HAWK HB432D.661 Front Brake Pads ER 1 Endurance Racing for SUBARU Impreza 2004 2010 ymm_7 The standard spring option is ymm_37 The standard spring option is for customers who wish to replace a broken idle spring in their twin piston atmospheric dump valve The Triple Pass Flow Structure allows the coolant to flow across the core of the radiator three times before exiting for lowest outlet temperatures possible This consistent performance over long periods makes the ER 1 suitable for endurance racing The ER 1 compound was developed by Hawk Performance for the endurance racing market with the goal of providing a higher coefficient of friction than competing endurance pads while maintaining equal or improved lifespan