Review: Shimano Unzen 10 Hydration Pack

It’s not every day that a writer can legitimately say that a company has completely re-thought or revolutionized a certain type of product. Well, they say it all the time… but how often is it really true? In regards to the Unzen 10 hydration pack from Shimano, I can claim with complete honesty that Shimano …

It’s not every day that a writer can legitimately say that a company has completely re-thought or revolutionized a certain type of product. Well, they say it all the time… but how often is it really true?

In regards to the Unzen 10 hydration pack from Shimano, I can claim with complete honesty that Shimano has started from scratch and completely rethought the mountain biking hydration pack.

Specs and Features

The “10” in the name “Unzen 10” stands for the 10-liter size of the pack. The Unzen is also available in 6-liter and 15-liter versions.

The most notable and radical design feature is the X-shaped harness system. This harness is designed for maximum adjustability, thanks to an internally adjustable harness (similar to some backpacking packs), adjustments at the sternum clip, and adjustments on the straps themselves. Shimano claims this X conforms to the rider’s natural body position better than a traditional design, while also simplifying the process of putting on the pack. Instead of having to clip and adjust the waist belt, sternum strap, and shoulder straps, there’s just one clip and two main straps. Shimano also claims this system increases stability as well as airflow around the sides and through the arm pits.

Side zippers

Keeping with the ergonomic theme, the pack itself is curved to match the curve of the rider’s back when seated on the bike. The outside of the pack also mimics that curve, helping to reduce bulkiness. More on back curve below.

One of the coolest features, in my opinion, is the stretchable fabric used. This stretchy plastic material is sleek, shedding mud and water, and allowing air to flow easily over the pack (not that aerodynamics are a big issue on the mountain bike). Also, this stretchy fabric allows the pack to expand naturally if you continue to stuff gear into it.

The side zippers provide access to gear inside the pack. There’s one side zipper for the dedicated hydration reservoir compartment and zippers on both sides allowing access to the main compartment. These side zippers make the curved profile of the pack possible, but also make for very easy gear retrieval.

Excellent zippers

One small item that I really loved: the zipper loops are super easy to grab and use with your finger tip in a hurry. No more messing with small, slippery, metal zippers!

There are plenty of other bells and whistles, too:

  • Breathable back panel
  • Fleece-lined electronics pocket
  • Pump holder, tube holder, and tool holder in the main compartment
  • Stretchable side pockets
  • Key clip
  • External armor storage (not available on the 6-liter model)
  • Light loop for a taillight
  • Water hose clip

Finally, the stock water reservoir is a tried-and-true Hydrapak hydration system. For more on Hydrapak’s reservoirs, check out this article.

Out on the Trail

At the beginning of this article I said Shimano completely re-imagined the hydration pack… and that’s true. However, when the tires hit the dirt this revolutionary pack only offers mediocre performance.

Don’t get me wrong, the construction is superb. If you can’t tell from my glowing rehearsal of all the unique features crammed into this sleek package, I love the construction and the attention to detail. I also love the form-fitting concept in principal… but it has two fatal flaws.

Flaw #1

According to Shimano, this pack is supposed to conform to the curve of your back when riding. When I first heard this at Interbike, I thought that sounded like a smart idea. However, after getting coached on my body position and pedaling with Eddie O’dea, professional bike fitter and ultra-endurance-mountain-bike-freak-of-nature, I learned that when climbing, you should try to keep your back straight. This reduces stress in your lower back and also allows you to engage your glutes effectively, providing maximum power to make it up the mountain. What happens when you try to straighten your back while wearing a backpack that is meant to curve? Nothing good.

Of course, when you get out of the saddle, especially while descending, that curve naturally returns to your back. But in my experience, long grinder climbs make small things, such as an awkward hydration pack, feel the most annoying… not so much on the exciting descents.

Fatal Flaw #2

It turns out the Unzen has yet another fatal flaw that proves irritating on the descents as well. This, again, has to do with the fit, but primarily with the X-harness.

Shimano claims the X-harness is supposed to make the pack more secure on your back than a traditional design, but I found when it’s fully loaded with water and tools, this pack is actually less secure than most traditional designs. It rides fine and doesn’t jump much up/down, but I’ve found the Unzen has an annoying tendency to swing to one side or the other in rough descents, and especially in fast turns. The pack tended to swing to the outside of the turn, and then get stuck riding on that side of my body until I manually adjusted it. And then it would be fine… until it would swing again.

You might ask, “are you sure it wasn’t too loose? Couldn’t you tighten the straps down more?”

I found if I cinched the straps down tight, it did minimize the side-to-side sway–but didn’t eliminate it entirely. However, cinching the straps that tightly caused yet another issue. Bearing in mind the pack is designed to fasten directly over the sternum, cinching the straps too tight inhibits your breathing. With the pack cinched tightly over my sternum, my chest wasn’t free to expand to allow me to suck wind on those heinously steep singletrack climbs.

I then had to choose: loosen the straps for free breathing, or tighten straps and reduce pack sway. The loosened straps won out.


I sincerely applaud Shimano’s willingness to innovate and throw out convention, designing the Unzen from scratch. However, it seems that some features are standards for a good reason. The construction and details on the Unzen 10 are excellent, but in application there are a few major flaws that prevent me from truly endorsing it. If Shimano could fix these issues, I would be all over this pack!

On the other hand, if your body shape has not meshed well with any hydration pack that you’ve tried previously and the unique fit system on the Unzen sounds appealing to you, it might be worth your time to give the Unzen a look. Who knows: maybe my body shape just doesn’t work well with this design. Jim seemed to enjoy the Unzen so check out his article for an opposing view point, click here. But if you have the opportunity, I would at least encourage you to try before you buy.

MSRP: $100.

Many thanks to Shimano for sending over the Unzen 10 for review.