Union 34 Seatpost Mount Bag and Quick Release Seatpost Fixing System

The Union 34 Stripe Rucksack with seatpost mount option looks like a really good idea on paper: pop it on your bike for going to the station (for example), park bike, pop rucksack on your back, away you go.

The alternatives are a normal backpack and getting off your bike with a sweaty back, or lugging a pannier when you're off the bike. Combining the best of both worlds could be a winner, but the Stripe doesn't quite deliver.

The Union 34 Stripe has an inner plastic frame around the sides to help it retain its shape when mounted on the bike, a padded back and shoulder straps and a reinforced handle. It has dedicated storage compartments for a laptop (complete with 15.6in padded laptop sleeve), documents, clothes and tools. The bag is expandable to 30 litres.

The mount system has a maximum load capacity of 7kg. Bearing in mind the nearly 1.5kgs for the backpack, that limit might be a bit low for some. With the seatpost mount coming in at a hefty 795g, the combo weighs more than many rack and single pannier combinations.

The mount, to be purchased separately, consists of two parts; the rucksack attachment part can be configured in a horizontal or vertical position, allowing you to mount the backpack accordingly.

Fitting the seatpost mount to the bike is straightforward, and - according to the bumpf - fits post diameters between 27.2 and 31.6mm with the shims provided. As said shims are strips of rubber, fitting the mount to smaller seatposts could easily be bodged. It's a sort-of quick release system, in that it has a cam, but not, because an allen bolt secures the cam lever in place. Make of that what you will, but once in place it definitely won't move. Easy enough to install, anyway, and quick enough to swap between bikes. Best not pop it on any carbon seatposts though.

So far, so good. Actually fitting the backpack to the mount can be a bit of a fiddle: steady the bike and keep the catch open with one hand, and slide the backpack on with the other. As the backpack is not completely rigid, it can take a few attempts. You may need help if you plan on mounting the backpack with the rain cover on, unless you have more hands than I have - you'll need at least one extra one to keep the cover out of the way of the attachment housing.

Backpack fitted, it's time to jump on the bike. Remember, if you mounted it vertically, to either swing your leg higher, over the front, or over the front triangle. I kept forgetting it was there when dismounting and kept hitting my wet and dirty cycling shoes on the shoulder straps.

When mounted horizontally, there's not much chance of forgetting it's there as it sits so close to the seatpost that I could feel it with every pedal stroke. I tried it for a few hundred metres and gave up. Lucky that the mount system swaps between horizontal and vertical really easily.

Another disadvantage of the horizontal position is that the stuff you carefully organised in all those compartments will slide out, and not be so organised anymore.

Mounted vertically, it works better. It sits reasonably close to your back, but not so close it annoyed me. The mount itself, however, did. It's chunky and wider than the nose of the Brooks Swift I sat on, and though it didn't get in the way, I could feel its presence with every stroke. While the bike felt noticeably top-heavy before jumping on, while riding it was still noticeable, but less pronounced - not really an issue.

Both the backpack and the cover have enough reflective detailing to be seen in the dark. The backpack also has a little strap to mount a rear light on; sadly not usable with the cover on as it disappears inside it, though your rear light can still be seen through the cover.

As a backpack it's OK for carrying short-ish distances. From a subjective point of view, the formed frame makes it look and feel a bit too much like a laptop bag for my liking - I didn't really like the look, or the feel of it on my back. The mount attachment, with the special cover on, can be felt, but not uncomfortably so. I found the shoulder straps a little on the short side, which may be an issue for those built like Michael Phelps. You get a height-adjustable chest strap, but no waist strap.

For the price of the Union 34 with seatpost mount, you can get a decent rack and pair of front panniers; or a backpack for much less. It will depend on your typical journey which makes most sense.

Verdict

Seems a good option for those switching between cycling and walking, but doesn't really deliver on the promise.