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Unread 08-03-2010, 09:02 AM   #1
Steve Geiger
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Default Ceramic Brakes, NY Times

Superbrakes for Civilians? The Cost Is the Obstacle
Published: July 30, 2010

FOR more than 30 years, Formula One racecars have benefited from powerful brakes that vastly outperform the systems available on any showroom model. The gap may be narrowing, though: high-tech materials similar to those on the racetrack began showing up in exotic sports cars about 10 years ago, and some luxury models now offer them as well.

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SPEED DIET Carbon-ceramic rotors of ZR1 Corvette save 11 pounds over iron.
How about the rest of us? Even underpowered grocery-getters would gain safety and weight advantages with advanced brakes — but they probably won’t get them anytime soon.

The special composite materials employed at the leading edge of brake technology withstand heat better than the iron components commonly used in road vehicles — and at the same time weigh less. Both factors are important. Brakes slow the car by using friction to convert kinetic energy into heat; the downside is that the heat generated can also lead to a loss of braking power. Reducing weight, of course, pays off in improved fuel economy.

Superbrakes come in two varieties, and the rotor — the disc of disc brakes, which is squeezed by the brake pads to slow the car — is the key part of each.

Carbon-carbon rotors, a composite of carbon fiber and carbon, made the first great leap in stopping performance. Used mainly on racecars, where they first appeared in the 1970s, they are not well suited to road use because of rapid wear and the need to operate at high temperatures. And they are expensive.

Carbon-ceramic rotors, a composite of carbon fiber and silicon carbide, could be the superbrakes for the rest of us. They first hit the road — or more accurately, the railroad tracks — in the 1980s, when British engineers developed them for high-speed trains.

In 2001, the Porsche 911 Turbo introduced carbon-ceramic brakes to road-going automobiles. Now, they are available on the Chevrolet Corvette and on top models from brands including Aston Martin, Audi, Bentley, Bugatti, Ferrari, Lamborghini and Mercedes-Benz.

Carbon-ceramic brakes would even be a boon for owners of econoboxes driven in the suburbs. For one thing, brake rotor replacement will probably become a thing of the past, as the carbon-ceramic rotors, which are extremely hard and wear minimally, might well outlast the car. Tadge Juechter, chief engineer for the Corvette, said that carbon-ceramic rotors “last basically forever in street use.”

And with carbon-ceramic rotors and the special pads that are used with them, that nasty black grime that coats wheels would be only a bad memory.

But most important, vehicle weight would be reduced significantly, because a carbon-ceramic rotor weighs about 40 to 50 percent less than a cast-iron rotor. A Chevrolet spokesman, Dave Caldwell, said that the carbon-ceramic rotors used on the Corvette ZR1 were each 11 pounds lighter than the corresponding metal rotors of other Corvette models.

The weight savings are greater than the numbers might suggest because the brake rotor, attached near the extreme end of the suspension, is what engineers call unsprung weight. In cornering, the weight of the rotor adds inertia to the suspension’s movement, making it difficult for the spring and the shock absorber to maintain control. Less weight acting on the suspension means the tire is more likely to stay in touch with the road.

In addition, the overall weight savings possible with carbon-ceramic brake rotors exceed that achieved by the rotor swap alone.

Mr. Juechter says that because a carbon-ceramic rotor is lighter than an iron part, the heft of the suspension that controls it, and of the body structure to which the suspension is attached, can be reduced. So the overall vehicle weight savings could be considerable.

So why aren’t automakers putting carbon-ceramic brakes on every vehicle? In a word, cost.

While the carbon-carbon brakes used on Formula One cars are hideously expensive, carbon-ceramic brakes are merely outrageously expensive: an $8,000 option on selected Porsche models and $12,500 on the Mercedes-Benz SLS AMG.

Although the silicon carbide and carbon fiber used to make the rotors are not that expensive, the manufacturing process is costly. Once the materials have been combined and shaped, the rotors have to be baked at very high temperature for several days in special ovens. Production is limited by oven capacity and by the time it takes to cook them.

Brembo SGL Carbon Ceramic Brakes of Milan produces many of the carbon ceramic rotors used on production vehicles. Roberto Vavassori, business development director, said in an e-mail interview that the company hoped to whittle down the cost.

Mr. Vavassori said that while Brembo was actively working to improve the five-day manufacturing process, he did not see carbon ceramic brakes coming into wide use for another decade.
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Unread 05-31-2013, 06:04 PM   #2
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