Originally Posted by Kontact

Okay, that's a different concept. Once you have adopted and adapted to a particular set back, you may or may not be sensitive to small changes.

I had a commuter bike that I built with a Cinelli 90mm stem, despite it being 10mm too short. So I pushed the saddle back 10cm. That worked fine, so I would not agree with the general statement - lots of riders have race bikes with standard set back and French Fit bikes for touring.

However, if you took one of my race bikes and moved the saddle 10mm forward - that would be a problem and I would be too far forward. 3mm? Probably not, but maybe. For all I know, my bikes already have that kind of variation, if I wasn't careful enough with the plumb line.

A real fitting luminary I worked for - Colin O'Brien - used the term "super adapters" for folks that are much less sensitive to changes in their fit. And then there were the opposite folks that even the smallest changes caused all sorts of problems. Maybe those are the people that would be screwed up by 2.5mm. But I don't think they are the majority. And when you make any fit changes you should do so thoughtfully and expect to balance it with something else. Like raising the stem slightly.