Like this site? Help us to make it better.


Union 34 Seatpost Mount Bag and Quick Release Seatpost Fixing System



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

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

What the scores mean

Good scores are more common than bad, because fortunately good products are more common than bad.

  • Exceptional
  • Excellent
  • Very Good
  • Good
  • Quite good
  • Average
  • Not so good
  • Poor
  • Bad
  • Appalling

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.


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

Make and model: Union 34 Seatpost Mount Bag and Quick Release Seatpost Fixing System

Size tested: n/a

Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?

This is what Union34 say: "A stylish luggage solution for seamless transitions from foot to bike. The Stripe Seatpost Bag fixes onto a seatpost fitting for security and balance as you ride, the unobtrusive mount sits flat against your back for comfortable carriage on foot.

Packed with smart space saving compartments and a padded laptop sleeve, the Stripe rucksack has room for everything you need for work, study and commuting. It fixes quickly and easily to the seatpost mount with reflective details for added visibility on the roads. When the cycling leg of your journey is over, un-clip it and sling it over your shoulders with the wide, padded shoulder straps.

With a range of pockets and a padded laptop sleeve, it's perfect for style concious urban cyclists."

Tell us some more about the technical aspects of the product?

o Fits the Union 34 seatpost mount (sold separately)

o Wide, padded shoulder straps

o 15.6" Laptop sleeve

o Durable 600dn water resistant fabric

o Reflective details

o Reinforced handle

o 30 Litre capacity

Rate the product for quality of construction:

Though the bag looks well-made, and has some good features, like two rubber feet, the zips are own-brand. The bag has stood up well to use so far, though it doesn't look or feel as sturdy as other bags I have used.

Rate the product for performance:

It's not that easy to get the bag on and off the bracket; almost impossible with the rain cover on unless you've got more than 2 hands. In the upright position, the bike feels top-heavy, in the horizontal position, the bag slides too far forward. The bracket is wide and can be felt on every pedal stroke.

Rate the product for durability:

As above, it's definitely not in the Carradice or Ortlieb class of durability.

Rate the product for weight, if applicable:

The bracket alone weighs 795 grams, you can get full-size pannier racks that are lighter than this. The backpack weighs nearly 1.5kg, that's more than twice the weight of an Ortlieb front pannier. Saving weight is not a good reason to choose this bag.

Rate the product for comfort, if applicable:

As a backpack, it's OK, as long as you remember to use the blanking plate. On the bike, the horizontal position is not really usable, and the vertical mounting option makes the bike feel top-heavy.

Rate the product for value:

At over £100, you can get a decent pannier rack and a pair of Ortlieb front panniers for the same price. Granted, they won't work as well as a backpack, but they'll easily outlive the Union 34, pack more and work better on the bike.

Tell us how the product performed overall when used for its designed purpose

The Union 34 is one of those products that seem like a great idea on paper, but doesn't work as well as hoped in real life.

Tell us what you particularly liked about the product

I really like the idea of a backpack that you can clip to your bike when riding to avoid arriving at the station with a sweaty back.

Tell us what you particularly disliked about the product

The fiddly mounting.

Did you enjoy using the product? Not really.

Would you consider buying the product? No.

Would you recommend the product to a friend? No.

Anything further to say about the product in conclusion?

Looks like a good idea on paper, but doesn't work as well as you'd hope.

Overall rating: 5/10

About the tester

Age: 32  Height: 1.78m  Weight: 76kg

I usually ride: All of them!  My best bike is: Cervelo Dual

I've been riding for: Over 20 years  I ride: Every day  I would class myself as: Expert

I regularly do the following types of riding: time trialling, commuting, touring, club rides, fixed/singlespeed, Audax


Add new comment


Chan73 | 10 years ago

Like many people who commute, I've tried every option and so far the best is without doubt a rack and bag or panniers ... but they don't look great and if you want to take off the rack for a winter training ride then its a bit of hassle removing it.

So, whilst searching for the best seat post bag option I came across the union 34. It seemed to be the perfect option. I couldn't pay the big bucks so I did find an amazing deal for the bag, seat post and delivery so thought it was worth a punt

First impressions when it arrived is that its a solid seat post clamp and a well made, well thought out bag.

I've only had 1 test ride so far for a few miles but its impressed me enough to write a review. I think this is the best bike bag I've ever used.

Once the seat post is fitted, which takes only a minute and locks on solidly, attaching the bag at first was a bit fiddly. I moved my seat forward about 5mm to allow more clearance and that made life much easier. Once on, it sits solidly.

I think its quicker to attach than a bag to a rack (using clips or velcro), holds a lot more, is extremely well thought out regarding layout inside and pockets outside.

I went across a good few bumps carrying a heavy Kyptonite U lock and clothing and didn't feel any movement. When I arrived at my destination it was great to slide it off and sling it over my shoulder to head to the pool. I also got out out of the seat to drive up a few hills and I didn't really feel like the weight made the bike off balance ... no more than a bag attached to rack.

The seat clamp does sit wide on the seat post, and it catches minimally on your inner thigh at one point on the downstroke but because its very round and smooth its not an issue.

I'm really impressed, and if you can get a deal on this like I did (or money is no object and you pay full price) then I would say that without doubt you should go for it if you want a good looking, robust, clever bag.  41

As a final note, I use this on a Canondale CaadX 2014

a.jumper | 11 years ago

Crazy price! Two bungee straps (one over, one under) will quickly and easily attach most A4+ semi-rigid backpacks securely on top of a common pannier rack.

Dr_Lex replied to a.jumper | 11 years ago
a.jumper wrote:

Crazy price! Two bungee straps (one over, one under) will quickly and easily attach most A4+ semi-rigid backpacks securely on top of a common pannier rack.

Absolutely, or to something like a Topeak top rack if there are no mounting points for a standard rack.

Latest Comments