Design

One of the unique benefits of carbon fibre is that different types of fibre can be placed in varying orientations within a frame, putting strength exactly where its needed. Using Finite Element Moulding to visualise the loads on frames on computer, we can experiment with different materials, layups and structures without having to build numerous physical prototypes. With FEM, we can simulate the loads from riding and see exactly how those loads will affect a frame design. This step is essentially Finite Element Analysis (FEA), which not long ago was state of the art. FEM goes further, though, allowing us to add, remove or change material and refine the design virtually, testing as we go along. Once a frame design is performing as we want it in FEM, we know it’s worth making a physical prototype for real-world testing. Working this way saves both time and money, and money saved by us means more affordable bikes for you.

Most carbon fibre frames look smooth and seamless on the outside. What’s important, though, is what they’re like on the inside. The conventional air bag moulding process, using inflatable bladders inside the frame to press the carbon and resin into the moulds, can result in ripples or even folds on the internal walls of the tubes which, in some cases, can lead to delamination or premature stress fracturing – every irregularity is a potential stress riser. To avoid these issues, we use our Glide-Tech process. In conjunction with the EPS Moulding System, we get internal surfaces as smooth and wrinkle-free as the exterior. This increases strength due to the uniformity of the fibres, and greater strength allows us to use less material for a lighter frame. Just to be sure, we use tiny fibre optic cameras to inspect frames internally after production, ensuring that there are no wrinkles, no excess material and no moulding residue.

Making a carbon fibre frame involves compressing layers of carbon weave and epoxy resin into a mould to get the desired shape. Traditionally, inflatable bladders are used inside the frame to force the material into the mould, but because the shape of a bladder can’t be finely controlled there can sometimes be wrinkles or inconsistent thickness in the finished frame. To avoid this, we use expanded polystyrene – essentially the same stuff that helmets are made from. We can make EPS formers to the exact shape that we want before laminating carbon fibre around them and placing the whole lot in a mould. When heated, the individual beads in the EPS formers swell. Out in the open they’d reach 40 times their original size, but constrained by the mould they exert pressure on the inside of the carbon fibre, pushing it into exactly the desired shape with consistent thickness and no wrinkles. The result is a lighter, stiffer and more consistent final product.

Just as there are different alloys of aluminium and steel, so there are numerous types of carbon fibre. So many, in fact, that knowing that a frame is made of “carbon fibre” really doesn’t tell you very much. For the rider, this can be a problem – you can’t tell exactly what kind of carbon a frame’s made out of just by looking, even if there’s not a layer of cosmetic weave or paint on it. The lighter a frame is, the stronger the material has to be. All SwiftCarbon bikes use a combination of T700, 800 and 1000 filaments from Toray in Japan, the world’s largest producer of carbon fibre – most of it is used by the aeronautical and defence industries. We also use filament from Mitsubishi Rayon, with the combination of Toray and Mitsubishi carbon fibre helping us to deliver the superior ride quality of every SwiftCarbon bike.

Carbon fibre isn’t just carbon fibre. Woven carbon filaments by themselves aren’t very useful. What turns carbon fibre from floppy sheets to stiff, resilient frames is epoxy resin. The resin binds the layers of carbon fibre together to form a composite structure – really they should be called carbon/epoxy frames. We use Carbon Nano Tech (CNT) reinforcement in the resin for our frames and wheels. These molecular-level cylindrical structures can strengthen the final product significantly, but success with nanotubes relies on careful manufacturing. It’s easy for the tubes to clump together, leading to inconsistent material properties. Our construction technology gives us precise control of the distribution of resin in the carbon layers, ensuring that the nanotubes can do their job – giving a stiffer and more durable frame.