FFWD DARCtm technology is short for ‘Double Arc’ which refers to the profile of the rim. The revolutionary DARCTM profile improves aerodynamics dramatically by reducing the drag. Air has the characteristic to stick to its surface and by cre¬ating a negative arc section the air will be compressed more at the positive section. This will increase the pressure just like on the topside of an airfoil. Increased pressure results in a faster airflow and less resistance on the wheel which reduces the drag. The DARCTM profile is applied to the F6R Clincher, the F6R tubular and F9R tubular rims.
We use High-Tensile TC-35 carbon for the majority of the lay-up. This gives the rim a very high strength with sufficient stiffness to cope with hard application of the wheels. So, rather than use a stiffer, but more brittle carbon type, we chose durability over ultimate stiffness. In some lay-ups we add some higher modulus sheets to increase stiffness locally.
We actually use multiple layers of different types of carbon. Only the outer layer is made from a 3K weave. Underneath this layer are layers of UDF (Uni-Directional Fiber) sheets. A mixture of different angles to resemble a uniform material. Because carbon fiber can handle tension very well, we have to mix up the layers to make the rim stiff and strong enough. Pressure is not a great feature of a fiber. Just think of a string being pushed ). But when mixed correctly, the different angles interconnect through the resin to make it resistant to all kinds of forces .
The 3K has a slightly lower stiffness/weight ratio than UDF (Uni-Directional Fiber) sheets of equal fibers, but it makes up by giving the rims a bombproof feature. Why? Because when a strand (or multiple) gets cut in UDF, by crashing for instance, the sheet is compromised and the tear will expand through a larger part of the sheet at continuous workload. A weave will stop the tear because it is intervened by the crossing layer of strands .
Although it is not advised to ride with a 'hole' in your rims, situations can occur where you might not know of a damaged rim or it is not an option to stop right away. Then you have the extra safety of the 3K weave to get you home.
All rims are molded with a process we call Ecomtm (Equal Compression). This means that the rims are molded with a custom-made air bag that has the inner shape of the rim. This makes sure that the pressure/compression is equal on the entire inner surface of the rim. Result is a practically void less rim section and a smooth wall on the inside of the rim. Without voids, the carbon sheets are completely fused into one system. The rim structure is much better and you can make the rim lighter and stronger.
Ecomtm also provides for a smooth inside (no wrinkles!) which is a great feature and not common for carbon rims. This is for instance very beneficial for the nipples. Just imagine how the force of the spoke tension is applied through the nipple seat onto the rim itself. If the nipple seat isn't smooth, the transition of the force isn't clean and optimal. This might cause spoke, nipple or spoke hole failure in future. FFWD rims are made with Ecomtm which ensures longevity.