AST 30mm/20mm E90/E91 Lowering Springs | BMW 3 Series Touring (E90/E91) (ASTLS-14-391)AST Lowering Springs for the 2005 2012 BMW 3 Series (E90 E91) are manufactured from a premium high tensile chromium silicone wire which is handpicked by AST engineers for its quality and metal consistency. Each spring is cold wound and then heat treated to increase hardness and reduce internal stresses present after winding. Each spring is then individually shot peened, phosphate treated and then powder coated to outlast even the life of the vehicle.