Hard up for details on Porsche’s new Surface Coated Brakes, or PSCB for short? We visited with the company’s braking and chassis engineers in Germany for more information, and we can say this much: They’re more than just a new way for Porsche to empty your pockets of a few thousand bucks. Besides the brakes’ size and gleaming white-painted calipers, they feature iron rotors coated in a thin, ultra-hard layer of tungsten carbide. This gives them an edge in performance along with reduced wear and dust production over the 2019 Cayenne SUV’s standard-fitment iron rotors. Here’s how they work:
From Dust to (Less) Dust
Porsche’s pathological commitment to outbraking the competition with shorter stopping distances and minimal fade makes for a few minor annoyances, such as: Some Porsches’ brakes occasionally squeal and can give off lots of dust. While many Porsche customers gladly accept the trade-offs for maximum braking performance, some have been pining for the stopping power expected of a performance car with less noise and dust.
Porsche looked at using low-noise, low-dust brake pads as every other manufacturer does. Testing revealed these “comfort pads,” as Porsche calls them, to be unsatisfactory. (Just look at how they doomed a Nissan 370Z we lapped at our annual Lightning Lap track test a few years ago.) So, working with Bosch, Porsche homed in on the rotor instead.
Porsche found that discs are responsible for the majority of brake dust and that pads, commonly thought to be the biggest contributor to dust, only account for 30 percent. The reason is that while pads and rotors both lose thickness over their life cycles, rotors have far greater surface area than pads. All that material has to go somewhere, and on Porsches, that schmutz—scientifically speaking, it’s ferric oxide—ends up dirtying pretty wheels.
To reduce brake dust, Porsche reduces the amount of material worn off the rotor during its useful life. Tungsten carbide is handy for this, being several magnitudes harder than steel on the Vickers scale. Only a fraction of the material is needed relative to iron to provide similar longevity without adding excessive weight. Each PSCB rotor features an iron core wearing a 100-micron-thick (0.1 millimeter) coating of tungsten carbide. Once that layer has worn away—Porsche says it lasts up to 30 percent longer than its iron rotors—the disc is deemed in need of replacement. Porsche, comparing that 0.1 millimeter of effective allowable wear to the 1 millimeter allowable on a hypothetical iron rotor, claims PSCBs reduce brake dust by 90 percent.
One hitch is that these new PSCB rotors are incompatible with traditional ceramic and semi-metallic brake pads, so Akebono provides pads made of a never-before-seen compound. It will remain unseen, because all parties involved are shrouding those pads in secrecy. We do know that the pads are incompatible with regular iron rotors, meaning you can’t double dip on rotor wear and dig into the iron disc after you use up the coating of tungsten carbide. We’re told that dealers will measure the brakes’ wear and determine their replacement. If you were to skip a dealer visit around brake-change time, you’d notice a distinct reduction in braking performance as the last of the coating wears away.
In prime form, however, the PSCB rotors and those special pads combine for a higher friction coefficient than Porsche’s standard iron rotors and boast the same resistance to fade during repeated use. Porsche says that Cayennes so equipped are expected to stop a few feet shorter from highway speeds than their iron-rotor counterparts, a feat partly attributable to the PSCB rotors’ size. Measuring 16.4 inches in diameter up front and 14.4 inches in back, they’re well beyond the base Cayenne’s 13.8-inch front and 13.0-inch rear discs (and the S model’s upsized 15.4-inch front rotors), although well short of the optional carbon-ceramic rotors’ 17.3- and 16.1-inch diameters.
Isn’t It Iron-ic?
In the surreal context of Porsche option pricing, the PSCB package is a relative deal when added to the Cayenne and Cayenne S for a paltry $3490. That same sum would buy you 18 sets of wheel caps with full-color Porsche crests on them. Spring for the $125,650 2019 Cayenne Turbo, and Porsche will include the special brakes gratis. Remember, the Cayenne’s other available brake package, the track-focused carbon-ceramic option, costs $9080. Here you get the same massive 10-piston front calipers and four-piston rears that squeeze those ceramic rotors, only they’re painted a brilliant white instead of yellow so you can easily gauge how little dust the brakes produce. Oh, and after about 200 to 300 miles of driving from new, the PSCB discs’ manufacturing filth is polished away, revealing a striking mirror shine. Get ready to see them glinting not only on the Cayenne but on other Porsches, too, as the company is working to expand availability to more models.
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