Just look at how much simpler a MacPherson rear suspension is. The rear lateral link pivot axis is almost parallel to the ground, resulting in less binding resistance as torque is applied and therefore has minimal anti-squat. Having disc brakes, even on the base Impreza, is nice too.
Front Suspension
The front suspension on the previous-generation Impreza and WRX had some unpopular traits. Its steering was plagued with a numb on-center feel and a poor return to center when cornering. High-power modified WRX models have a hint of torque steer and a large amount of anti-dive/lift geometry. This leads to a non-linear build-up of understeer when trail braking and when on the throttle at corner exit. Compared to the turn-in of its rival, the Lancer Evolution, the WRX felt considerably less sharp.
Subaru's engineers have been working on these issues. At a glance, the front suspension appears to be identical to the old car (the tried-and-true MacPherson strut design), but there have been many subtle changes in front-end geometry-the most notable being more positive caster and a greater steering axis inclination angle.
The '08 Impreza rear trailing arms' bushings resist braking and engine torque loads, but have enough compliance to allow the toe link to steer the tire inward under roll. You can also see the position of the upper control arm. To clear the frame rail and the coilover shock absorber, the upper arm had to be cast from steel. Although it's an expensive process and results in a heavy part, it would have been difficult designing a stamping to snake through this limited space. Note the bosses for a disc brake caliper in this drum-equipped car. You can also see the mounting boss for a rear anti-roll bar.
Both changes increase straight-line stability, on-center feel and steering return to center. Increasing positive caster also improves turn-in and contributes to negative camber gain as the steering wheel is turned off-center. In addition to improving on-center feel and straight-line stability, increasing the steering axis inclination angle moves The Dave Point closer to the center of the front tires' contact patch, reducing the tendency for torque steer and steering pull when accelerating or braking over two surfaces with different levels of traction.
The most amusing thing is that all the changes Subaru has adopted are already popular modifications performed by top tuners on the current Impreza. We wish the new multi-link rear suspension had found its way to the front, but realistically, any multi-link would be difficult to package, due to the width of the boxer engine.
It also appears that the new car has less anti-lift and anti-dive incorporated into the front suspension geometry, as the front lower control arm is more parallel to the ground than the older car. This change is well known in the aftermarket, featured in many popular anti-lift kits that relocate the rear pivot of the lower control arm, reducing anti-dive and increasing positive caster at the same time.
The front suspension is basically the same as before, a simple MacPherson strut with geometry improvements. From the side, the new lower arm pivot points are more parallel to the ground, taking out much of the anti-dive from the old geometry. The new car doesn't have the U-shaped steel brace (highlighted in red) that buttons up the entire front end. The front wheel moves forward, relative to the engine, shifting weight further behind the front axle as well as adding caster to the front struts. Also, notice how far back the new firewall sits on the left, as well as the increased width of the transmission tunnel. This is what you will keep bashing your foot into when you try to heel-toe in the new Impreza.
Driving Impressions
Due to our limited time with the new car, our driving impressions were confined to a short street drive-not the place to conduct handling evaluations. So we had to be content with some mild seven-tenths driving to get more of a general feel of the differences. As we expected, the new car has greatly improved steering feel. The center is less numb, with more definition and the steering wheel centers itself crisply when recovering from a turn. There is not a hint of torque steer, but, with a naturally aspirated motor, there isn't as much torque to induce any. Turn-in response is more immediate-nervous almost, on such soft suspension and hard tires. But so far, a general thumbs-up.
On the throttle, the new car exhibits very little squat. This was the complete opposite in the previous-generation Impreza, as that car had less dive under braking and more rear squat under acceleration. Although neither base car have anywhere close to enough power to break the rear tires loose, the new one feels more connected and solid in all attributes, except for an annoying tendency to dive under braking. On a non-suspension-related note, the new car also has an improved braking feel with a harder, higher pedal and better modulation. But the older Impreza, with a slightly stiffer suspension, still feels like more like a driver's machine compared to the new Impreza's high-precision, but soft econobox feel.
These suspension changes are a good step forward for overall performance and safer driveability for the masses. The aftermarket can easily address brake dive with stiffer springs and improved dampers. Changes to the front-end geometry basically mimic what top suspension tuners are already doing to the old car, making for a much better base platform from which to build. In the rear, we can expect the new suspension to improve traction and the aftermarket will quickly find interesting ways to optimize it for performance driving and motorsport.
The new rear shocks sit far more inboard than the struts of old, which attached to the hubs themselves. This gives the suspension a different motion ratio.
We can't wait for the upcoming STI to see what the changes feel like with some real power behind them. A new project WRX or STI might even be in the works for us some time soon. If that's the case, then we'll really wring the all-new Impreza by the neck and give you a blow-by-blow account of what works and what doesn't.