BC Racing Coil Over Shock Absorbers EG models. ER Series Coilover : Type ER For Professional Track Specifications Top Mount Type : Pillowball Front, Pillowball RearER Front Spring Rate : 12kg/mm (672lbs/in) Rear Spring Rate : 6kg/mm (336lbs/in) Information BC Racings premium flagship coilovers are the external reservoir ER Series with separate compression and rebound damping adjustment. The ER Series coilovers bring with them the high quality and unique features seen on the BR and RM type but have the additional benefit of external reservoirs and the ability to allow the end user to individually adjust and set compression and rebound damping rates. The external reservoir ER Series coilovers allow BC Racing to increase the oil capacity of the damper unit. The additional oil capacity reduces peak oil temperatures which decreases variations in damping rates due to oil viscosity changes. The reduction in damping rate variations improves handling and ultimate on road and track performance.