BC Racing Coilovers - ER Series Coilover for 02-07 SUBARU IMPREZA WRX (F-02-ER)BC RACING ER SERIES COILOVER KIT 02 07 SUBARU IMPREZA WRX Part Number: F 02 ER The WRX ER Series coilover from BC Racing Is the perfect setup for the dedicated track racer. ER stands for External Reservoir. This series includes all the same features of the BR series along with the RM series, with the key difference between the ER and the others being an External Reservoir. The External Reservoir holds many advantages over the other series coilovers