The Michelin Pilot Sport 4 S 355/25r21xl is a high-performance tire designed for sports cars and luxury vehicles. It features an asymmetric tread pattern that provides superior grip in wet and dry conditions. The tire also has a unique rubber compound that helps it perform better in extreme temperatures. It also has a reinforced sidewall for additional protection against impacts. The Michelin Pilot Sport 4 S is a great choice for those looking to improve the performance of their vehicle.