Between sizes?
If your measurements put you between two frame sizes, either will usually work. The deciding factor is reach, or how long the bike feels once you are in the riding position.
Reach is driven mainly by upper body length, which we gauge using the Ape Index: your arm span divided by your height.
Positive Ape Index
Arm span longer than height, so a longer upper body. Consider the larger frame.
Negative Ape Index
Arm span shorter than height, so a shorter upper body. Consider the smaller frame.
