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I just wanted to provide a quick update to this thread now that I’ve had an opportunity to drive my GT4 on track with the Essex/AP brake kit installed. I had the car out at Summit Point Main for a two-day PCA DE and the brakes performed very well. The pedal feel is more firm than the OE setup and the Essex/AP setup requires less force on the pedal to slow the car. I realized after a few sessions that I was able to get the car slowed more quickly using less pedal pressure, as it is much easier to trigger ABS now. As soon as I started to get a better feel for the pedal, I was able to brake more effectively than I had been able to previously with the OE setup and I much prefer the firmer pedal feel and greater sensitivity that the kit provides compared to the OE setup, which I have always felt required a lot of force on the pedal to slow the car quickly.
The calipers and rotors also look great on the car. I don’t think the photos do a good job of capturing how much more purposeful the car looks with these parts installed.
Overall I am very pleased with the performance of the kit and I fully expect that my satisfaction will only increase when the time comes for the first pad change.
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.
You actually only described 1 reason. If there are more, can you elaborate?
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. [...] The PCCB's have a swept area that is 75mm. [...] 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.
Why would the AP caliper need to cover the entire radial depth of the PCCB rotor? Just leave the last 20mm blank.
Have you done a study that the swept area would be too small, or the heat dissipation inadequate?
As you can see, although iron discs do come with a slight weight penalty,
6 lbs per corner (for the discs themselves, not overall). Perhaps I'll do the math later but we know that rotational mass is important.
You actually only described 1 reason. If there are more, can you elaborate?
Why would the AP caliper need to cover the entire radial depth of the PCCB rotor? Just leave the last 20mm blank.
Have you done a study that the swept area would be too small, or the heat dissipation inadequate?
Sure thing. The ST carbon ceramic discs are 380mm, like the OEM iron discs. The OEM calipers are radial mount. In order to fit the AP Racing calipers to the spindle, we use a custom adapter bracket. That necessitates a larger-than-stock disc. The larger disc creates a little space to sandwich the bracket in between the caliper and the spindle. The only way you could just drop the AP Racing caliper on the car and run 380mm discs would be if the mounting hole spacing on the AP calipers was identical to stock. Unfortunately it is not, and you therefore need an adapter bracket.
Also as you noted, the radial depths are fairly different between the OEM discs and the AP Racing discs. Carbon ceramic discs run extremely hot. The internal vane structure of carbon discs isn't nearly as complex as that of a racing iron disc, and they don't flow as much air as iron discs. As a result, carbon ceramic discs are made with a tall radial depth to increase the surface area, in an attempt to radiate more heat and improve cooling.
While I don't have any specific data that I can share, we (Essex and AP Racing) have a lot of real-world experience in this area. Leaving a fairly large unswept area on the lower portion of the disc can lead to problems with cracking. The area that isn't being swept runs substantially cooler than the area that is being swept by the pad, which causes a temperature gradient across the disc. You want the disc to be evenly heated throughout. Having one portion running cooler than the other leads to distortion and premature cracking.
While the unsprung weight savings of carbon ceramic discs is nice, we don't believe all of the negatives of the material are worth that weight savings if you're tracking your car. As noted, carbon ceramic discs oxidize at track temps, regardless of whether they are OEM or aftermarket. In the case of continuous fiber discs (like the ST discs), they can be resurfaced, but at a high cost and a lot of downtime ($2,400+ international shipping and two months of your car sitting while the discs are shipped to Europe for resurfacing...and then shipped back across the pond!). It's much simpler to just buy fresh iron at a lower price and have it tomorrow if required. You also have a much wider range of pad choice with iron, which allows you to tailor the system's feel to your liking. We're seeing lots of comments from former PCCB owners regarding how much better our system feels. Since the carbon ceramic discs run significantly hotter (we've seen a couple hundred degrees F difference on our brake dyno), they're also going to be eating pads and fluid, and putting more wear and tear on everything around them (ball joints, bearings, etc). Carbon discs are also much more prone to damage, chipping, etc.
Carbon ceramics are nice for the street, but the material just isn't on the same level as iron for track use. Someday it may be, but with the current level of technology they still create far too many compromises. I can honestly say that out of the thousands of iron AP Racing brake kits we've sold, I have yet to have a single customer say that they'd rather go back to a carbon ceramic setup.
__________________
'09 Carrera 2S, '08 Boxster LE (orange), '91 Acura NSX, Tesla Model 3 Performance, Fiesta ST
Jeff Ritter
Mgr. High Performance Division, Essex Parts Services Essex Designed AP Racing Radi-CAL Competition Brake Kits & 2-piece J Hook Discs Ferodo Racing Brake Pads Spiegler Stainless Steel Brake Lines
704-824-6030 jeff.ritter@essexparts.com
Sure thing. The ST carbon ceramic discs are 380mm, like the OEM iron discs. The OEM calipers are radial mount. In order to fit the AP Racing calipers to the spindle, we use a custom adapter bracket. That necessitates a larger-than-stock disc. The larger disc creates a little space to sandwich the bracket in between the caliper and the spindle. The only way you could just drop the AP Racing caliper on the car and run 380mm discs would be if the mounting hole spacing on the AP calipers was identical to stock. Unfortunately it is not, and you therefore need an adapter bracket.
I see. So the min. thickness of the adapter and mounting height of the radical caliper requires a minimum disc diameter. The ST discs (per AQ website anyway) are available in both iron and PCCB fitment, and the iron won't work. Presumably the PCCB sized discs are larger. Do you know if they are large enough for the AP caliper to fit?
Leaving a fairly large unswept area on the lower portion of the disc can lead to problems with cracking. The area that isn't being swept runs substantially cooler than the area that is being swept by the pad, which causes a temperature gradient across the disc. You want the disc to be evenly heated throughout. Having one portion running cooler than the other leads to distortion and premature cracking.
Makes sense for iron, and is a critical selection criterion for your pads on iron rotors (make sure the radial depth matches the disc well).
But is this true for PCCB? Considering that PCCB discs don't suffer measurable loss of thickness through their usable lifetime, it seems apparent that they "work" substantially differently than iron discs do. An FAQ on the ST website says carbon ceramic has 3x the heat conductivity of iron. So maybe this would help enough with the gradient problem?
While the unsprung weight savings of carbon ceramic discs is nice, we don't believe all of the negatives of the material are worth that weight savings if you're tracking your car.
They almost certainly are not. While I probably dispute some of your claims, in general one must agree that PCCB material has challenges. Even if they were equivalent to iron otherwise, the operating cost is very high and few drivers will actually be able to realize any value from that. Of course, as enthusiasts we dump lots and lots of money into ridiculous race parts anyway.
But anyway my question was specifically targeted towards your claim of incompatibility with ST (or OEM for that matter) discs. I think it's unfair to make it a foregone conclusion that if you want the subjectively best caliper you must also go with not-the-best rotors.
AP did offer CCM rotors (w/ST discs) for GTR sold through Stillen, and in fact RB handled quite a few of their after service; Including refurbishing ST discs, supplying upgraded 6/4 pot calipers direct replacement to OE Brembo calipers (one order in house being built), and sintered pads for their CCM rotors under OE calipers.
These 400mm disc assemblies are larger than the standard OE iron discs
...
And now - STILLEN and AP Racing have optimized a specific set for your R35 GT-R and its factory brake calipers
That kit specifically uses the factory calipers. Apparently the OEM rotor size is 388mm F/380mm R. So in the rear, it would seem they have designed for 20mm of the ST rotor to be unswept. Of course, they could have designed (or selected an existing) rotor disc with a larger ID. I could only find one blurry picture of the brakes installed, and there does appear to be a very healthy gap from pad to inner diameter.
Thanks Jeff. Inline:
I see. So the min. thickness of the adapter and mounting height of the radical caliper requires a minimum disc diameter. The ST discs (per AQ website anyway) are available in both iron and PCCB fitment, and the iron won't work. Presumably the PCCB sized discs are larger. Do you know if they are large enough for the AP caliper to fit?
That is correct on the minimum required diameter. The front OEM PCCB discs are 410mm diameter. The front discs in our system are 394mm diameter. The other problem however is the disc pathway on the calipers. Any given caliper is able to fit discs of a certain diameter range. If the disc is too large in diameter, the arc of the disc will interfere with the caliper body (circled areas in the diagram below). The top drawing is a disc that is too large for a given caliper. The bottom is a disc that fits properly in a caliper. As you stretch a caliper across a larger disc, you have to worry about proper pad orientation on the disc as well.
Makes sense for iron, and is a critical selection criterion for your pads on iron rotors (make sure the radial depth matches the disc well). But is this true for PCCB? Considering that PCCB discs don't suffer measurable loss of thickness through their usable lifetime, it seems apparent that they "work" substantially differently than iron discs do. An FAQ on the ST website says carbon ceramic has 3x the heat conductivity of iron. So maybe this would help enough with the gradient problem?
That's a good question. Heat flows through iron discs in all directions (across the face, down into the center, vanes, etc.), not a uniform direction. On the carbon ceramic discs, heat will readily flow along the strands, but not as readily down into the other layers of the discs. The heat from the pads sits on the surface. That's why the large radial depth is needed to spread that heat across a larger surface area so it can radiate. If you concentrate all of the heat from a shorter radial depth pad on a smaller section of the disc face, you're eliminating the disc's primary mechanism to shed heat. The carbon disc won't crack, but those pads and the disc are going to run extremely hot in the swept area.
They almost certainly are not. While I probably dispute some of your claims, in general one must agree that PCCB material has challenges. Even if they were equivalent to iron otherwise, the operating cost is very high and few drivers will actually be able to realize any value from that. Of course, as enthusiasts we dump lots and lots of money into ridiculous race parts anyway.
But anyway my question was specifically targeted towards your claim of incompatibility with ST (or OEM for that matter) discs. I think it's unfair to make it a foregone conclusion that if you want the subjectively best caliper you must also go with not-the-best rotors.
We weren't trying to make it a foregone conclusion that our AP Racing calipers wouldn't fit any other discs, including the ST discs. Nor were we trying to be closed-minded. We always listen to our customers. It's one of the reasons why it took so long for us to develop our 991 GT3 brake kit in the first place. There are numerous technical challenges involved, and my comments here and elsewhere are made with all of those challenges in mind.
As a general rule, the discs and calipers from one manufacturer are not interchangeable with those from another manufacturer. There are too many variables involved. Radial depths, disc pathways, disc PCD, caliper mounting bolt spacing, PL Dimension, type of disc mounting hardware used...there is a laundry list of factors that typically prevent everything from coming together like Legos. Many times a custom solution can be created, but we have to keep the goal of that custom solution in mind. In this case, we believe we are matching the best discs to the best calipers. The iron AP Racing discs flow a lot of air and run cool, are extremely lightweight for iron, last a long time, and are a reasonable amount of money to replace. They are a fantastic blend of those qualities. That statement is based on experience servicing many thousands of customers across all levels of motorsport, from NASCAR Cup to IMSA, to club racers and HPDE enthusiasts. If you look at owner reviews of our products, that's what you see over, and over, and over again.
AP did offer CCM rotors (w/ST discs) for GTR sold through Stillen, and in fact RB handled quite a few of their after service; Including refurbishing ST discs, supplying upgraded 6/4 pot calipers direct replacement to OE Brembo calipers (one order in house being built), and sintered pads for their CCM rotors under OE calipers.
That kit specifically uses the factory calipers. Apparently the OEM rotor size is 388mm F/380mm R. So in the rear, it would seem they have designed for 20mm of the ST rotor to be unswept. Of course, they could have designed (or selected an existing) rotor disc with a larger ID. I could only find one blurry picture of the brakes installed, and there does appear to be a very healthy gap from pad to inner diameter.
Very anxious to hear from Essex!
You'll note that the CCM discs for the GTR were not sold through Essex, they were sold through Stillen. Stillen is AP Racing's North American Distributor for road car parts. Essex is AP's North American Distributor for competition parts (track use). AP Racing considers the CCM discs a road solution for all of the reasons I've noted in prior posts.
We aren't foolish enough to believe that iron discs will rule supreme for track use forever. Alternative materials are certainly the way of the future. That said, whether or not carbon ceramic is that material remains to be seen. Our experience and data suggest that the current iterations of carbon ceramic are not as good as iron on many levels for how our customers are using them on their track cars. They have too many issues and compromises, and they're too expensive (even considering irrational decisions by rabid enthusiasts ). When we have a carbon ceramic material that we believe will meet our customers' expectations for heavy track use, we will certainly share it with the masses!
On a personal note, I have experience with Surface Transforms discs, probably long before just about everyone else on this forum. Almost eleven years ago, when I worked at StopTech in 2007, Surface Transforms was courting StopTech as their North American distributor for their continuous fiber discs. We put them through various testing cycles and we were excited about how promising they looked. Things went a bit wobbly when I installed them on my 2003 Z06 Corvette however. They worked fairly well on the street, but I destroyed them in a single afternoon at Buttonwillow. The discs had a whole bunch of surface eruptions and oxidation on their faces, while our iron system held up fine under the same exact conditions. At that point we put a halt on their release to the public, and I asked our engineering department to request further development. I wasn't prepared to put my name behind a $15,000 product that didn't meet our customer's expectations (that's what we planned to charge for the whole brake system at the time). While that was a long time ago, I personally still have seen any concrete evidence that carbon ceramic discs can outperform iron discs for track use in terms of fade resistance, running temps, wear rates, longevity, ease of service, replacement cost, etc. Iron discs still offer a superior blend of these features.
we believe we are matching the best discs to the best calipers.
best iron discs, yes. best discs period ... there are variables.
yes, CC isn't the perfect material and damn it's expensive. your experience with oxidation surely isn't shared by most. Ferrari Challenge comes to mind as an example. none of my circle of friends nor myself have had problems with oxidation due to tracking.
i just hate to give up the weight if there's a way to get around that. something just came to me: what are the 19" wheel fitment options for GT4 w/ PCCB? The info is scattered all around. It seems maybe the GA1R will fit but you will get scoring on the barrel, ie not actually enough clearance even if it "works". i'm thinking that the extra clearance from the AP calipers (vs OEM PCCB) makes 19" wheels more palatable.
anyone know what the total weight (wheel+tire) is for factory 20 vs forgeline 19? probably not 6# savings per corner.
best iron discs, yes. best discs period ... there are variables.
yes, CC isn't the perfect material and damn it's expensive. your experience with oxidation surely isn't shared by most. Ferrari Challenge comes to mind as an example. none of my circle of friends nor myself have had problems with oxidation due to tracking.
I agree, and I tend not to talk in superlatives. As noted, we believe our discs are the best blend of all of the factors I mentioned...wear, weight, heat reduction, longevity, fade resistance, replacement cost, timely replacement, etc. That assessment is based on our aftermarket/club racer customer needs and wants. It is a far different picture in pro racing. For the NASCAR Cup teams we support, they want the disc to cross the finish line without fade, win the race, and then it can fall to pieces. For that reason we have a range of calipers and discs for those customers depending on which track they are running, etc. The goals are much different by usage environment and customer.
In terms of oxidation, we have seen lots of problems on that front. I just set several Lamborghini Huracan Performante customers up with discs because they thrashed their carbon ceramic ones in very short order at COTA. If you go check out the C7 Z06 forum, there are many discussions on that topic as well. From what we've seen, the typical C7 Z06 customer on sticky tires can get as few as 10 days out of their discs before they are trash. Keep in mind that oxidation includes burning up on the inside, and passing below the disc's safe minimum weight, not just surface eruptions. We've also seen it among Audi RS3/TT-RS/R8 customers, BMW, and other exotics. For example, we supply Exotics Racing (and other schools and driving experiences) with iron brake discs for their entire fleet. They immediately swap out the carbon ceramic discs because they aren't sustainable from a maintenance and cost standpoint. We have firsthand experience on a lot of different platforms. I think the problem may be more widespread than everyone may realize. The fact that all of the auto manufacturers tout carbon ceramic as the ultimate 'race-inspired' solution for track use certainly doesn't make it any easier on the consumer.
i just hate to give up the weight if there's a way to get around that. something just came to me: what are the 19" wheel fitment options for GT4 w/ PCCB? The info is scattered all around. It seems maybe the GA1R will fit but you will get scoring on the barrel, ie not actually enough clearance even if it "works". i'm thinking that the extra clearance from the AP calipers (vs OEM PCCB) makes 19" wheels more palatable.
anyone know what the total weight (wheel+tire) is for factory 20 vs forgeline 19? probably not 6# savings per corner.
will the AP kit clear any 18" wheels?
i know, i'm getting off into the weeds here ..
No worries! As enthusiasts, we completely understand. As a lightweight car junkie myself (I own or have owned numerous Miata, MR2 Spyder, S2000, Integra Type R, etc.), we totally get the quest for gram reduction / adding lightness. We strive to do that as much as possible. If you look at our brackets, hats, etc., our engineers remove as much mass as possible while designing towards our endurance goals as described above. We understand. Our iron system shaves about 33 unsprung lbs. off of the OEM iron GT4 system, which we think is a fairly solid accomplishment.
We have wheel fitment templates for all of the brake kits we produce (see image below). They are available on all of the kit pages on our website. Here are the ones for the GT4:
Confirmed wheels that fit on the front without a spacer:
OEM front 20x8.5"
Forgeline GE1R, GS1R, and GA1R in 19x9 +52
We haven't had any issues with rear fitment at all.
The president of Forgeline runs our brake kit on his personal car, and their team is familiar with our fitments. They would be happy to help ensure fitment around our kit templates.
Our 394mm/380mm kit for the GT4 will not fit 18" wheels. Ideally we would have been able to produce a kit to fit 18's, and we have a 372mm disc in our arsenal that we designed explicitly for 18" applications. For example, on the 997 kit that we just released this week, we use a 372mm/365mm disc setup that is plenty large enough to handle the heat but will fit inside 18's. Going back to our earlier fitment conversation...we couldn't use the smaller discs on the GT4 because we need to push the disc out to make room for the caliper bracket. From a heat capacity standpoint, our 372x34mm 84 vane front would have been ample on the front of these cars, and it's a couple pounds lighter than the 394mm (we have 1000 HP Z06 tracking our 372mm without fade or issue). Same goes for the rear. Frankly, our 355x32mm could get it done on the front of a GT4. Unfortunately those discs don't fit into the overall packaging picture.
I empathize with your frustration. From a supplier and fellow enthusiast perspective, it frustrates us as well! We are always looking for lighter and faster, and our kits tend to be exactly that vs. everything else on the market.
Below you can see just a few of the cars we've equipped with iron discs that came with carbon ceramics. There is no perfect, but we are doing our darnedest to make disc kits and complete brake kits that solve our customers needs and make them go faster, increase confidence, reduce costs, etc. Again, we have many, many, thousands of miles of real-world experience with our setups. The school cars are on track all day, every day, and we have data on how many miles they get/got out of discs, pads, fluid, how much downtime, etc. The cost per mile of carbon ceramic vs. iron isn't even remotely close.
In terms of oxidation, we have seen lots of problems on that front. I just set several Lamborghini Huracan Performante customers up with discs because they thrashed their carbon ceramic ones in very short order at COTA. If you go check out the C7 Z06 forum, there are many discussions on that topic as well. From what we've seen, the typical C7 Z06 customer on sticky tires can get as few as 10 days out of their discs before they are trash.
10 days? That's grandma driving! I would be extremely happy with 10 track days of usage.
No worries! As enthusiasts, we completely understand. As a lightweight car junkie myself (I own or have owned numerous Miata, MR2 Spyder, S2000, Integra Type R, etc.), we totally get the quest for gram reduction / adding lightness. We strive to do that as much as possible. If you look at our brackets, hats, etc., our engineers remove as much mass as possible while designing towards our endurance goals as described above. We understand. Our iron system shaves about 33 unsprung lbs. off of the OEM iron GT4 system, which we think is a fairly solid accomplishment.
yeah, and additional clearance. It's stellar, and well priced IMHO.
i come from open wheel, and lotus, so as a track weapon the gt4 is heavy in my book.
i found my previous question and answer about the wheels here:
Originally Posted by BGB Motorsports
Depends on which model, and size configuration. For reference, the GS1R in 19x9 and 19x10.5 will run ~19lbs front, and ~20lbs rear. Stock wheel weight numbers I found online are 23.24lbs front, and 25.86lbs rear. Overall, you are looking at approx. 4-5lbs per corner weight savings!
which i think puts me over the edge on "sucking up" the disc weight gain vs PCCB. honestly, i think the ST rotors might work, but i don't want to be the one to do the testing only to find out that you were right.
10 days? That's grandma driving! I would be extremely happy with 10 track days of usage.
yeah, and additional clearance. It's stellar, and well priced IMHO.
i come from open wheel, and lotus, so as a track weapon the gt4 is heavy in my book.
i found my previous question and answer about the wheels here:
which i think puts me over the edge on "sucking up" the disc weight gain vs PCCB. honestly, i think the ST rotors might work, but i don't want to be the one to do the testing only to find out that you were right.
10 Days...Lol...I like it. I have a C6 vette track car and it feels like a barge compared to my roadsters. My current obsession is the Lotus 7 (and all of its derivatives)...seriously thinking about getting into one, but my tinkering time is incredibly slim right now unfortunately.
Thank you very much for the comments, good questions, and thoughtful discussion!
07-09-2018, 02:08 PM
). When we have a carbon ceramic material that we believe will meet our customers' expectations for heavy track use, we will certainly share it with the masses!
I would be extremely happy with 10 track days of usage.
