Proactive Chassis Control
The MP4-12C's clever suspension bits worked so well in Sebastien Loeb's Citroen rally car that the FIA banned this technology in 2006. What looks like an ordinary shock absorber at each wheel is instead a hydraulic cylinder. In relation to wheel motion, a piston inside each cylinder pumps hydraulic fluid into and out of the chambers above and below the piston. All eight chambers are connected to two accumulators, each of which contains fluid and nitrogen separated by a bladder.
Unlike conventional shock absorbers, these pistons have no orifices or valves. Instead, the flow restrictors are located where the hydraulic lines attach to each cylinder. The size of the restriction, which is varied by an electronic controller, determines the amount of damping provided.
The pressurized nitrogen contained within the two accumulators acts as a spring to resist roll motion; each accumulator handles one cornering direction. Individual wheel motion is resisted by the coil springs.
This technology saves the weight and complexity of conventional anti-roll bars, but more significantly, it's a boon to tuning. Soft springs and gentle damping provide a pleasant ride. A high accumulator spring rate assures minimal body roll, which is further diminished by adding more fluid to each accumulator. When the driver turns a cockpit knob from the normal setting to sport or track mode, an electric pump adds the appropriate amount of hydraulic fluid. (Infiniti and Toyota also use versions of this Tenneco Kinetic system.)
Key MP4-12C suspension components (control arms in front, multiiink in back) are forged aluminum. There's an Eibach coil spring at each corner. Pirelli P Zero and P ZeroCorsa tires are available, and the MP4-12C offers two brake systems. The standard stoppers supplied by AP Racing (a Brembo subsidiary) use two-piece iron and forged aluminum rotors. Those with track-day aspirations will be better served by the optional Brembo carbon-ceramic system.
□ BELOW: HYDRAULIC LIMES CONNECT THE FOUR WHEEL CYLINDERS TO TWO ACCUMULATORS.
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