Most commonly, brake rotors are made of Iron. There are some exceptions though. For example, there are some very high-tech rotor materials that are beginning to become more prevalent such as carbon fiber, ceramic, and the like. And in some cases, automotive brake rotors are made of multiple pieces that are comprised of different materials that are joined together as a brake rotor assembly. This is most often an aluminum brake rotor hat, that is bolted to an Iron-based rotor ring. These material and design choices are made to save weight, deal with wear or temperature better in high stress situations like racing, or myriad other reasons that are beyond what a typical vehicle requires when it comes to brake rotors.
With that said, we will focus mostly on iron-based rotors for this conversation, since it is far and away the most common material used in brake discs. Iron itself is a great material for brake rotors due to its ease of manufacture and its overall durability when it comes to wear resistance and tolerance to heat cycling. But it's the mixture of other materials into the iron that really makes the difference, often described as an alloy.
At Sparta we manufacture our brake rotors out of one of two different proprietary iron blends. (Meaning our own unique recipe of herbs and spices)
Sparta’s GX3.0 iron alloy is a fantastic all-around material for this purpose. We arrived at this blend because we were seeking an ideal material for daily driving, heavier loaded vehicles like pickup trucks and service vehicles. The GX3.0 excels at these uses due to its nature of being a very high-quality grey iron that is robust, accepts temperature swings well, and has low wear properties. Overall, this iron alloy is quite like the OEM specified materials, just with extended tolerance thanks to our alloyed blend.
Sparta also developed our CX3.5 high carbon iron blend most often used for more spirited driving, or to help reduce brake noise issues more common with European cars for example. The iron used to formulate our CX3.5 is having carbon flakes added to it in precise amounts which is primarily for noise suppression. As harmonic vibrations pass through the material with varying densities the material helps to dampen these harmonic sound waves. This is similar in result to noise cancelling headphones. High Carbon iron blends are often leveraged on vehicles where the suspension components are more likely to generate noise.
There is some misinformation out there about high carbon iron being significantly better for a brake rotor material, but the truth is, the use of the vehicle should really dictate the material selection. There are always tradeoffs, and in this case, a high carbon brake rotor may perform better in a motorsport application but will wear more quickly than a non-high carbon rotor. So, you really need to match your rotors to you intended use.
Where to find each formulation
Within the Sparta family, you will find that we use our GX3.0 in all our GP1 and GPe brake rotors, as these are most often used for street and mild spirited driving. Then we utilize the CX3.5 material in our Heavy-Duty rotor range, as well as in all our two-piece brake rotor applications, including our GP2, GPX and in all our Big Brake Kits due to the added stresses that these brake systems will encounter.