Auto Brake Pads, Brake Parts Wholesale
by Jeff Ritter
One of the most common debates we see raging on high-end sportscar forums today is carbon ceramic vs. iron brake discs for road and track cars. This debate has been playing itself out over many months and years, with proponents on both sides of the argument fiercely defending their viewpoint. Since carbon ceramic discs are typically an $8,000+ option, the financial stakes are high, thus dictating that the emotions attached to the iron vs. carbon ceramic decision run hot as well.To put it simply, nobody wants to be the guy who made a five-figure mistake!
The purpose of this article is to first explain the differences between the three main types of brake discs on the market today. After examining the technical differences and limitations of each disc type, we will then consider what you can do to ensure that you have the brake system on your road and track car that best matches your intended usage.
While the complete materials science and design parameters behind each disc type is far outside the scope of this article, we will first take a brief look at what exactly is being compared before getting too deep into the merits of choosing any single disc material.
A brake disc is a fairly simple implement in the grand scheme of automotive components. Its job is to transform the kinetic energy of the car’s linear motion into heat when clamped by the brake caliper and pads. The material used for a disc’s construction must have the capacity to absorb and dissipate heat, while also having enough mechanical strength to handle the clamping force of the caliper and the brake torque. It must also transmit an appropriate and controllable amount of friction as it interfaces with the brake pads. That is clearly a big ask, which is why we have such a limited range of materials that are up to the task. For automotive applications, there are three primary types of brake discs:
Gray iron brake discs, which earn their name from their graphite content, gained widespread automotive use in the 1960s.While you more frequently see the term ‘steel’ used to describe the gray iron brake discs most of us have on our cars, that is not the proper word to describe them. They have remained popular for so long because we have yet to find a material that offers a superior blend of performance, durability, and cost. Iron discs have excellent thermal conductivity, mechanical strength, wear resistance, and can be manipulated to meet specific needs via alloying and easily forming into different shapes. Small amounts of other elements such as carbon, molybdenum, and silicon can be added to the mix to tailor the performance to meet specific needs, making iron discs especially versatile. The processing costs of casting and machining iron brake discs is relatively low vs. other disc materials, making them cost-effective for broad use on a wide range of applications.
Carbon-carbon (C/C) brake discs are primarily used in aircraft brakes, with extremely limited use in certain automotive racing series such as Formula 1 and IndyCar. The key reasons for their usage in these applications are low weight, thermal shock resistance, low thermal expansion, ability to withstand very high temperatures, and a high coefficient of friction at elevated temperatures. To form a carbon-carbon disc, fiber fabric is first laid-up in the general shape of a disc (aka a preform). The fibers can either be chopped, or they can be woven into layers (sometimes referred to as ‘continuous strand’). The disc preforms then go through a series of processes such as heating in an inert gas, chemical vapor deposition (CVD), and/or liquid phenolic impregnation (LPI), with the goal of creating a pure carbon structure. Uniquely, the pads that mate to carbon-carbon discs are made from the identical material. These processes are complex, time-consuming, and extremely energy-intensive, taking weeks to process at extremely high temperatures and requiring very expensive equipment. Logically, they result in an incredibly expensive final product. While they work well when a massive jumbo jet slams on the brakes and instantaneously generates tremendous heat, Carbon-carbon discs are not suitable for road cars because they do not generate adequate friction at low temperatures seen during daily driving, and they also tend to have a high wear rate.If you think that you have a brake dust problem on your wheels now, multiply that by 20 with Carbon-Carbon!
Carbon Ceramic Matrix (CCM) or Ceramic Matrix Composite (CMC) brake discs are a derivative of carbon-carbon discs that are becoming more and more popular on road-going sportscars today. Carbon Ceramic discs are different from carbon-carbon discs because they are manufactured by melting silicon powder and drawing it into the pores of a carbon fiber disc mold at extremely high temperatures. This process of Liquid Silicon Infiltration creates a ceramic matrix, known as silicon carbide (C/SiC). The discs are then coated with a thin layer of material to protect them from oxygen, because oxygen turns solid carbon into carbon dioxide gas at high temperatures. Carbon ceramic discs are superior to carbon-carbon discs for road cars because the ceramic matrix allows them to generate friction at daily driving temperatures. They are also more abrasion resistant to brake pads, and they are less expensive to produce vs. carbon-carbon because of the reduced processing time. That said, the process of creating a carbon ceramic matrix disc is still much more labor-intensive and time-consuming vs. iron discs, resulting in considerably higher costs.
A key point to understand is that Carbon-Carbon and Carbon Ceramic Matrix are very different materials with very different performance characteristics, intended for very different applications.Carbon-Carbon discs used on F1 cars are worlds apart from the black discs that come from the factory on a Porsche 911.Yet, enthusiasts often generically refer to all non-iron composite discs as “ceramics” or “carbons”, just like they mistakenly refer to iron discs as “steelies” or “steels”.
What is the source of this confusion and misunderstanding? Vehicle manufacturers. They perpetually leverage the racing pedigree of carbon-carbon discs to sell expensive optional carbon ceramic brake packages. Their websites, literature, and salespeople use marketing phrases such as, “proven in motorsport”, “maximum durability”, and “racing-inspired” to describe their composite disc brake systems. Unsuspecting enthusiasts assume that if the carbon-carbon discs they saw in a Formula 1 race can handle that type of abuse, then carbon ceramic discs are certainly the ideal choice for track abuse on their ZR1 or 911 Turbo. Unfortunately, they are comparing two completely different product types! While Carbon-Carbon brakes have long been recognized as the ultimate racing brake solution since Gordon Murray first applied them to a Brabham F1 car in 1976, carbon ceramic brakes have not been developed with that intention. They were instead designed with the objective of being the ultimate solution in road brakes.
Carbon Ceramic discs are a great option for street driving because they have the following characteristics:
If the above benefits are important to you and you can afford them, carbon ceramic composite discs should certainly be a consideration when purchasing your next vehicle. While some enthusiasts cannot live with the wooden feel of a carbon ceramic brake system, they can offer superior road manners and performance.
While carbon ceramic discs do excel in street usage, their performance on the racetrack is an altogether different story. On the track, repetitive stops from high speeds generate massively higher disc temperatures vs. what could ever be legally or sanely achieved on the street. Everything below applies to not only OEM carbon ceramic discs, but to current aftermarket offerings as well.
Despite the promise of superior racetrack performance by vehicle manufacturers, the real-world results tell a very different tale. A quick search of Rennlist, McLaren Life, Audizine, or Corvetteforum will reveal a lengthy list of frustrated owners who have been literally and figuratively burned by carbon ceramic discs on the racetrack in one form or another. You’ll find comments about oxidation/burning up, rock chips, wheel interference, difficulty bedding, lack of pad choice, etc. We’ve seen this play out over and over again for the past twenty years since Porsche first brought PCCB to the market on the Carrera GT and 996 GT2. Some internal Porsche personnel have even finally admitted that PCCB may not be the best choice if you track your car!
So, you ordered your latest track car with the carbon ceramic disc option, and now you’re feeling a bit despondent about that decision. Fear not, you have options!
Option 1- Keep your OEM calipers, and replace your discs with AP Racing 2-piece Iron J Hook Discs. Our AP Racing J Hook discs are identical in overall size to your OEM carbon ceramic discs, and will seamlessly integrate on the car.While they will add some weight, they will save you a fortune in disc replacements.
Option 2- Replace your stock brakes with a complete AP Racing by Essex Brake Kit. Going this route not only prevents all the headaches associated with carbon ceramic discs, it also preserves your OEM calipers and adds a long list of additional convenience, longevity, and cost benefits. We offer two types of brake systems depending on how you use your car (Road or Competition), and you can click here to see the differences between the two.
A carbon ceramic disc that was either dropped or hit by a rock/track debris. It is now a very expensive paper weight.
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