Easton EC90 SL Carbon Seatpost with 20mm Setback 27.2 x 350mmEaston EC90 SL Carbon Seatpost with 20mm Setback 27. 2 x 350mm. The Easton EC90 SL ISA Seatpost combines Eastons superlight unidirectional carbon with their patent pending saddle adjustment functionality allowing for perfect fitment. Eastons ISA technology allows you to refine your positioning without needing to undo your rail clamps for each minute tweak Saddle angle is then locked in place so you have the confidence your saddle will stay put after