Perrin PSRS Offset Bushings - STI 2011-2014
P.S.R.S stands for Positive Steering Response System and simply replaces the front control arm rear bushings. The OEM bushings are designed to be extra compliant to reduce noise, vibration, and harshness (NVH), and make the ride more comfortable. The compliancy of this bushing is not something a performance oriented driver is looking for. Eliminating the OEM super soft bushing provides significant improvement in how the car steers during hard cornering and even in a straight line.
Under braking and acceleration, the OEM bushing can flex enough for your wheel to move back and forth .500"! This deflection of the wheel causes drastic toe in and toe out changes under braking. The toe changes will cause steering wandering and an altered tire contact patch. When accelerating, this OEM bushing causes unwanted wheel hop and the car will want to follow the ruts in the road.
Under braking the wheel will have zero deflection after the PERRIN PSRS is installed. Since there is no way for toe changes to occur, the steering feedback issues and wandering under braking disappears. Under acceleration the car will have far less tendency to follow the ruts in the road, wheel hop will be eliminated, and in turn the car will have more front-end traction.
The bushing in the PSRS is purposely offset from center-line. This adds approximately 0.5 degrees of caster to the front suspension. Caster is the angle on which the steering knuckle rotates. Adding caster makes the car turn in faster by providing a larger contact patch as the wheels turn on the steering axis.
A byproduct of the PSRS kit is that it reduces some of the built in "anti-lift" that Subaru builds into the suspension geometry. Changing the geometry toward a Pro-Lift setup which means there is more weight transfer happening under acceleration and deceleration. During acceleration this helps transfer weight to the rear of the car creating additional traction for the front tires, which reduces understeer. Same thing happens under braking.
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