JRitt@essex

Hello and thanks for the question! It was a good idea, but has some issues that I addressed in a different thread when the same question came up previously. Below is what I wrote. Please let me know if you have any other questions and thanks again!


We don't have a caliper that would work with the ST carbon ceramic discs (which are the same dimensions as the OEM discs). There are several reasons why our calipers are not compatible. OEM-style discs tend to have a very tall radial depth, as does the pad that mates to them. Radial depth means the distance from the inner diameter of the disc to the outer diameter...essentially, the height of the swept area. For example, the iron OEM GT3 discs have a radial depth of 66mm. The PCCB's have a swept area that is 75mm. That is typical. Unlike a proper iron racing rotor, carbon ceramic discs typically do not have an efficient internal vane structure that flows a lot of air. For example, our iron front discs have 84 internal cooling vanes. Implementing such a design on a carbon ceramic disc would be both technically challenging and expensive/labor intensive. The OEM PCCB discs have about half as many, and they are not the same shape. Since they don't flow nearly as much air, Carbon ceramic discs (and their corresponding pads) are usually made to have as much surface area as possible to aid with the radiation of heat. That's why on just about every model of car that is offered with both iron and carbon ceramics, the carbon ceramics are considerably larger and have a larger radial depth. Conversely, our iron racing discs are incredibly efficient, and can be made with a smaller radial depth. In our case, the radial depth of our iron discs is 54mm. AP Racing doesn't have a caliper in its part bin that would run on a disc with a radial depth as large as the OEM setup. Doing so would mean that the caliper and pads were carrying around a whole bunch of unnecessary mass (as we see with the OEM setup). The efficiency of our setup allows us to remove a nice chunk of mass from an iron disc, while still supplying plenty of thermal capacity.

At this point we've dealt with carbon ceramic discs in many markets...C6 and C7 Corvette, Camaro, Audi R8 and TTRS, Ferrari, Lamborghini, and Porsche. We have several customers who tried running carbon ceramics on their fleets of exotic cars. They found that our iron discs are the only sustainable option for their cars, which are run all day on the track. The cars were constantly down for service, and the running costs of pads, disc, and brake fluid replacements were astronomical. While the carbon ceramic technology has improved, the story remains the same across all markets...carbon ceramic discs and track use are not a match made in heaven. At some point that will almost certainly change, but we are not there yet, and we are not comfortable recommending carbon ceramic discs to our customers for track use. We don't believe that current carbon ceramic technology can match iron in the track environment. Yes, the ccm discs are lighter, but they run hotter and don't have the same durability. They most certainly don't have the same long-term running costs. Our iron competition systems have been proven over millions of miles at all levels of pro motorsports, and we believe that they offer the best blend of performance, weight, and long-term running costs. If money is literally no object and you don't mind throwing piles of it at the car, then yes, carbon ceramic discs are an option to save every last pound. Ninety nine percent of customers have at least some cost consideration however, so it's not a recommendation we make or promote.

Below are some comments from our website on carbon ceramic discs:

Carbon Ceramic is NOT Carbon/Carbon

At this stage you may be saying to yourself, "But I saw that the XYZ professional race cars were running carbon brakes at the track." The carbon brakes currently being used in professional racing are carbon/carbon (abbreviated C/C), which is actually a different material vs. the carbon ceramic discs used on road cars. The carbon ceramic brake discs on road cars are a Carbon Ceramic Matrix (CCM). In recent times many professional racing series (F1, ALMS, IRL, etc.) have switched to carbon/carbon brake discs in an effort to reduce weight. Carbon/Carbon is an outstanding lightweight material for racing, but requires heat before it starts to generate usable friction. As such, they're completely ill-suited to a typical morning commute in a road car!

Iron vs. Carbon Ceramic Brake Discs

In the past few years, Carbon Ceramic brake discs have become increasingly popular on high-end sports cars as either standard equipment or as a factory installed option. Although expensive, they're a great choice for a car that is used exclusively on the street. They save a large amount of unsprung weight, they don't generate much brake dust, have low NVH, and they may even last longer than the rest of the car! For the avid track enthusiast however, they're typically not the best choice.On the racetrack, repetitive stops from high speeds generate considerably higher brake disc temperatures vs. what could ever be legally or sanely achieved on the street. Various manufacturers producing the current crop of carbon ceramic discs claim to match iron disc durability on the track, but our experience tells us otherwise. While they may be less resistant to warping or deformation at repeated elevated temperatures, the biggest problem with carbon ceramic discs is that they tend to oxidize at track temperatures, showing rough surface eruptions on the disc face. In some cases the oxidation is terminal (chopped fiber discs), and the discs must be scrapped once it occurs. In other cases (continuous fiber discs), the discs can be resurfaced, but only a limited number of times and at a cost that would be higher than buying brand new iron discs. Most carbon ceramic discs are measured in terms of minimum mass, rather than the traditional minimum thickness used to measure iron discs. Once the minimum mass is reached, the carbon ceramic disc is typically trash. Below is an oxidized carbon ceramic disc that was driven on a racetrack ten times. Notice the dark spots in which the surface is flaking off / eroding. When your disc looks like this, it has become a $2,000 paperweight![img]https://www.essexparts.com/storage/wysiwyg/C7Z06 CCM after 10 days track sample.jpg

Other Potential Pitfalls with Carbon Ceramic Discs:

• Low airflow- If you look at a specific car model that offers both iron and carbon ceramic discs as an option, the carbon ceramic discs will almost always be considerably larger in overall dimension, with a specific emphasis on a tall radial depth (distance from outer disc edge to inner disc edge). Whereas an iron disc uses a web of directional internal vanes to speed airflow through the disc, most carbon ceramic discs rely primarily on their large surface area to radiate heat into the air surrounding the disc. Hence, the tall radial depth.
• Expensive and limited range of compatible brake pads- There aren't many brake pad options with carbon ceramic discs. The pads must be compatible with the specific disc material being used, and if they aren't, they can destroy the discs in a hurry. Since brake pads are a very personal choice to most track junkies, carbon ceramic discs don't provide many options for the driver to chase a desired feel. Also as noted above, carbon ceramic discs tend to be very tall radially, which means very large brake pads are required. In the world of brake pads, price is usually directly proportional to size: Bigger = more expensive.
• Poor feel- Experienced drivers will tell you that cast iron discs provide superior pedal feel due to less compress-ability. Some drivers find that carbon ceramic discs feel soft or abrasive at lower temperatures, but feel like stone with little modulation once they heat up. Feel and the resulting confidence is rather important when hurtling towards a guardrail at 150mph!
• High replacement disc cost- Carbon ceramic replacement discs can be hideously expensive. If you do wear out or damage a disc, it can cost thousands of dollars to replace or resurface them. When running carbon ceramic discs hard on a racetrack, the odds of having to replace one or more of them increases exponentially vs. if you only drive your car on the street.
• Damage-prone- Many manufactures suggest covering their carbon ceramic discs when handling them, so they are not chipped or fractured. One knock when changing a wheel can destroy a disc. Additionally, some chemical wheel cleaners or abrasives used in car detailing can damage carbon ceramic discs.
• Splinters- Carbon ceramic discs shouldn't be handled with bare hands, as they can leave carbon splinters in the skin.
• Greater sensitivity to burnishing/bedding-in- Most manufacturers have an explicit, and sometimes intricate, set of instructions for bedding-in their carbon ceramic discs. Iron discs can typically be prepared via a simple series of stops from 60-80 mph with the brake pad of choice.

Iron Disc Benefits

So what can AP Racing J Hook iron discs do for a car previously equipped with carbon ceramic discs?

• Increased airflow and slower heat transfer to other brake components- AP Racing J Hook discs have a unique, high-count vane design that promotes airflow, heat evacuation, and rapid cooling. They don't rely on a large surface area to cool via radiation. The iron discs will move more air than your carbon ceramic's, and as a result they won't heat your brake pads, caliper pistons, and brake fluid up as quickly. You'll be able to run longer sessions without brake fade, and you'll enjoy the confidence that comes along with them. They'll also make any brake ducts that you have on the car more effective and useful.
• Huge range of compatible brake pad compounds- Iron discs will open up a much greater range of available brake pads. You'll be able to achieve a different feel, and tailor your brake setup depending on your needs and environment, whether that is running an AutoX or the most demanding racetrack in your area. You'll also likely be paying less per brake pad set than you were previously, and your pads will last longer.
• Inexpensive spare discs- You'll no longer have to spend thousands of dollars when it's time to replace your discs. AP Racing J Hook's typically only cost $300-600 per iron disc ring, so you won't have to stress about anything happening to them. They're inexpensive enough that you can always keep a spare set on hand, so you won't have to worry about any brake-related downtime when you're out at the track.
• Durability- Iron discs can take a beating. You can stash your spares in your race trailer, and you won't have to worry about handling them, covering them, dinging them, or chipping them when changing your wheels.

As you can see, although iron discs do come with a slight weight penalty, they're still the smart choice if you run your car hard on the racetrack. They're the obvious solution that has been proven countless times on tracks around the world, at all levels of motorsport.. AP Racing J Hook Discs have been proven time and again in professional racing, winning many races and championships (ALMS, Rolex, Grand Am, etc.).

Jon70

JRitt,
Thank you for the detailed and informative response. I have a specific question regarding weight, on your website you state the front brake package is 15 lbs lighter than OEM and the rear brake package is 18 lbs lighter than OEM for a combined 33 lbs. However, in this thread:

https://rennlist.com/forums/991-gt3-...t-finally.html

You mention:

Front
OEM iron front disc= 24.2 lbs.
OEM PCCB front disc= 15.1 lbs.
AP Racing iron disc in our Radi-CAL front system= 21.5 lbs.
OEM front caliper weight= 9.3 lbs.
AP Racing front Radi-CAL weight= 6.2 lbs.

Rear
OEM iron rear disc= 24.0 lbs.
OEM PCCB rear disc= 13.5 lbs.
AP Racing iron disc in our Radi-CAL rear system= 19.1 lbs.
OEM rear caliper weight= 7.5 lbs.
AP Racing rear Radi-CAL weight= 4.85 lbs.

According to the above data, the weight loss is 26.7 lbs not 33 lbs unless I’m missing other components or info.

JRitt@essex

Good question! The OEM pads are considerably heavier than the ones in our kit. I just threw the front and rear pad boxes for our kit on the scale vs. the OEM front and rear and the difference nets out at about 5 lbs. (this isn't the most precise measurement with the packaging, but gets you close). We've actually had a few customers verify the total corner weight difference on their own scales at home or their shop, and it comes out in the 32-33 lbs. range.

Jon70

Thank you for the clarification. I assumed I was missing something.

JRitt@essex

No worries. I need to go back and change that so others aren't confused. Thanks for bringing to my attention!

Mech33

To be fair, you do get more brake pad material with that increased OEM pad weight.

mdrums

I noticed that too with the Ferodo DS2500 and DS1.11 pads I tried out on my 2017 Carrera GTS compared to stock pad thickness and Pagid Yellow pad thickness. Stock and Pagid were thicker.

I want a brake system with pad thickness like the 991 Cup has...its like the pads are thick as a brick. ;-)

usctrojanGT3

Yeah, like any of us are good enough drivers to feel that difference in unsprung weight. The ones that do track the cars and they don't want ceramics. Tell me why the race teams don't use ceramic rotors?

CAlexio

Cost, and regulations principally.

mdrums

Race teams have follow a rule book which specifies stock rotors or steel depending on race series.