What STI considers to be a ‘car that drives well’
Subaru’s works-based tuner, STI, has long been consistently proposing a “car that makes driving better”. This means that it is important for the car to move linearly and without time lag from operation.
The key is to make the inner wheels usable with minute steering
If there is a time lag between when the driver turns the steering wheel and when the car reacts, the driver will unconsciously turn the steering wheel more and more. When the car starts to react, the steering angle is large and the car rolls at once. This causes a large rolling movement, which is unstable. Passengers are also likely to feel uncomfortable.
At the same time, a slow response to the operation makes the driver feel uneasy. Just as you would break out in a cold sweat if you turn the steering wheel on a snow-covered road and the car goes straight ahead, so too does a delayed response to controls lead to a sense of fear.
In other words, reducing the time lag between maneuvers and ensuring that the car moves linearly can eliminate a sense of unease. It also prevents the steering wheel from being turned too far, allowing the car to turn in a stable and natural posture. In other words, the driver can feel that they are driving better.
To achieve this, it is important not to mistake the meaning of linear. Linear means that the car responds promptly to the controls, which is different from being overly sensitive to the controls.
STI particularly focused on the use of the inner ring this time. In particular, the use of the inner ring when the steering wheel starts to turn. When a car is about to turn, the load is applied to the outer wheels by centrifugal force. However, if you rely only on the outer wheels, the limit becomes low and only the outer wheels are crushed, resulting in jerky movement.
Therefore, the inner wheel moves ahead of the outer wheel, enabling smooth cornering.
The force of the inner wheel only occurs for a moment. The uniformity of body rigidity is important for how that moment can be used. If the rigidity of the entire body is well balanced, the inner wheels can be used to start the turn, and the car’s response to minute steering angles will be better.
It doesn’t increase body rigidity, it balances it
This is where STI proposes “flexible” parts. The aim is not to increase rigidity, but to improve the rigidity balance to make the car respond more linearly.
The Flexible Draw Stiffener is a part that eliminates play by pulling on the body and suspension with spring force, and aims to speed up the car’s response.
In the Impreza tested this time, it was installed in the rear bumper. By pulling the rear ends of the left and right rear frames towards each other, tension is applied to the body, thereby increasing the response to the driver’s maneuvers. Since increasing body rigidity only in one part of the body would result in an imbalance, this part is designed to respond quickly to inputs by providing tension to the frame while keeping an eye on the overall structure.
In addition, a ‘flexible tower bar’ is fitted at the front. Tower bars are generally used to increase rigidity by connecting the left and right strut towers in the engine compartment. However, with this flexible tower bar, a link ball is inserted in the middle of the bar connecting the left and right sides. Therefore, it does not increase the rigidity of the body, but has the effect of supporting the left and right strut towers.
The bar moderately resists inputs from the road surface, while holding firm during cornering to achieve strong and supple characteristics.
Regrettably, we were not able to do a comparison test drive on the same vehicle this time, but we were able to experience the handling that seems to be the effect of the Flexible Parts Series when we test-drove a vehicle equipped with the system.
Since the steering responds very slightly from the start of turning, it is difficult to feel uneasy even when diving into corners at high speeds on a closed course. You can smoothly change direction without feeling any understeer when cornering, or any increase in rigidity as when a tower bar is fitted.
I recommend these parts to people who do not have many opportunities to drive a car regularly or who are not confident in their driving skills, as they make driving a car easier.
translated by DeepL