
So the "same" reach on two bikes with different stacks are actually different reaches. Add spacers to the lower stack and watch the reach get shorter.
ETT is a better tool, but you have to normalize it for differences in seat tube angle. 1° = 1cm of TT length.