2008 Subaru Impreza STI - Chassis Design

Capitalising on the Boxer engine's inherent low centre of gravity and symmetrical weight distribution gives the Impreza range a superb natural chassis balance. The STI takes this even further with its' revised power delivery and advanced control systems that have been honed on years of proven motorsport history.

The new silver centre console now houses the controls to the revised Driver Controlled Centre Differential (DCCD). Subaru have changed from their traditional roller dial (first seen on the 1997 STI3 Coupe) and replaced it with a neat button and bar combination. When you press the button to shift the DCCD from Auto to manual model the LCD display on the dash changes. Nudging the bar up and down changes the number of lines displayed on the screen, the lines clearly represent the % of Torque be transferred between the two axles.

In its' default Auto mode the STI sends 59% of the torque to the rear and will shift power forwards depending on the information it receives from a number of Sensors. The DCCD can adjust torque as needed up to 50/50 Lock which physically locks the front and rear axles together to give maximum traction. When the driver chooses Manual model they are able to select the Torque distribution themselves without any computer intervention. This can be very useful when driving on a circuit (maintaining rear bias) or if the car needs to find grip in snow etc (50/50 Lock). This advanced Differential control is designed to give the driver complete control over the cars power delivery under different environments resulting in a more intuitive and rewarding chassis balance.

The Japanese STI also gets Subaru's ultra quick and responsive 13.1 steering rack which adds great weight and steering feel for the driver. The rest of the world will receive the same rack as the WRX/GT models at 15.1.

The new multi-mode Vehicle Dynamics Control (VDC), which is Subaru's advanced traction control system, also provides three different modes that the driver can choose from to experience a wider range of driving enjoyment, while always maintaining the safety features of VDC.

NORMAL mode: The standard mode controls ABS, TCS and VDC.

TRACTION mode: Adjusting both TCS and VDC, this mode extends the time period until the VDC kicks in. This mode is suited for sporty driving as it does not control torque-reduction in the engine.

OFF mode: This mode only controls ABS. It is used in emergencies like getting the vehicle out of deep snow or mud.

The WRX STI boasts a state-of-the-art chassis design. Equipped with a strut-type front suspension and the newly designed double-wishbone rear suspension, and combined with its widened track, this model achieves outstanding cornering stability. Optimized suspension geometry settings with adjusted camber angles have made substantial improvements in road-holding traction and riding comfort. Aluminium cast lower arms and a stabilizer bar in the front suspension help raise torsional and rolling rigidity, providing accurate response in steering inputs. In the rear suspension, suspension links are attached to the body through the sub-frame, which enhances riding comfort and further lowers noise levels. The Boxer engine is mounted lower on the chassis (22 mm lower at the front end of the engine, compared to the previous model), further advancing vehicle stability already ensured by its low centre of gravity.

The Brembo ventilated disk brake system employs an ultra-low expansion brake hose and tie rods for the brake booster. The brake system, coupled with the SuperSports ABS (antilock brake system) with EBD (electronic brake distribution), processes information fed from the G sensor, steering angle sensor, yaw rate sensor, and pressure sensor to deliver steady braking and control. It also works with the DCCD system to ensure accurate braking on all four wheels independently, while minimizing deviations from the driver's intended path. Bridgestone RE050A (245/40R18) tires are standard from Subaru. The hill-start assist function maintains the braking function one second after the brake pedal is released in case of starting a car on a gradient.