Hello! I need the first time for my Astra new tires. Therefore also the theater… According to Schein und Brief: 215 50 r16 W 215 40 r17 Y Max Speed 245 km/h Why is a W tire (260 km/h) sufficient at 16 inches, while I have to buy a Y tire (300 km/h) on 17 inches.Of course I ordered a W tire at 17 inches and now I have to watch how to send it back and order Y. My question: WHY?