People have been wondering about our disc rotor construction for quite some time now. Hopefully, the following will help. It gets kind of technical. First off, our disc rotors are produced of cast iron steel. For our 2-piece disks, the bell housing (or hat) is produced of duralumin. Google “Duralumin” to get insight on it.
People have mentioned or brought up the idea of “forged” disks, but I’m not sure this exists.
In any case, the most important material in “ferro alloy” is carbon. Ferro alloy refers to various alloys of iron with a high proportion of other elements such as manganese, carbon and silicone. In pure iron, the carbon content is below 0.006%. In steel, the carbon content varies between 0.006% to 2%. And in cast iron, the carbon content varies from 2.0% to 6.67%. The condition of the carbon differs depending on the metal as well.
This cast iron is categorized depending on its specific carbon content and cooling speed. It is categorized into the following types:
(FC) Flake Graphite aka Gray Cast Iron
Most high-quality disc rotors are produced of this. It transfers heat well, cools quickly, and works well with brake pad materials allowing anti-shake. Gray Cast Iron is considered best for high performance disc rotors. Endless disc rotors are produced of this.
(FCD) Spheroidal Graphite Ductile Cast Iron
Ductile cast iron as compared to cast iron is stronger and stretches well. Therefore, it’s used often for suspension knuckle arms. Yet, it doesn’t transfer heat well and doesn’t cool quickly.
(CV) Carbon Cast Iron
This used to be a failed outcome of the FCD, but it’s stronger than gray cast iron. However, it doesn’t transfer heat well, thus isn’t considered ideal for disc rotors.
Normal disc rotor surface after usage.
Carbon content close-up of a normal disc rotor.
Endless disc rotor surface after usage.
Carbon content close-up of an Endless disc rotor.

Endless disc rotors are heat-treated. They are baked in an oven slowly for a number of hours until reaching very high temperatures. It is then baked for an addiitional number of hours consistently at a specific temperature. Then, a couple of more hours to slowly cool down. This step-by-step time process is crucial as it enables heating equally to the core. This helps result in the golden-brownish hue on the surface of certain Endless discs. This “coating” will disappear after initial use and is intended to match the compound for correct bedding procedures and initial set-up. On another note, not only are Japan’s manufacturing skills superior, but the materials they use are much finer. For instance, forged calipers made in Taiwan from manufacturers such as VTTR have decent machining and production quality. Their alumite calipers are, in fact, clean. (I bring up VTTR because there was rumor that Endless produces their calipers there. Not true.). What makes the product inferior currently is the materials used. The quality/grade of FC steel in Japan is much higher in Japan than in Taiwan. And importing this finer material from Japan costs way too much. Also, the machinery in Taiwan is not yet properly “tuned” for the finer material. So, it’s a catch 22. They don’t have the greatest of goods, and if they did, they wouldn’t quite know what to do with it. Last, but not least, their calipers are forged from an aluminum block. This causes unbalanced structural rigidity with “thinner” portions of the caliper being hard and “thicker” portions of the caliper being softer. Endless calipers are produced in a different manner which keeps the entire body balanced and solid. A few things learned from Mr. Inamoto of Endless Japan that I thought I’d share.