Top Tube Bags – Product Design Notes

As the home for Technical Bikepacking Equipment, we want to revolutionise how people experience adventure. We aim to create harmonious partnerships between riders and equipment, allowing them to focus on enjoying their ride and adventure. Our number one core principle is innovation, and we only release a product once it outperforms our initial design goals.

As evidence of this, the new Top Tube Pack range has been two years in the making, from the initial planning and prototyping phase to production. The reason for this? Perfection. Every part, from material choice to the Flip Pack’s Mag-Lock magnetic closure, has been honed and perfected in-house. We have had a lot of help along the way thanks to our R&D Division riders. Lachlan Morton, Josh Ibbett and Gail Brown, plus our other test riders, all have been integral to the testing process. Thanks to their feedback, we have ended up with a full complement of five top tube packs, meeting the needs of every type of rider.

With something as simple, ubiquitous and prolific as a top tube pack, there are a lot of excellent examples already out there, and some are loved by many. However, after numerous detailed conversations with our riders and other experts in the industry, it is evident that every single top tube pack has at least one aspect that compromises overall satisfaction. The fundamental problems found with existing packs demonstrated were:


Wobbling side to side when loaded or knocked by the rider or when the front strap is pulled by the handlebars/stem.

Knee rub

Hitting the pack with your knee is an irritation at best and, at worst, can cause severe pain and stop a ride.

Frame rub

Velcro straps combined with movement made short work of paint jobs.


Many look unwieldy, boxy or disproportionate to the bikes on which they are mounted.


Many designs suffer from water ingress through stitched construction, non-waterproof zips or lightweight materials.

Straps or bolt-on?

 Often two different versions are produced, so many riders must purchase multiples to fit various bikes.

How have we solved these problems?

As with all our products, we aim to create the ultimate solutions. In this respect, our Top Tube Pack is no exception. Taking on board the critical features/problems of existing top tube packs, we set about creating the ultimate version. What we didn’t realise was just how long this process would take. In the end, it has taken over two years and well over twenty different prototype stages (not to mention all the variations and adaptations to each prototype) before we were happy to go to production with the full range of packs now on sale.

Tailfin Top Tube Pack evolution

Curing instability

Without a doubt, the number one issue with all top tube packs is the propensity for unwanted movement. This movement can come from terrain-based vibrations or rider interaction (knocking to the side when getting on and off the bike, for example). Many existing packs fit well when the bike’s top tube matches the pack’s base width, but often need an additional stabilising strap around the fork steerer. They stop working well when it’s either trying to grip narrow-diameter steel tubing or oversized carbon and alloy tubes. Luckily we already had the basis for the solution in the form of our proven V-Mount technology (found on our existing Downtube Packs). The V-Mount system combines many parts, all working together in harmony. From the tacky rubber pads to the abrasion-resistant and grippy TPU straps to the welded V-Mount tunnel/garage to how we transfer the rigidity to the internal HDPE ‘Taco Shell’. It’s the unification of these parts that create the magic. 

We haven’t taken the same V-Mounts from the Downtube Packs and just attached them to the bottom of the Top Tube Pack though. These V-Mounts feature a completely revised design for dedicated use, forming a robust structure capable of withstanding any knocks from the rider, remaining locked in place regardless of riding conditions and terrain.

How to design the best top tube pack

The V-Mounts found on the Top Tube Packs differ from those found on the Downtube Packs in one crucial way. Whilst the Downtube Pack V-Mounts are separate from an internal frame inside the pack, the V-Mounts of the Top Tube Packs are fully welded into the structure of the pack. This not only helps to increase the rigidity of the pack, helping to increase the stability when loaded, but also reduces the height of the pack allowing it to sit closer to the top tube. A further advantage is a reduction in the weight of the overall V-Mount structure. Something we were at pains to do in order to create a fully functional pack within a competitive weight range.

All of this focus on performance has allowed us to create a high-volume top tube pack and still guarantee complete stability even when used on smaller-diameter frame tubing.

Eliminating knee rub

Every rider is different. Through extensive research and body mapping, it was obvious that one of the limiting factors of a rider’s use of top tube packs is the tendency for the pack to interfere with knee tracking. Riders with a narrow stance width or knee tracking that moves inward laterally often have problems, especially when riding out of the saddle or on road or gravel bikes with a shorter reach. Interestingly it was researching and testing this issue that proved to be the most time-consuming. Mainly as we needed a large enough test group spanning all styles of rider physiology and disciplines to ensure effective testing.

Slow motion video capture and anecdotal field testing indicated that if the goal is maximising the amount of storage available, each rider and bike combination has a ‘maximum pack size’ before causing obvious knee rub. Just as with a shoe, glove or even bike frame there is an optimum ‘sweet spot’ in terms of the shape. One size most certainly does not fit all.

The other important take home was that knee rub often occurs with an unstable top tube pack. Any movement of the frame through normal riding tended to displace the top tube pack inducing a side-to-side motion. This is often exacerbated when heavy items such as phones are stored in the pack. When this occurs, even riders with fairly vertical knee tracking can suffer from knee rub.

These observations freed us up to divide the design process into two distinct channels; number one: creating a pack for eliminating knee rub for sufferers, focussing on body mapped shaping (developing our tear dropped shaping to reduce volume where the pack is most likely to interfere with knee tracking) and number two: develop multiple packs of incremental volume that put the emphasis on maximising storage but incorporating the knee rub minimising design.

The 0.8 Litre Zip Top Tube Pack is the pack we aim to be the solution for riders who currently suffer from knee rub. It offers the most clearance and features radical 3-dimensional tapering with a drastic vertical taper designed to find the sweet spot between storage and interference. Combine this with the stability created by our V-Mount attachment, and you would hardly know the 0.8 Litre Top Tube Pack was there.

Protecting the frame

When you combine slippery materials with velcro straps or other inherently unstable attachment methods, you get movement. Put a top tube pack with these features on your fresh new bike frame, take it for a ride and even when riding on dry and clean roads, this movement will eventually damage the finish of your beloved bike. Mix in some rain and dirt, and in some extreme cases, this unwanted movement can cause actual damage to the frame itself.

You could apply lots of helicopter tape to protect your frame or just mount one of our packs instead. How are we so confident of this? Say hello to our very own Wiggle Rig!

The Tailfin Wiggle Rig has been custom designed and built by us to mimic typical rider-induced movements to a bike frame. Built using two sacrificial frames mounted side by side, the Wiggle Rig allowed us to fit and compare each iteration of our top tube pack design as well as compare performance against all the leading packs on the market. With its set angle of movement and ability to run continuously for twenty-four hours a day, we are able to condense the equivalent of a year’s worth of riding into a handful of days.

We were able to identify any damage that had obviously been caused by the movement of a pack at the end of a test period, and, thanks to the camera set up to record any movements, we were able to map and compare movement between prototypes and competitors. To make things even more fun (and cover all aspects of standard riding), we also incorporated moisture and dirt into the test procedures to see if we could induce accelerated wear.

The conclusion after multiple test runs was that our V-Mount system, when fitted with dedicated TPU straps, stops movement completely when attached correctly, even without a front strap.

The difficulties of constructing a flip-top pack and introducing Mag-Lock

From day one we knew we had to incorporate a flip-closure top tube pack in the new range. It’s a style that has huge benefits, allowing quick access to stored items, the ability to see all the contents and providing a guaranteed weather-resistant seal.

The key issues for us were: 1) how to design a functional flip-top shape that could be constructed using 3D welding and 2) no existing closure mechanism met our exact needs in terms of creating a secure and reliable closure.

Welding our signature Hypalon and Ripstop Nylon panels ensures a watertight construction which is why we construct all of our softgoods using this method. The Top Tube Packs needed to be made in the same way. This method is relatively straightforward when creating simple packs, but the tapered shapes and rounded edges of the Top Tube Packs meant that consideration had to be taken to design all angles and radii to perfection in order not to introduce any awkward folds or too tight an angle and in order to keep a clean and good-looking aesthetic. Any miscalculations could lead to weak points in the construction process and produce a messy end product. Anyone who has tried wrapping an awkwardly shaped present in a neat way can attest to how difficult this can be!

How to design the best top tube pack

The design process of the Mag-Lock closure mechanism still brings our engineers out in cold sweats. As the image below demonstrates, this was not a simple process. Dozens of versions have been tried and tested before settling on the final Mag-Lock fitted to all Flip-Top packs. The reason for the development of our own, unique Mag-Lock? We felt all existing magnetic closures available off-the-shelf all suffered from one or more of the following issues: they don’t allow the pack to increase in volume (no stretch), they weren’t particularly glove-friendly, they were made up of non-replaceable parts, they didn’t work well under tension, and, our pet hate, didn’t provide confidence in the pack being truly closed.

As engineers first and foremost we are firm believers that latches and mechanisms offer a better experience when they have a ‘positive action’ – just like the X-Clamps of our pannier bags. What we mean by this is we want these mechanisms to be actively opened and closed; this way you 100% know that the operation has been done.

The Mag-Lock is designed to offer a repeatable closure, be simple to operate even with winter gloves, provide noticeable feedback to eliminate second-guessing, be self-adjusting and user repairable. This last part is of vital importance with this style of closure. We utilised shock cord to allow the pack to stretch but we are well aware that even though this is the best material for the job, it has a finite life span. To counter this, rather than just attach it permanently with glue or stitches we developed a cunning little clutch mechanism that allows for easy replacement of the cord without additional bulk.


Our entire Top Tube Pack range uses a revised, lighter version of Tailfin’s signature Hypalon/Diamond Ripstop Nylon* mix to create a waterproof pack. All packs feature our 3D welded construction process (no mean feat on such a small yet complex design), eliminating any potential weak points for water to get in. On top of this, all zips used are genuine, fully waterproof versions. 

*Due to the lower wear and stresses placed on a top tube pack, we could incorporate a lighter-weight 210D Hypalon material without impacting durability.

How to design the best top tube pack

What about zips?

Zips are often the weak point of a top tube pack, both from a waterproofing perspective and also as they tend to fail over time if a pack is either overstuffed or the angle and support of the zip are not enough to overcome friction introduced when opening or closing the pack. In order to ensure our zips stay reliable for the lifetime of a pack we had to incorporate the following features:

  1. The internal HDPE structure of the pack supports the zip, allowing for easy, one-handed operation.
  2. The V-Mounts hold the pack with enough stability to ensure the pack doesn’t move whilst operating the zip.
  3. The top radius of the pack is constant to ensure even tension throughout the entire length of the zip.
  4. We haven’t removed the secondary metal zip puller to save weight. We found incorporating it alongside our cord pull ensures that the zip is operated at the correct angle and the operator isn’t pulling it away from the direction of the zip.
  5. Most manufacturers opt for a standard No.5 sized zip. We went oversize to reduce failures.


All Tailfin Top Tube Packs can be mounted using the supplied TPU straps or bolt-on attachments with compatible frames. The V-Mount hardware provides two bolt-on positions to place the pack exactly where you want it. In addition, the rubber boots of the V-Mount system are pre-cut to retain and allow the bolts to pass through neatly. Using the V-Mount in this way provides market-leading stability for a bolt-on top tube pack. This also allows for the load to be spread away from the frame’s riv-nuts, minimising any potential damage when carrying heavier loads in your top tube pack.

How to design the best top tube pack

The Tailfin Top Tube Pack also has removable straps; this improves pack life, something sewn-on velcro straps can’t compete with. We also ship all packs with an additional 36cm long TPU strap enabling setup on bikes with a large top/head/downtube union. You can even use two straps together for even larger applications. As we set out to do with all Tailfin products, increasing the number of bikes the Tailfin Top Tube Pack is compatible with.

Combine all of these performance-led features together, and the new Top Tube Pack range can truly be called Technical Bikepacking Equipment. Even on multi-day expeditions in the worst conditions, you can be safe in the knowledge that a Tailfin Top Tube Pack will never let you down.

To find out more about the range, head to the product pages below.