All of my bikes use 27.2 post size. 3 are made for that size and the couple mtb that are 30.4 I use a shim. Ever one is set back. I have never bent a seat post and am 250 pounds. I ride rough roads,single track, cow pastures and fire roads. I am not gentle on my bikes. I have a thompson elite on my touring bike and bought it only for the name. I also have Zipp and Velo Orange gran cru. Those are the only ones that i have that are name brand, the rest are unbranded as cheap as I can find. The velo is not a two bolt design. It does use 2 bolts but not to adjust the plane of the seat. Imo the Thompson is the best seat post there is, certainly the best I own.