D2 PRO Lowering Springs 1.6"F/1.5"R Sonata / Optima 2011+ D2 PRO lowering springs optimize and improving handling characteristics and offer a reduction in ride height while maintaining exceptional ride quality through a progressive rate spring. All of our springs come with a lifetime warranty and are manufactured of 55 chrome silicon steel in an ISO 9001 and TUV approved facility. Includes lifetime unlimited mileage warranty