The Bilstein B8 Performance Plus rear shock is a monotube damper for Subaru WRX and WRX STI owners who have fitted lowering springs and want damping that suits the changed ride height. Bilstein positions the B8 Performance Plus as an upgrade over factory dampers, and the design combines gas-pressure monotube construction with valve settings tuned to each application. Each unit is road and track tested and held to quality standards that meet or exceed OE specifications. Against a budget shock, that application-specific tuning is the main reason to pay more: on a lowered car it helps keep the rear end controlled over bumps instead of wallowing or bottoming out.
Buyers searching for a 2015 WRX STI rear monotube upgrade or a Bilstein B8 for lowered WRX use should confirm fitment before ordering. The product name lists 2015-2017 WRX and WRX STI models, but fitment tables for part number 24-249508 vary and extend into later model years. Confirm the application for your specific trim and drivetrain with the manufacturer before you buy. Installation is within reach of a capable home mechanic with basic tools, provided the rear suspension is properly supported and checked once the car is back on its wheels.
Plan on a hoist or sturdy jack stands, a torque wrench, and new self-locking nuts, since the manufacturer's general performance-suspension instructions say self-locking nuts must only be used once. Disconnect the negative battery terminal before starting. Leave rubber-mounted shock attachments loose until the car is loaded with its wheels on the ground, and tighten other brackets and fasteners before that point. Avoid impact tools, which can damage threads. After the work is done, check that the vehicle's movement is unrestricted with the lowered suspension, then verify alignment and headlight aim.
