Designer Braking

High-tech ceramic brakes are ready - but oh, what a price General Motors Corp. and Ford Motor Co. have produced good headlines with their recent attempts at technical one-up-manship, but German automakers Mercedes-Benz (DaimlerChrysler AG's luxury car unit) and Porsche AG are locked in a little, non-public tussle of their own: which can claim bragging rights as the first to offer new, high-tech braking systems sporting ceramic-composite rotors.

In its press material, Mercedes flatly says it is the world's first automaker to offer ceramic brake discs for a production vehicle, with their introduction as standard equipment for the CL 55 AMG "F1 Limited Edition," of which only 55 units will be produced.

Mercedes says orders for the CL 55 AMG, a version of the CL coupe modified by Mercedes' in-house performance "tuner" AMG, are being taken now for vehicle delivery in the fall. Apparently by Mercedes' reckoning, that timeframe beats Porsche AG and its launch of a similar ceramic-disc braking system for this fall's 911 Turbo.

Mercedes says the carbon-fiber reinforced ceramic brake discs will be fitted only on the front wheels. Like Porsche, it claims greatly enhanced performance, reduced unsprung mass and drastically extended service life for the new ceramic rotors.

And like Porsche, Mercedes plans to charge accordingly for the cache of "designer" braking: Following the system's introduction as standard equipment for the CL 55 AMG F1 Limited Edition, the so-called "C-Brake" rotors will be offered as an option early next year for the S 55 and CL 55 AMG models at a cost of $5,650.

Porsche, which goes Mercedes one better by fitting its new Porsche Ceramic Composite Brake (PCCB) at all four corners of the new 911 Turbo, will tune up its customers for at least $10,000 for the option, although the final price apparently isn't yet settled.

Mercedes claims its new ceramic-composite rotors can withstand a maximum temperature load of 2,550øF (1,400øC) and exhibit low levels of thermal expansion, reducing brake "judder" (jar and shudder) and squeal under hard use. The discs are said to be good for 186,000 miles (300,000 km) of use - and they do not corrode.

Each C-Brake rotor weighs 13.2 lbs. (6 kg) less than a conventional cast iron rotor, which reduces unsprung mass and also translates to positive effects on vehicle steering and dynamics, says Mercedes. Early information does not provide data regarding reduction of braking distances, however. The eight-piston calipers, supplied by Italian brake specialist Brembo, were specifically designed for the characteristics of the ceramic discs.

Mercedes also says it has patented its production process for the fiber-reinforced ceramic discs.

Porsche's PCCB system can be spotted by its distinctive yellow-colored calipers. The PCCB design incorporates a ceramic-composite brake rotor that's made in a three-step process. Carbon fibers are coated with a silicate in a high-vacuum process at 3,100øF (1,700øC). Superficially, apart from the unique coloration of the calipers, PCCB discs appear virtually the same as conventional cast-iron disks.

The discs are even crossed-drilled and vented from the inside like cast-iron disks, to create the illusion of sameness. But the PCCB system weighs half that of conventional discs. This saves up to 11 lbs. (5 kg), depending on disc size. Porsche says PCCB negates half the weight increase of the 2001 911 Turbo compared to its predecessor.

Besides contributing to fuel economy, the reduction in unsprung mass will improve suspension response and behavior, Porsche promises.

Porsche Chairman Wendelin Wiedeking predicts the PCCB should last virtually for the life of the 911 Turbo - at least 100,000 miles (162,000 km). The ceramic brake enjoys extended life because it is virtually immune to corrosion. Salt sprayed on roads, for example, does not corrode the new discs.

In addition, the PCCB discs are coupled with all-new metallic pads that develop extremely high and very constant friction during deceleration; brake temperature becomes a minor factor because the PCCB provides fade-free braking almost regardless of how hot the rotors become. Wet-braking capability also is improved because the new brake linings do not absorb water as conventional linings do.

Porsche expects to build 2,000 911 Turbo units annually. All of these can accommodate PCCB, and older models also can be retrofitted with the PCCB system.