Tire speed ratings give no real indication of how a given vehicle might perform at these speeds. Remember that your engine, suspension and fuel consumption play a major part in how the vehicle operates at speed. In some cases, it is conceivable that you could damage your engine before reaching the maximum rated speed for your street-legal machine. Race cars are built differently and made to last; consumer vehicles react differently to this kind of abuse depending on the duration and frequency of excessive speeds. Your tires may be able to handle much higher speeds than the rest of your vehicle is able to endure, and there are no guarantees as to how your vehicle may be affected at those prolonged higher speeds.