The 2008 WRX STI features an enhanced version of the DCCD All-Wheel-Drive system. DCCD is one of the most advanced and most performance-directed AWD systems on the market, regardless of vehicle segment. The system employs planetary-type differential gears with a nominal 41:59 torque split. A mechanical limited-slip type center differential augments the electronically controlled differential to enhance torque transfer performance. Steering sensor input improves torque transfer response by accurately relaying the car’s cornering situation. Lockup is controlled by the Transmission Control Module, with setting selected by switchgear on the center console.
Set in Auto mode, the electronically managed continuously variable transfer clutch can vary the torque distribution ratio in response to driving and road-surface conditions. Auto mode provides the best all-around performance for most drivers and circumstances. The system determines the ideal power distribution in response to vehicle acceleration, deceleration, steering angle, cornering force, and wheel slippage.
The three Auto modes are:
- Auto – the same as in the previous STI model.
- Auto [-] – shifts the torque bias to the rear and reduces the center limited-slip differential lock, which allows sporty driving on high-traction surfaces.
- Auto [+] – for driving on slippery surfaces, such as gravel or snow, the setting increases limited-slip differential lock.
The six manual differential locking settings remain the same as in the previous model. In manual mode, DCCD allows the driver to vary the front-to-rear torque distribution (up to 50:50 maximum) to optimize AWD performance for varying driving conditions. The driver first selects manual mode with a console-mounted button and then pushes or pulls the rocker switch on the center console to select from six levels of center differential locking. Increasing the lock factor sends more power to the front wheels, which the driver might want in certain driving conditions or to suit an individual driving style. A helical-type limited-slip front differential and TORSEN* torque-sensing limited-slip rear differential optimize power distribution side-to-side, helping to prevent the inside wheels from slipping during cornering.
Read more about DCCD in Version 1.2 of Subaru Drive Performance magazine.