Originally Posted by
Colnago Mixte
A 5 CM stem? Sounds like you need a frame with a shorter top tube. Sliding the seat forward to decrease reach can cause problems.
Frame sounds like it's at least two sizes too big.
So to clarify, the significant back issues were when I had the seat shoved all the way back. Today I completed a 50 mile ride with the seat forward (at about the midpoint of where it would be on a non-setback post) and had only mild discomfort. I estimate that at current bar height I need to lose just 1 or 2 cm to be fully comfortable.