Testing the Tailfin way: The story of the SFM

Bringing the latest Suspension Fork Mount to reality has taken months of careful design, prototyping and engineering. At Tailfin we only want to bring new products to market that offer genuine value, improvement or innovation over what has come before.

For the SFM the project brief was relatively simple, “How can we attach gear to a suspension fork?”. The first step in our product development process is always looking for problems to solve, then generating insights highlighting what we need to focus on. We started by fitting, using and testing the majority of products already on the market that attempted to solve the brief. Testing generated the insights regarding the issues we faced, and there were many to overcome. These were some of the problems:

  • The majority of solutions were devised to attach solely a water bottle cage and therefore had a very low load rating.
  • Stiffness, and the benefits it might bring, was largely overlooked.
  • Many would initially grip at first, but since they were manufactured from plastic, they suffered from creep (creep is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses). This meant that they would need constant tightening and would eventually fail.
  • If the mount slipped in to the wheel it could cause a major safety issue as well as causing damage to other components.
  • The strongest solutions discovered were jubilee clips. Whilst incredibly functionally, they had a tendency to scratch, had a poor aesthetic and tended to have sharp edges.
  • The adjustable solutions often ended with a long ‘tail’ that either looked unsightly or would catch. If cut then they also lost some ability to fit other parts.
  • If you wanted to attach multiple items per fork leg, you would either have to double up the mounts or purchase a secondary ‘splitter’.
  • Scratching the fork was a major issue in general.

These were some of the insights/key performance targets for the SFM:

  • Our SFM would be developed specifically for bikepacking, and therefore have a very high load rating to carry gear and water.
  • A high load rating that minimised the chance of slipping would be significantly safer.
  • If slip could be avoided, then in general scratching of the fork would be avoided (for example, you never worry about your stem scratching your handlebars – this is because it doesn’t slip).
  • Stiffness was the key to a high performing mount – the higher the stiffness the better the ride feel and control (similar to how seatpacks wag vs the AeroPack which feels planted).
  • With a high load rating we could offer the ability to mount multiple items at once.
  • We needed to use a band material that didn’t suffer from creep AND was still flexible – this pushed us towards Carbon and Stainless Steel.
So many prototypes!

We then set to work developing, prototyping and but above all TESTING!

Being a product that would be fitted to a suspension fork at the front of a bike we were hyper aware that any potential slippage or failure could be catastrophic. With this in mind prevention of any unwanted movement was paramount, so our testing was based on measuring

In order to identify and improve any weaknesses in our design a testing protocol was devised and a test rig built. Compared to much larger companies that have their own R&D labs, test rigs and seemingly limitless budget, our space and resources are a little on the smaller side. But what we do have are a team of designers and engineers with the talent and knowledge to be able to develop effective and consistent testing. It’s this expertise that is fundamental to extracting the essential data from testing and (in our opinion) is far more valuable than even the most hi-tech test rig.

For the Suspension Fork Mount we wanted to measure how much force it took to move a mount from its original position. This translates to the point in real world conditions when you would either notice the movement, need to readjust and tighten or when the load could affect the front wheel. We wanted to make sure that the SFM at the very least matched the best selling products on the market and ideally a design that beat them in performance. 

The test rig didn’t need to be too complex as the SFM (and competitors) have a very simplistic design and single way of mounting that was easy to replicate. For the test rig we set up a rigid vertical pole to effectively replicate the dimensions of a lower suspension fork leg to which we could mount the adapters. Each adapter was affixed following the instructions supplied by the manufacturer and tightened accurately to the recommended torque settings where given. A Tailfin Cargo Cage was affixed to the mounts at a spacing of 128mm (the top and bottom mounting points of the Cargo Cage). A torque arm was attached to the cage to which a force (torque) measuring device was connected. 

Plan view of the SFM test rig. Mount is fixed to suspension fork lower leg mimic. Force meter is pressed against lever attached to cargo cage.

Force was applied to the torque arm until a slip was recognised in the mount. The angular displacement* was measured and the data recorded. This data was interpreted as a curve of torque against angular displacement plotted and used as a metric to compare mounts.

Fig. 1 Angular Displacement against Torque for suspension fork mounts

Explanation of the curves on the graph (Fig.1)

Starting at 0 on the graph and following the curve up towards the top right; the first straight section of the graph shows how stiff the mount is. The steepness of this part of the curve directly relates to stiffness and a steeper curve is a stiffer mount.

The point where the straight section begins to curve indicates the maximum torque the mount can take before it moves (indicated on the graph with horizontal dotted lines). For the SFM this was slipping, but in comparison, for the same applied force some of the competitors bent. The graph moves from a straight line to a curve at the point where for the same increment in input force, the mount is moving more than it did before. For any torque applied below this point, the mount will return to its original position. Any torque above this point, the mount will need to be readjusted.

The final section of the graph, after the initial change from straight line to curve, indicates the resistance to further movement once the mount has started moving. In the same way as before, the steepness of this section of the curve indicates the resistance to further movement. The steeper the curve, the more resistant the mount is to further movement.

For any Engineers or Material Scientists reading this blog, if you were comparing this curve to a standard material stress-strain curve then the linear section would be considered ‘elastic deformation’ and the curved section ‘plastic deformation’.

The data can also be split to make it easier to identify the differences between mounts as Fig.2 below shows.

Fig. 2 bar charts to indicate Maximum Torque and Stiffness

What can we infer from the results?

Testing is used to validate a design or to indicate where improvements need to be made. By the time we came to this final round of testing we were pretty confident that we had a superior product but testing was still needed to confirm this. 

Looking at the results from the testing it should be noted that both variants of Tailfin SFM performed way above competitors for stiffness and peak torque before any form of readjustment was required. To put it in even simpler terms:

“The Tailfin SFM is more than twice as stiff as competitors”

This translates to gear being more rigid and experiencing less swinging and moving of the carried load as you turn or go over bumps. Stiffer luggage mounts give a more direct feel and less wallowing when turning, leaning or riding over obstacles.

“The Tailfin SFM can take over 3.5 times the torque of the next best competitor before the load moves”

The result? Your luggage will stay where you put it and not go into the wheel/spokes.

It should also be noted that during testing we discovered that if the peak gripping torque is exceeded, the SFM actually grips harder the more torque is applied. It also does this at a higher rate than competitors. This translates to smaller angular slip than competitors if peak torque is exceeded. The real world impact is if it does move you can be confident that it won’t move as far as competitors, therefore the SFM is less likely to go all the way into the wheel.

*Angular displacement of a body is the angle in radians, degrees or revolutions through which a point revolves around a centre or a specified axis in a specified sense.

To keep up with Tailfin’s latest in-depth tech deep dives, product releases like the SFM, plus handy features about bike packing and living with your Tailfin system why not sign up to our regular monthly newsletter?

Blog Post Signup Form
Riding Style