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The brake discs are made from reinforced ceramic, a material which has already proven itself many times over in the field of aeronautical and aerospace engineering. The ceramic material''s composite structure is made up firstly of silicon carbide, an extremely hard and abrasion-resistant base material with a crystal structure similar to that of diamond. The high-strength carbon fibres which are then embedded in this base material are able to absorb the stresses that occur in it.
The high-tech material offers a whole spectrum of benefits. The most visually apparent of these is its insusceptibility to corrosion; no signs of rust formation will be found on a ceramic brake disc. The sporty looks, featuring distinctive perforation patterns and red brake callipers, also add eye-catching styling touches.
The technical benefits have an even greater impact: first, there is the weight-saving of some five kilograms, or around 50 percent, per wheel. The result is a clear reduction in the unsprung masses at the wheels, which in turn makes the ride even more comfortable. The vehicle''s handling characteristics are also enhanced by the brake unit''s lower weight.
The high abrasion resistance of the ceramic discs means a service life of up to 300,000 kilometres under standard day-to-day operating conditions, four times greater than that expected of a steel disc. Plus, the degree of wear over the brake''s service life is a mere 0.5 millimetres.
The ceramic braking system also represents a significant step forwards in terms of brake performance. The discs are able to offer tremendous braking power, even when the vehicle is being driven to its handling limits. Resistance to fading, which refers to the marked loss of braking power following repeated application of the brakes as can occur on long mountain descents, is far superior than with conventional brakes. For high-performance vehicles such as the W12-powered A8 this translates into far greater safety reserves out on the road.
Motorists are also able to appreciate the virtues of the ceramic brake on a more subjective level, thanks to the clearly defined pedal feel under all operating conditions. Neither is there any risk of the state-of-the-art brake discs being afflicted by brake judder, irrespective of the operating conditions.
Ceramic discs with a diameter of 380 millimetres are fitted at the front to partner 19-inch wheels. The discs at the rear measure 356 millimetres across. The ceramic brake disc ring is bolted by means of ten flexible connector elements to a stainless-steel bowl which in turn links it to the wheel hub. The elaborate cooling duct geometry used for the internally ventilated brake disc ensures optimum brake disc cooling. 6-piston monoblock aluminium callipers from Brembo at the front brakes and sliding-calliper brakes at the rear guarantee a vice-like grip on the discs. Electromechanical operation of the parking brake continues to make up part of standard specification as it does on all the other A8 models.
The new ceramic brake will be available to order as an option for the A8 W12 and A8 L W12 quattro 12-cylinder models from July2005.