Because Trek designates frame size based on variables that include no methodology.
I’m currently swamped with prospective customers and frustrated sales-people, trying to determine:
1. Saddle Height
2. Arm Pad Stack
3 Arm Pad Reach
4. Base Bar Stack
5. Base Bar Reach
It is easy to find these dimensions on the Serotta Fit Bike, but most bike-shop staff are without the means and/or time to do the same.
Hopefully this will help:
The Speed Concept CAD generates approximate saddle, arm-pad, and base-bar coordinates to place orders with Trek. It will also provide an exacting model, which can be manipulated for personal preference.
Thanks, Brent. You are the master of Bike CAD.