Truth: there are umpteen different seat post diameters. Truth: Japanese rental bikes have seatposts that are too short, by a good 8 inches, for even a mid-sized Dutchman's legs. Dicey idea: rather than (again) hauling a folding bike when visiting Japan (a heavy version of hauling coals to newcastle) we could simply take a longer seatpost (with or without saddle) and a handful of seatpost shim-adaptor-thingies, and hope to come up with a workable match.
Anyone know which subset of seatpost diameters are most common in Japan? Or have a good guesstimate of a "safe" (adequately narrow) seatpost diameter and appropriate range of shims to pack along?