DIY seatpost-bag - waterproof, lightweight, trail-worthy

[kaivi]

Hi everyone,
after a first multi-day ride (much of it on single trails) with a single-wheel Trailer, I decided to go for something less BIG.

The idea:
A waterproof Ortlieb-style bag in a light Support (to keep the bag in shape and prevent it from wobbling around), attached with straps.
For a first prototype I found some nice aluminium-brackets on the web, a short length of waste-pipe (cut in half along ist length) from the Hardware store, and some nylon straps and small parts, that's it. two nylon straps around the circumfence, and one in Y-shape from the saddle to the lower end of the support (keeps the bottom of the bag away from the tire). The bag is from Overboard and has an additional D-ring at the side, perfect for fixing the bag while closing tightening the straps. All in all about 450g, not bad for 5l completely waterproof content. The top end of the support touches the saddlerails and will help reduce the stress on the bolts to prevent them from breaking (they don't like bending). The same goal have the washers under the screws.
The first test rides are very positive. No problem to get behind the seat for steep descents, no wobbling around, waterproof and reasonable light. Before going on a longer ride I will modify the support to go a little bit higher, that will give about 5-7cm room to lower the seatpost for rough and steep terrain.

Not the lightest bag, nor the biggest. But waterproof and compact for travelling over rough terrain.
What do you think? Any comments or ideas for improvements? Or experiences with similar setups?

Bye, Kai

[pavementgraveldirt]

I like the bag and holder combo.  Is there any leg rub? Would there be if you ran a bigger bag/holder?

[kaivi]

I like the bag and holder combo.  Is there any leg rub? Would there be if you ran a bigger bag/holder?

Hi,
no, there's enough room. The waste-pipe keeps the bag in shape, so it's a little bit longer than wide. I think, that even with a larger Diameter waste-pipe there won't be leg rub. But just try yourself, strapping a bag into this position and take a short ride down the road.
More of a problem is the room to the tire when riding a full suspension. In my setup I can lower the saddle about 5cm without touching wheel and bag in full compression. If you're riding a hardtail, there's enough room to spare.
For me, the bag holds sleeping bag, biwi and mat. That's enough, the rest will go into the front bag and a backpack.
Bye Kai

[wahday]

Well done!

[kaivi]

Thanks!
I just had my first test-ride with the front-bag, a flat Ortlieb saddlebag straddling the top-tube. I Keep you posted!
Kai

[werkinit]

Nice! What diameter pvc pipe did you use and what size dry bag please?

[kaivi]

Hi,

the bag is a 5 litre bag from overboard (http://www.over-board.co.uk/waterproof-dry-tube-bag-5ltr-yellow.html), it's a pretty tough material, stiffer and thicker than ortliebs standard material. A plus is the D-ring attached at the side which I use for keeping the bag in place while fixing it to the seatpost. The diameter is 19cm
The pipe is a standard DN110 wastewaterpipe (110mm diameter).
The smaller diameter of the pipe will force the bag into an oval shape which will prevent you from hitting it with your legs.

Bye Kai

[werkinit]

What length is the finished pipe bracket you made please?

[kaivi]

Length is 24cm...

I just started finishing the top tube bag, stay tuned ;-)

[kaivi]

and now the toptube-bag:
http://www.bikepacking.net/forum/diy-make-your-own-gear-(myog)/diy-toptube-bag-waterproof-lightweight-trail-worthy/

[kaivi]

Hi,
I made two 2-day 1-night trips with both bags, in general they are working good and I had a lot of fun (but less sleep).
But after the trips I have some improvements in mind:
Since the diameter of the bag is bigger than the diameter of the tube used for the support, I hoped ita "wings" will give the bag an oval shape to keep it from touching your legs. Unfortunately it also makes attaching the bag in the support and closing the straps complicated, especially when the bag is full. It won't fit really snug into the support.
Since there is enough room between bag and the legs, I will reduce the pipe from a half circle to a third (cutting about 2cm along the length of the tube on each "wing").
Longer test ride is scheduled for september, here some impressions from the two rides...
Kai

[kaivi]

Changes done...