Here's my problem. I have a topeak beam rack and bag that floats behind the seat. I've been looking at a new bike and that's the problem. The current has a round alum seatpost that the topeak clamps around. The planned bike seatpost is oblong like the cross-section of an aircraft wing. Since I use the bike for commuting I use about 1200cc of storage, mostly for clothes and do not want to use a back pack. Back pack would be just a temporary solution, but not acceptable for the long run.
No one seems to make any way of attaching the bag to the bike. Oh, I'm looking for a solution that does NOT involve a rear wheel mounted rack. So I can only think of two potential solutions.
Solution A - modify a seat post clamp
Basically use radiator type of clamps to hold the clamp tight and attach beam rack to it.
It would be pretty ugly, so would have to use electrical tape to smooth out the lines.
Solution B - mount to the saddle
Here would have to make a Y shaped gismo to connect to the sides of the saddle and then have a single bar/tube coming out back. The weight of the bag could be held by the bag straps, and this Y connector would just keep the bag from swinging wildly on turns.
If you have a Solution C, I would love to hear it. Oh, except ride two bikes. That solution is not acceptable to finance.