When it comes to seat bags, I don't like the thought of a bag back there wiggling around. I ride a tandem with my wife a lot (great training too btw) and I get a lot of wiggle from the stoker position. Anyway. I know that seat bags are light and usually don't wobble too much when properly secured but I was looking for something more stable. I came across the Thule pack and pedal and like the stability that it offered. The one thing that I didn't like was the top part seemed small and I'd heard complaints of dry bags shifting around and hitting the back of your legs and such.
So... I made the following.
The materials are a heavy waterproof ballistic nylon and some 9 ounce waterproof ripstop fabric.
In order to get the Thule rack to stay put, I glued some EPDM aroun the seat stays. and then attached the Thule rack. It mounted easily and sucked down nice and tight. It is not going anywhere.
Using my experience using epoxy and leftover materials from my boat, I laid out 2 layers of cross weave fiberglass. IT is very flexible and durable.
although the fiberglass sheet that I made is durable and flexible, I needed a bit more rigidity. Rather than buying fiberglass rope, I used some 5/8" polyester rope. I made a form with vinyl and laid the rope inside on top of the sheet. The rope really wicked up the epoxy.
Here it is after cutting it out and sanding down the edges.
A test fit on the bike.
Firmly attached to the bike now.
I used a strip of foam between the aluminum frame and the epoxy sheet as a buffer.
So at this point, I had a light platform on the Thule rack. All that was left was to make the bag. It took 2 tries but I had plenty of material laying around so it went well. What I learned in the first run really helped out.
I didn't tale pictures of each step. It would have slowed me down. Here it is mounted on the platform and on the bike. One thing to note. The yellow tabs that hold the laced paracord on the top are triple sewed to the black balistic nylon. They are also 3 layers thick so they'll last for a long time.
The bag actually wraps under the platform using a lace pattern. The paracord is then tied around the seat post up front. This pulls the platform and bag forward and should help keep the rack from slipping down.
I used 3 strips of velcro to attach the front of the bag to the seat post. This should offload some of the forces of bounces on the trail to the seat post and stop torquing of the rack. I got one piece of velcro backward! ARGH... I'll split the thread and resew it properly.
I still have to work on securing the back of the bag. It is a simple tube. I have some 1/2" nylon straps and non adjustable clips that I might use. I also don't like the bulge right near the seat. I'll likely take it is lightly to give it a more rounded look.
This thing is solid and has some capacity to it. I am PLEASED.
