Seat Bag Sway?

[Jasper_GB]

Probalby a stupid question - but i am a newbie so lighten  up a bit, eh?

Anyway, I am trying to figure out how to strap a dry bag to my saddle rails/seatpost and so far haven't been able to get it overly secure.  My method so far has been to wrap the rolltop down tight - wrap it around the seatpost 1.5 times (if that makes any sense?) and then have one strap going to through the saddle rails and around the bag (to suck it up) and one going from the seatpost and around to the back of the bag (to suck it forward). 

Any tips on this?  What am i doing wrong?  Will there always be a bit of sway with this method?  I got it fairly stable - but i think that it would become a real pain in bumpy singletrack type scenarios.

Thanks!

[Marshal]

Plug for seat specific bags--

It is pretty easy to get a dry bag to work on the front bars.  The main issue there is rubbing a hole through the bag which is easy to solve.

However when you put a dry bag on the saddle rails/seatpost, in addition to rubbing a hole in the bag there are a couple of other common issues to over come.  Irritating inner thigh rub, shifting straps, complicated pack/unpack, sometimes major interference with shifting your weight behind the saddle and as you have pointed out bag sway on single track.

I have been down this path and all I can say is with enough DIY test and trial you can overcome to some degree most, but not all,  of these issues.  

Or you can make or buy a seat specific bag.  They sway a bit also and depending on specific ‘load’ it can be quite noticeable.  For me I soon get use to my particular ‘load’ (including pack, seat, frame, tank and handlebar bags) and how it affects handing in technical terrain.  This is one reason I train with some or all of my various bags.

Anyway, once you get spoiled by the benefits of a well designed seat bag vs a strapped on dry bag, especially that easy-quick pack/unpack convenience, its hard to see why anyone would use the strapped on dry bag method.

[tonymason]

Jasper,
I have found strapping the fold-up end of a dry bag to the frame then the main body of the bag to the seat works well. It is very stable and keeps the weight lower and centered compared to strapping it to the seat and post. I leave a seat wedge bag on to maintain the right angle and provide storage for frequently used items. Though not as cool as a designed seat bag it is much cheaper, lighter and waterproof. Plus the dry bag doubles as a camp pillow, bear bag for your food, etc.
Tony

[Mike Brown]

Nice old school syncros post.