The limited-slip devices, which resemble multiplate clutches except that they are pressed together by hydraulic pressure instead of springs, are controlled by a computer that monitors four wheel- speed sensors—one per wheel. If the computer detects any wheelspin, it progressively applies either or both of the limited-slip clutches to redistribute the power. The computer also monitors longitudinal and lateral acceleration sensors and applies the rear-differential clutch when the throttle is closed during hard cornering—increasing understeer. For maximum stability, both locking devices

automatically disengage under braking. For maximum starting traction, both can be locked by a driver-activated switch; the clutches then automatically disengage when speed exceeds 25 mph.

The entire dnvetrain is one unitized assembly. The rear-mounted engine feeds power forward to the transmission, which in turn spins the center differential. From there, one dnveshaft runs back through the transmission’s hollow countershaft to the rear differential, located between the engine and the transmission. Another driveshaft runs forward to power the front differential. This drive

shaft runs within a tubular housing that rigidly connects the front differential to the rest of the powertrain.

Packing this hardware into the confines of the 911 shell required not only a new floorpan but also a redesigned suspension. The front suspension, altered to accommodate half-shafts, remains a strut design, but it now uses coil springs instead of torsion bars. Because much of the four-wheel-drive system’s 220 pounds is up front, power-assisted rack- and-pinion steering is standard.

In the rear, the Carrera 4 uses a redesigned semi-trailing-arm suspension,