The Problem with 19" Wheels and 410mm Porsche Ceramic Brakes

When APEX first set out to create 19” wheels for Porsche applications, one of our primary goals was to clear the optional 410mm Porsche Ceramic Composite Brakes (PCCB) package. As a wheel manufacturer hyperfocused on offering strong, lightweight, and affordable solutions for track enthusiasts and club racers, we perform exhaustive research prior to entering into a new market in an effort to uncover the needs and pain points of its enthusiast community. In addition to reviewing things like suspension designs, tire availability, club racing rules, and regulations, etc., there is a strong emphasis on studying both factory and popular aftermarket brake specifications. This article outlines our research on the ceramic brake system in relation to engineering our 19” SM-10 Porsche wheels.

What We Found in our Research of This Application

As our engineers took on this challenge, we discovered clearance issues early on that greatly concerned us. Although technically a 19” wheel can clear the PCCB system, we believe that it should be avoided.

What did our research find? The tolerance between a 19” wheel with an optimized barrel design and the front caliper of the PCCB kit is dangerously tight, and it’s resulting in serious issues for many owners who’ve fitted 19” wheels. When we say it’s tight, we mean a gap that is less than 2mm. It could be as small as 1mm.

In the garage, 19” wheels can technically clear, but it is important to note that wheels will flex under load. At that minuscule tolerance, even if the calipers do not directly make contact with the barrel of the wheel, debris will inevitably get lodged in between. We’ve seen rocks and other types of debris cause deep scoring of the barrels (which are only a few millimeters thick). Damaging the wheel barrel compromises its strength and is unsafe, especially when a car is frequently driven at speed on the race track.

The APEX Research Process

Our quest to clear the PCCB option started with 3D laser scanning and real-world testing on two GT4 volunteer cars. One was equipped with 380mm steel brakes, and the other was fitted with the optional 410mm ceramic brakes. Scaling up our existing 18” SM-10 design allowed us to clear the 380mm steel brakes with ease, but the ceramic brakes required more barrel clearance.

An APEX engineer with extensive experience in custom forged wheel design recognized a zero degree draft on the barrel would be required to clear. This means the barrel is as wide as possible front to rear on the inner barrel’s diameter, with no taper at all. Most wheels typically have some taper to them. A zero degree draft is the maximum amount of space any wheel can have. Go beyond, and a tire won’t slip over the barrel.

Even with this ultra-flat barrel profile designed into the wheel, the tolerance is so tight between the caliper and barrel that it did not meet our internal safety standards. With other aftermarket wheels being sold for this application, we expected to find more clearance using this design element.

Our findings prompted us to further investigate the wheel offerings from other manufacturers who actively sell 19” fitments to owners of PCCB-equipped Porsches. We even conducted 3D laser scanning on their wheels to see if there was something we were missing. We discovered very similar tolerances with their products, and when we spoke to customers running these wheels, it was made clear that the damage was being tolerated in the name of performance and tire availability. Unfortunately, in many cases, this damage often led to costly repairs to the caliper(s) and the replacement of the wheel(s).

Pictured: Brand X Forged Motorsport Wheels with 410mm PCCB

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Porsche Cayman with APEX 19" SM-10 wheels in Anthracite

The damage seen in the images above occurred on a PCCB equipped GT4 with a new set of custom forged wheels designed for motorsport use. The damage occurred almost immediately after installing the new wheels onto the vehicle, with very few street miles logged before the driver discovered evidence of direct contact between the calipers and wheel barrels. This car was being prepared for the track, so imagine how much more contact there could have been under hard cornering load and with lots of debris present.

Throughout this research it became increasingly clear why Porsche elected to install 20” wheels on models like the GT4 and 991 GT3, and why their Motorsport counterparts (GT4 Clubsport & GT3 Cup) required a smaller diameter brake package with revised suspension geometry to accommodate an 18” wheel and tire package.

Our Recommendations

From a performance and tire cost/availability perspective, we very much wanted to be able to confidently offer 19” wheels to track enthusiasts with 410mm ceramic brakes. However, at this point, we have gathered enough information to conclude that recommending 19” wheels for these applications would not be appropriate; it would not lead to the type of customer experience for which APEX is known. As a result, we did not pursue a zero draft barrel design to ensure our wheels could not be used for this application.

What’s our advice for those who have PCCB’s but want to track a lot?

Shelve them in your garage while the calipers are still pretty and the rotors still have plenty of life, and mount up an aftermarket kit like the AP Racing by Essex Radi-CAL BBK. Their 6 piston 394mm brakes (pn 13.01.10083) clear our 19” wheels and other properly designed 19” motorsport wheels. For those of you who would like to run 18″ wheels like the GT4 Clubsport, PFC offers a 6 piston 380mm BBK (pn 0380.001/2 sport & 0380.0001/2 race). When it’s time to sell the car, you can reinstall the PCCB for your prospective buyers. The ceramic kit is impressively light, but even if your wallet can absorb the cost of entry and the drastically higher running costs over steel rotors, you’re ultimately stuck with heavier 20” wheels and the limited, expensive tires required.

For enthusiasts enjoying their PCCB equipped Porsche predominantly on the street with no intentions of removing the brakes, APEX will soon have a variety of 20” fitments available in both five lug and center lock applications. Visit our home page to sign up for our newsletter to be notified of these product releases.

What About Other Porsche Ceramic Brake Applications?

APEX 18” and 19” Porsche wheels clear all other Porsche Ceramic brake applications to date, with front rotor specs ranging from 350mm to 380mm from various generations of 911 and Cayman/Boxster chassis.