Exactly how big is soft baggage?

packerI said this already: soft bags may be ancient, pack animal-era technology but they seem to be catching on in advworld, with new products out from Giant Loop (review here) and Wolfman Rocky Mountains (below right). Some are little different to things I was throwing over my bike 30 years ago; one or two feature significant innovations.

rmsOn advrider (as well as in my own review, link above) questions were asked about the volume claims of the GL Siskiyou pannier: 34L said GL, while me and another guy measured l x h x w as near as we could and  came up with 24L.

‘Aha!’ the bloke from GL replied – we establish volume by filling out our bags with beans until they bulge out and that way get 35 litres so that’s what we rate them at. It sounded plausible and got me thinking: what is the maximum volume of a shaped, non-elastic but flexible rectilinear container like a motorcycle side pannier? Logic suggests as the box form flexes out sideways under the weight on contents, the shorter side will pull in and the volume will remain constant.

lomoEnvelopeBut intuition (or maybe logic too) suggests capacity ought to increase: the classic Envelope Test performed by an obscure, pre-Cartesian monk, Antoine de Connerie in front of a disbelieving king in 1444. An envelope is a flat container with a volume of next to nothing; open it a little and volume increases, open it a lot and volume increases again up to a point when opening it out too much will reduce volume to near zero again as it folds back in on itself.

Al Jesse and I discussed this: he reckoned volume of a rectilinear vessel is fixed, but I was not convinced and now think I have the answer: If the flexible container is a cube (l x h x w all the same) volume when filled (with beans, water, anything non compacting) will not be altered much – some fabric bulge maybe.

magdimsBut a rectilinear flexible box (‘suitcase’) seeks to attain the geometric nirvana of cubic equilibrium and does deform and expand substantially. L x w x h on my Magadans rolled up and clipped came in at 24L (left). Doesn’t sound so much and would be identical to a 24L metal box.

magwaterBut, fill the Mags with water and you’ll easily get 40 litres in each side as the pictures right and below show. Seems hard to believe but there are no less than two fills of that 20L white bucket inside the Mag bag, rolled up, clipped down and ready to roll were it not for the fact that it would give me a hernia trying to lift 40kg (88lbs).

magwalterDoes this all really matter? Yes it does because for the start, the l x w x h method doesn’t truly represent the maximum potential  volume (MPV) of a flexible, non-cuboid container, even if the maxed-out 40L capacity demonstrated on the left is unlikely to be achieved in the real world of packing your panniers with normal travel stuff.

It matters all the more when trying to compare stated fabric pannier volumes with rigid metal or plastic boxes as a guide to buying one or the other. My comparisons in the table at the bottom uses the l x w x h method but that only compares like against like. In all cases you can get more in your bags.

monbaguetteEven then, I think the dimension ratios of a flexible container may also have something to do with it. I recall the guy from Enduristan saying something like the reason their Monsoons (right, reviewed here) are wide (closer to a cube form) is that they have/can make more volume (by presumably having less far to go to reach ‘cubic optimisation’).

But on a motorcycle I still believe slimness is a desirable attribute and is something that for example, Jesse Luggage strive to maintain in their mounting systems and boxes – Al likes to boast that some of his rack and box set ups are narrower than competitors’ racks alone.

So in summary think carefully when comparing stated rigid box volumes against fabric panniers. A rigid box’s capacity is immutable but a soft bag may be more than you think.

The Magadan was tested for water volume because it is the pannier I currently own at the time of this experiment, but this test would obviously work and give similar results with any similar product. 


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12 Responses to Exactly how big is soft baggage?

  1. Jens H says:

    Did you tested the Wofman RM till now? What is your opinion about them afterwords?

    • Chris S says:

      Hello Jens. The last time I looked at a set of their PVC bags they were tough but too small to be useful. And you it seems you can’t attach pockets on the outside of PVC.
      I also found the whole rack lashing on system unnecessarily complicated – secure and good for US-style dirt bike ‘overlanding’ – not so much for day-to-day travel.
      Or if you mean the Rocky Mountain bags, I have not seen a set but after watching https://youtu.be/pnPrpZBo2Ws I was a bit put off by the build quality. Lots of straps for secure placement but that = lots of buckle time too. And again, no exterior pockets even if they are easy to sew onto Cordura. It looks like you can add strap-on a ‘Bottle Holster’ (would take 6-8 of these to have the same capacity of Magadans). In the UK Rocky Mountain listed at £380 but they cost $440 in US (=£200). If you can buy for US price then a good deal. Cone shape sounds like a good idea but for me Magadans show that it does not have to be complicated to work, and Mags certainly look bigger than RM in that video. With pockets it all means less gear elsewhere.

  2. Brun Pascal says:

    Yes Chris
    What biggest model for a journey has two??
    I wants for journey Italy Slovenia Croatia Albania Gréce many capacity.
    You has 1 bag has to advise(recommend) to me
    Monsoon ?r Spec Magadan? or another model??
    You advises(recommends) to me what
    I have Trax 45 l, damaged after the fall “sold”(been sold”)
    Now Givi E41 + top compartment Maxia 55L
    We are 2 on the motorcycle
    XT1200Z Worldcrosser with support(medium) Givi PLR
    Thank you Chris for the advice(council)
    “Google traduction”

  3. Brun Pascal says:

    Hello Chris
    For you, which is the biggest soft bag “capacity”
    For a couple in motorcycle “, 2 nobody ”
    XT1200Z with support(medium) Givi PLR
    Thank you very much

    • Chris S says:

      Hello Pascal, do you mean what is the biggest practical volume? Well a 1200Z ought to be able to carry just about anything, but 30-35 litres is about as big as it wants to be.

  4. DLA says:

    from a math point of view, a ball shape has the optimal (best) surface / volume ratio.

    Imagine you could use the fabric of the pannier to shape it into a ball shape; with the same amount of fabric, the volume of the ball will always be larger than the rectangular shape of a pannier.

    Now, off course the soft pannier will ‘reshape’ into a more round form, but never into a perfect ball, but stiil you gain volume.

    The formulas for this can be easily found on any (teaching related) math web site.

    An often used formula is the one that defines the volume effectiveness of a shape compared to a ball, both having the same surface.

    for example, a cubic shape with sides one has a volume of 1 and a surface of 6. A ball shape with the same surface, has a volume of 1,382. Therefoe, the effective volume of the cubic shape is 72,4%

    for the Magadans (200x360x360mm, cap 25,9l), this ratio is 68,1%. Or, in other words, a ball with the same surface as the pannier, has a volume that is 1,468 larger, which would make 38l

    as you stated, the Magadan volume at min closure is about 32l (rectilinear), youa gained 8l with the water in, so your ratio is 1,25 larger. That fits in nicely between recitlinear and the theoretical max volume of a ball.

    So, it is probably safe to say that the Magadans will take up to 30 l when fully closed, if you stuff ’em with flexible stuff…. ;-)

    Hopefully this is not too much math geek stuff, just meant to point out that your findings are totally logical and explainable.

    One last thing: how much a soft pannier will ‘stretch’ in volume, depends on the dimensions of l, w and h. If you do the math for the Monsoon, you will find their ratio is 71%, 1,4
    So, in theory their volume expansion by stuffing will be a bit less than the Magadans. But that is theory, not the real world :-)

  5. Pingback: Comparison: Adv Spec Magadan; Enduristan Monsoon, Kriega Overlander, GL Siskiyou - Page 3 - Horizons Unlimited - The HUBB

  6. Doug P says:

    A cube with sides of length 1 meter has a volume of 1 m³. If you could form that into a sphere of circumference 4 meters, you’d have a volume of 1.08 m³. So about a 10% increase. In your Magadan water test you’re seeing about a 65% increase (24 to 40). So yes, making the sides bulge increases the volume, less or more depending on the original shape. But I still think that it’s a cheesy way to advertise usable volume. It’d be rare for a sensible person to ride with the sides bulged out to the max. Perhaps a realistic metric might be to add 15-20% to the volume calculated from L*W*H. From a math geek (and the guy who questioned the GL volume claims on advrider).

    • Chris S says:

      Well I do say “… the maxed-out 40L capacity … is unlikely to be achieved in the real world of packing your panniers with normal travel stuff.” I never claim it to be useable volume, just a maximum potential.

  7. I’m missing the Ortlieb panniers and Wolffmann too in your comparison.

    • Chris S says:

      In the table above I have only compared panniers I have actually owned and used (#1, 2, 4), owned by friends (3), or lent a set for review purposes (5). In other words I have owned and used most of them on motorcycle travels.
      I have owned but never got to use Ortlieb QL2 and have never seen Wolfman RMs (tho may do this weekend). I have seen a set of Wolfman Expeditions – tough vinyl construction but way too small for the type of travel I write about.

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