I thought I would share my idea for a rear bag mount on a brevet bike. I have never been fully satisfied with many of the options that I have seen and used over the years, both functionally and aesthetically. I have used racks with trunks, seat post mounted tailrider bags and dangling seat mounted bags. I eventually came up with this idea which I have not seen before. I think it is a simple, elegant and functional solution to adding carrying capacity to almost any bike. It is both economical and versatile as well as ridiculously simple!

This will allow you to mount almost any handlebar bag to the rear of your seat.  There are two ways that you can do this.  First, you can find  a stoker stem that fits your seatpost (mine is 27.2).  Second, you can use a standard stem along with a seat post shim that reduces from 28.6 to 27.2.  This fits the stem to the seatpost perfectly. The seatpost shim is way too long so you will have to cut it to the length of the stem clamp.  Next you can either cut some old handlebars down or buy some 1 inch aluminum tube from Home Depot and mount that in the stem.  All you have to do now is attach your bag mount to the rig and put on the bag. My Brooks B-17 saddle and Rock Shock suspension post are shown in these pics. A suspension post limits your height adjustment but this still works for me.

Pictured here is a Detours bag and quick release which work just fine. You could also use a Klick-Fix type mount which Berthoud uses or any number of other handlebar mount bag systems. It is super stable, lightweight and keeps the bag closer in than many rear bag systems.  A couple of tips on this. I have found that a short riser stem works best.  This one is a 75 mm/125 degree stem by Dimension (QBP house brand) and was $25 new on ebay. Stoker stems are much harder to find and are generally longer and shallower. They also cost much more!  Good luck on putting your own rig together. Feed back is welcome!