The Bilstein B8 rear shock absorber (MPN 24-115957) is a gas-pressure monotube damper from the B8 Performance Plus line, built to replace the rear damper on a BMW 1 Series 120i. Monotube gas-pressure construction is the core of the design, and the B8 is positioned as a sport-tuned upgrade rather than a comfort-first replacement. Compared with a stock shock, it offers firmer, more controlled damping when the car runs lowered springs or a production sport suspension. Compared with a budget twin-tube, the monotube layout is the main reason to pay the difference.
Enthusiasts searching for "E87 120i rear monotube shock," "BMW 1 Series lowering spring rear damper," or "Bilstein 24-115957 E87 fitment" will find this part's application listed for the E87 120i. Fitment data lists it for that model from late 2003 through 2012, but other listings show it for 128i and 135i models from 2008 to 2013. Confirm your exact model and build date by VIN before ordering. Because the absorber carries no spring itself, the coil spring is a separate component to plan around during removal and installation.
This is a rear shock swap, so plan for basic hand tools, a jack and jack stands, and access to the rear suspension. Before ordering, compare the mounting ends of your old shock with the new unit, since one catalogue lists top and bottom pin mounts while another lists stem mounts. Because the coil spring is separate from the absorber, confirm how the spring sits and how it is retained before you disconnect anything. Torque specifications and the exact removal sequence were not confirmed in my research, so use the BMW service information for your model year.
