For my latest project (Renovo R1) I am using a U.S.E. thermoplastic seatpost shim. It works like a charm, but it looks like crap. Like the one in the picture below, the top bit sticks out of the frame.
Would it be an issue if I would cut down the top bit of the shim, other than the risk of losing the shim in the seat tube or a tricky installation?
