Reach and headtube length (a proxy for stack) give some idea of how long the front end of a bike will feel. With a short headtube/low stack, you end up losing effective reach with headset spacers. So if you have two bikes with the same listed reach but one has a longer headtube, that one will fit bigger.
I agree that two bikes that appear to be similar in size on paper can fit quite differently.
Nov. 13, 2020, 12:01 p.m. - DMVancouver
Reach and headtube length (a proxy for stack) give some idea of how long the front end of a bike will feel. With a short headtube/low stack, you end up losing effective reach with headset spacers. So if you have two bikes with the same listed reach but one has a longer headtube, that one will fit bigger. I agree that two bikes that appear to be similar in size on paper can fit quite differently.