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Truth in Advertising: Dry bags vs panniers

Old 04-26-16, 04:29 PM
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northerntier
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Truth in Advertising: Dry bags vs panniers

I have the ortlieb sportpacker plus's. One pair: 30 L

I just picked up a Sea-to-Summit eVAC dry bag: 35L.

And yet, I can fit more in a single pannier than in the dry bag. I understand they must be quoting volume before rolling the top, but still, this is pretty horrendous. Despite claiming a volume of 17% more, the bag at most seems to have only half the volume of the ortlieb pair.
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Old 04-26-16, 04:48 PM
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indyfabz
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Sure it's the size you wanted? Where did you pick it up?
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Old 04-26-16, 05:33 PM
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I just looked at both the Ortlieb and Sea to Summits web sites and their spec/dimensions appear to supoort their claimed volumes. So is you STS bag 28-13-8 in size? I have some STS bags (compression) and they measure as list by the manuf.
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Old 04-26-16, 05:51 PM
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Yeah. I am wondering whether the OP bought the wrong size or was sold something by a seller that was not as advertised. (The eVAC comes in several sizes.) That's why I asked where he purchased it. I find it hard to believe that a company with the reputation of STS would grossly overstate the capacity of a product.
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Old 04-26-16, 06:15 PM
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I just went through buying panniers, an comparing them to backpacks and such I already have, I can't find a general consensus on who is right and who is wrong (or how one measures such things), but I can guarantee you that the 30L Nashbar panniers I went with are not 60% of the size of my 50L Kelty backpack I was using as a benchmark.
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Old 04-26-16, 06:24 PM
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Fill it with water and weigh it.
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Old 04-26-16, 10:04 PM
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To expand:

Weigh both dry and full, then subtract the dry weight from the full weight.
The rest is water, which is 1kg/L.

You can hold it on a bathroom scale and of course, subtract your own weight as well.
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Old 04-26-16, 10:42 PM
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It is to some extent interesting... But the fact is you determine what you want to take; you decide on bags that will carry that load; you find racks that are a proper fit for those bags, then you get a bike that carries the gear you need to take through a combo of BOs and rack mountings.

Normal process is to buy a bike one likes; struggle to find racks that fit; hope to find bags that fit the racks; start packing.

Either way I have never really cared how many liters they were supposed to hold. That is an abstraction that even if reliably calculated is not how it works.

Last edited by MassiveD; 04-26-16 at 11:06 PM.
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Old 04-26-16, 11:00 PM
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Originally Posted by northerntier View Post
...they must be quoting volume before rolling the top.....
depends how you define rolling. does folding over one time count
if it seals the bags? how many times are you folding over before
you calculate the volume? one time? two times? until bag top
is even with top of rack? as many times as possible?......
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Old 04-27-16, 08:58 AM
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I would be hesitant to fill a 30 liter dry bag with water and try to weigh it. That might be so heavy that it would break the dry bag.

If the dry bag is cylindrical, what is the length and diameter? It is pretty easy to calculate the volume of a cylinder to get a close approximation. If you do not remember your high school algebra, that is what Google is for.

The weight of one half of 35 liters of water in one pannier would probably not do damage since Ortliebs are pretty robust. If you want to keep the pannier dry, put a garbage bag in it first before you get out the garden hose. But a garbage bag might leak, so be prepared for a wet pannier.

I have a 31 liter Ortlieb dry bag and it by far is bigger than one of my Ortlieb back loaders that are rated for 40 liters for the pair.

Last edited by Tourist in MSN; 04-27-16 at 09:10 AM.
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Old 04-27-16, 09:19 AM
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I think the "standard" rolling of a dry bag is.... 1 and 2 and 3 and Snap!
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Old 04-27-16, 02:47 PM
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It's the STS evac Drysack, oval base, ostensibly 13x8x28 inches. If rectangular, this would equate to 47 liters. It's oval, so 35 sounds reasonable.

However.....

1) Measuring from *top* of the roll top (not rolled) to where the base begins, it's 26".
2) It might be 28" if the base extends down 2". However, if full, the base pulls taut and flat. So this is 26" at best.
3) STS specifies rolling the top down a minimum of 3 times to make it watertight. When I do this, assuming a flat base, I get 17" of useable height, at best.

Here I'm defining "rolling" as one turn, 180 degrees. Not sure if this is what they mean. If they mean one roll is 360 degrees, you are closer to 15" tall.

So the dimensions are bogus. It's possible it might hold 35L if you use it complete open.

Bottom line is that this is really about the size of one big pannier. This is what I had expected (friend has one), I just wanted to warn folk (and let off a bit of steam).

Last edited by northerntier; 04-27-16 at 02:51 PM.
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Old 04-27-16, 03:20 PM
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Originally Posted by northerntier View Post
It's the STS evac Drysack, oval base, ostensibly 13x8x28 inches.....
Did you measure that width and length or were you reading the specifications?
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Old 04-28-16, 12:20 PM
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I use the identical Evac Drybag on top of my rear rack. Excellent product. From kayak and canoe touring experience I use the roll down method mentioned above: " 1 and 2 and 3 and Snap!"

Usable volume depends on your number of roll down folds. Companies do not know what your method will be but seem to err in their favor when specifying volume. I have a 50L drybag for when I misjudge the volume of equipment I intended to fit in a 35L one.
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