A setback seatpost of 20mm will need to clamp the rails of the saddle 20mm further to the rear of the saddle than the zero post to achieve an identical seat position. Sometimes, that is not possible because the rails don't go back that far.


Zero setback posts were created for MTBs, and are often misused on road bikes that are designed to be paired with setback posts. Make sure you have appropriate setback to your position.