Description Seatpost shims can be used to adapt smaller-diameter seatposts to larger diameter frames. One application for this shim is to put a 27.2mm seatpost on an Aventon ebike. Specs For the Aventon Pace Generation 1 traditional "step-over" ebike, a 27.2mm to 31.6mm shim is needed. For the Aventon Pace Generation 1 step-through "low-step" ebike, a 27.2mm to 30.4mm shim is needed. For the Aventon Sinch Generation 1 (step-through and traditional) ebike, a 27.2mm to 30.4mm shim is needed.