Considering making a seat dry bag harness.

[Allan_333]

I have finished making my top tube bag, frame bag, B17 bag (under the leather but above the rails), and rear triangle bag. I have heaps of material left over, so I was thinking instead of buying a seat bag like the Pika or Viscacha. I can use the left over material and make a dry bag harness. Currently I have a 20L dry bag, although I only need 12L of storage so I will roll down the dry bag a fair bit, and it weights 2.3kg (5lbs) when filled with my gear. It will have to be attached to a carbon seat post, with a B17 saddle, with 8in of saddle rails to wheel clearance.

I don't really know how to go about making this so any help or advice would be great, and patterns or plans would also be quite helpful. I want to try to maximise the space at the seat post end of the bag/harness, I don't want to make a really long one, as I am concerned about levering force on my carbon seat post.

Also is 2.3kg (5lbs) to much for a saddle bag?

[atlantabill]

I don't have experience making a seat bag, nor dry bag harness, but I have experience making stuff sacks, sails, sail covers, etc. so here's some suggestions.  I'm interested what others may say as I'm thinking of making a seat bag.

I suggest making a prototype of cheap, weak fabric (either thin nylon, or even an old bed sheet).  The goals being to get the shape and dimensions right and to test it to failure to see where you need reinforcement or to re position the straps.  Ideally you could disassemble a good prototype and use it for a pattern, or build it from a hand drawn pattern and reuse the pattern on better fabric.

You might even intentionally sew it with weak thread to see where the thread, or seams part first.

I'd love to borrow a 'store bought' bag to make a copy, but unethical to buy it, copy it, then return it.  And you don't want to be attracting any negative karma to the project.  But if your friend has one you could borrow, that might be ok.

It doesn't *seem* that hard.  For a dry bag harness, perhaps using safety pins to temporarily connect intersecting pieces of webbing (not pinned to the dry bag, but pinning straps to straps) to test their position.

[bakerjw]

+1 for the prototyping. I keep old sheets for just that purpose. I also use a stapler rather than sewing when doing a mock up design.

I'm about to try making my own seat bag much along the lines of a porcelain rocket. I'll machine out an aluminum block to mount to the seat post with a pair of fiberglass rods running out the back over the rear wheel. This will be for anti-sway purposes. It is just an idea in my head. We'll see if it comes to fruition or not.

[fotooutdoors]

So that you don't need to start from scratch, dig around on the forum for some posts by Jerry W? He constructed a seat sling and posted a pattern. Based on my experience with that pattern, I would suggest a second dear rail cinch strap, a bit longer sling length (to accommodate the second strap) and I have played with the idea before of fiberglass stays. Perhaps connect then to the bike via a rack mount seat post clamp. Since I have a Henry Shires tap tent (the homemade version), I would aim for one to be the correct length for a support for that.

Edit: here is the link to Jerry's bag http://www.bikepacking.net/forum/diy-make-your-own-gear-%28myog%29/full-diy-bikepacking-kit/
And I think I would use something like this http://images1.mcmaster.com/mvA/contents/gfx/large/91705a500p1-b01l.png?ver=1404833011 to seat the fiberglass poles at the bike end; they would be held by tension from a strap.

Typed on my phone. Pardon the autocorrect.

[PoopdeckMcGee]

Ay, mate (fotooutdoors). I'm right in the middle of the same project. Where did you find that rod end?

[fotooutdoors]

McMaster Carr is where that one is from. I haven't constructed anything or held the eye nut in my hand, just speculated on the construction.

I think the evolution we are seeing (constructing!) in bike bags is akin to rucksack to external frame pack to internal frame pack for backpacking.

Typed on my phone. Pardon the autocorrect.