Braking System of the Subaru ImprezA WRX STI
Know-how developed in racing helps Brembo engineers to propose innovative solutions for original equipment automotive braking systems that provide high levels of performance, safety, and comfort. As the flagship Subaru performance model, the STI requires such a system. The Brembo system for the Subaru WRX STI includes calipers, rotors, and pads.
The front caliper for the STI is a four-piston, two-piece aluminum design with differentially sized pistons (46 mm and 40 mm) to equalize piston pressures and minimize uneven pad wear. The rear caliper is a two-piston, two-piece aluminum version with slightly larger pistons (40 mm) than the 2004-2007 editions.
The two-piece aluminum body offers weight savings as well as increased stiffness to reduce fluid displacement and caliper deformation, which leads to a firmer and more consistent feel of the brake pedal. The caliper body has been designed to be as light as possible while meeting stiffness criteria. Both front and rear calipers have internal fluid passages to prevent damage to external fluid lines.
During development, caliper mechanical resistance and deformation are verified analytically with the use of advanced Finite Elements Analysis (FEA). In addition, physical tests are carried out with Brembo R&D laboratories and on the vehicle at the international road-racing circuits.
Brembo brake disc venting designs include its patented pillar-venting technology, shown on the top disc.
Both the front and rear cast iron rotors utilize Brembo-patented pillar-vented technology to improve cooling and crack resistance of the braking surface. The front discs are 12.8 inches x 1.18 inches (326 mm x 30 mm) while the rears are 12.4 inches x 0.8 inches (316 mm x 20 mm). Disc size and shape have been optimized to assure the best behavior under high thermal loads, both for mechanical resistance and for deformation during braking. Front and rear discs are made with a high-carbon cast iron to obtain excellent performances and, at the same time, improve noise/vibration/harshness (NVH) behavior.
The pads for the STI are a high-performance, non-asbestos organic friction material that offers a wide heat range for everyday and performance driving. Pad size and shape have been optimized to improve longevity and improved fade resistance.