The integration of a carbon leaf spring into the design of a saddle is unique.
Realising such a difficult concept is a considerable feather in the cap for Frome-based Fabric, a division of Charge Bicycles, and a comparatively niche brand, armed with the vision and ambition for such a project, and able to call upon the not inconsiderable resources of nearby Airbus. The link between bicycle and aerospace engineers? Cycling.
Industrial designer, Ian Redfern, Fabric’s lead on the ALM saddle, estimates the cost of the finite element analysis work carried out by Airbus in the hundreds of thousands of pounds, but when the men conducting it are cyclists, and eager to see a design realised in less than the 10 years of testing compulsory for aircraft development, the terms change.
The best design offers a seamless union of form and function. Fabric’s starting point was to create a carbon saddle in which the rails were an extension of the top profile, rather than separate entities located in bosses at nose and tail - the solution used by Fabric's competitors. Such a design would guarantee flex at the centre of the saddle and, with it, comfort. This they had discovered by chance.
When trials rider Chris Akrigg visited Frome to shoot a video using Charge’s Scoop saddle, Redfern and his colleagues noticed the amount of flex at its centre as he pedalled on a turbo trainer. They had previously believed the Scoop owed its comfort to its shape. Generating flex at the centre of a carbon saddle, however, is a more significant challenge.
Place a cutaway at the centre of a carbon saddle and the result is counterintuitive. Redfern explains: the surrounding area then requires reinforcement with carbon ribs. The result? A stiffer saddle, rather than one that relieves pressure.
While the functional advantages of integrating a leaf spring to guarantee flex had become obvious to Redfern and his colleagues, early consultations with carbon specialists from one of the world’s biggest bike brands suggested it couldn’t be done.
Undeterred, Fabric returned to Airbus, partners on a previous project to 3D print frame dropouts. The saddle project would be still more sophisticated. This time, the Additive Layer Manufacturing process (from which the ALM saddle takes its name) would be used to print titanium rails equipped with what Airbus described as “hyper-pins”.
“When we first spoke to Airbus, they said they could help us with the carbon lay-up. They also told us about a new technology that they were developing called a hyper-pin: essentially, barbed pins like those you would find on a fish hook,” Redfern explains.
“When Airbus develops a new concept like the hyper-pin, it has to be tested for ten years before it can be used on an aircraft. The idea was that they could print the saddle rails in titanium and at the same time print tiny pins on them, and ultrasonically bond them to the carbon saddle: essentially, by hitting the carbon with an ultrasonic wave until it just about breaks up, and then forcing the barbs into the carbon, so it almost seals around them.
“Airbus had this new technology that they were keen to explore and develop and we thought, 'This is amazing. We’re going to make something that no one else can make: no other bike company has contacts who are doing this, or have this manufacturing capability'.”
The 3D printer owned by Airbus, unsurprisingly, is cutting edge, able to discharge titanium particles at an accuracy of 0.1 of a micron. After 36 hours of printing, a set of twelve rails, complete with hyper-pins, was produced. A further twist in the tale was to come, however.
Convinced of the merits of looking beyond the bicycle industry, Fabric sought a manufacturing partner in the Far East with expertise in other sports, arriving at the door of a firm which for the last twenty-five years had made tennis rackets, golf clubs, and ice hockey sticks. Their experience with golf clubs was considered especially pertinent: items made by uniting a carbon shaft with a titanium head. The manufacturer, however, had another, better idea.
“We went to see them, showed them the design with titanium 3D-printed rails, and they said, ‘Oh, we can make that in carbon,’” Redfern remembers. The original idea would be realised, with Airbus' influence retained in the carbon lay-up.
The Far Eastern manufacturer now produces sixteen of the saddles each day. Even with the considerable resources of mass production, the Fabric ALM saddle remains a high-spec, low volume item.
Two options are available: the ALM Ulimate with a vacuum-bonded cover, and a limited edition cover made from buffalo leather. Prices from £225.