Only the “SI-DRIVE” advanced driving control system makes this possible. A single switch can be used to select one of three driving profiles by altering engine and transmission computer ‘maps’, changing the way they interact in terms of factors such as gear change characteristics and throttle response.

Intelligent:
Gentle power delivery. Ideal for stop-star traffic, covering long distances, or for driving with fuel efficiency in mind. Provides outstanding control in the wet or on unpredictable surfaces.

Sport:
Highly responsive with direct acceleration. In addition to being suited to all-round conditions, this mode puts the enjoyment back into high-speed cruising, or negotiating winding roads.

Sport Sharp:
This mode makes full use of engine power, offering instant acceleration and sharp response. Ideal for merging or overtaking on motorways, or for enjoying sporty driving anytime, this mode unleashes the maximum potential of the vehicle.

MULTI MODE DCCD
A cutting-edge, electronically controlled AWD system exclusive to the WRX STI that incorporates a torque distribution planetary gear in the centre differential coupled to an electronically controlled LSD mechanism that automatically limits slip between the axles. With Multi-mode DCCD, the control module can detect more precisely the driver’s intentions with regard to how much they want to turn the vehicle. With the help of the mechanical LSD, the control module is able to manage the electromagnetic LSD at the right moment without affecting the driver’s intentions. For the same purpose, the static torque distribution ratio between the front and rear axles (before the LSD is active) has been changed from 35:65 to 41:59. Inputs such as the speed of each wheel, throttle opening and longitudinal and lateral acceleration determines the optimum level of torque distribution and differential lock. This allows the driver to control the WRX STI sports performance as they please.
In addition to the default automatic mode, a selector switch enables manual operation, with a choice of five settings, progressively sending more torque rearward.

VDC
With Subaru’s Vehicle Dynamic Control the driver’s inputs are constantly monitored sensors on the steering, throttle, gearbox and brakes. This electronic control system takes this information to constantly and automatically optimise traction and stability with a computer. Torque distribution between the front and rear wheels is optimised, torque distribution between left and right wheels is controlled when braking, and engine output also controlled in a flash, without hindering the sporty driving required by the driver, all to maintain a safe level of driving.
VDC is an intelligent electronic control system that brings driving conditions and vehicle behaviour close to the driver's ideal settings and achieves this by determining driving conditions and the driver’s intentions with a computer, and then controlling understeer and oversteer through braking control on each wheel and a limit to engine power output.

Suspension
The challenge for any chassis engineer working in the series production car environment is to find an ideal mix between comfort and roadholding which is appropriate for the vehicle’s target market. One of the most important parts of this balancing act is the choice of suspension systems, and Subaru’s sophisticated double wishbone rear suspension is now fitted to every model in the line-up. The system increases contact between the tyres and the ground by keeping the wheel perpendicular irrespective of the load being exerted in the suspension, and negotiates bumps in the road surface smoothly for supreme ride comfort. Handling has also been improved by increasing contact between the tyres and the ground at the front of the vehicle, with an increase in mounting rigidity of the more conventional front strut suspension.

Overall, this provides a sense of security and stability, and the vehicle seems to hug the road. Sure-footed traction is assured, even on rough road surfaces or when cornering, and is linked to safer, more enjoyable driving.

Highly Rigid Body
A highly rigid body is required both to meet safety requirements and for the suspension to work correctly, while performance and fuel consumption is directly affected by the weight of the car. To best achieve these divergent requirements Subaru has created a stiff yet lightweight body by selectively using aluminium materials and high tensile steel plates throughout the vehicle.
For better safety in the event of an accident, Subaru has implemented its own technical development based on examinations of actual accidents. One of the most significant results that benefits protection in all directions is the “Ring-Shaped Reinforced Frames”. Each pillar - including the centre pillar, body side frames and floor crossmember are positioned in a ring-like layout, all connected to form a protective shell.

In addition to this is the unique structure of the front of the vehicle, made possible by longitudinally mounting the horizontally-opposed engine. The side frames extend straight from the cabin to the position of the bumpers in a symmetrical manner to create a frame layout that absorbs energy from frontal collisions effectively. These qualities all ensure that the Ring-Shaped Reinforced Frames provides a balance between protecting against collisions and controlling energy dissipation, from any direction.