A tire's speed rating depends on how long it can safely perform at a given speed. As a tire is driven faster and faster, it generates heat, which can deform the tire structure. High-speed tires are designed to resist these deformities at the speeds they are rated for. Resisting deformities means controlling heat buildup. The only way to do that is through innovative belt design, which all tires have as appropriate to the speeds they are built to handle. Tire speed ratings are designed to let the driver know what speeds are safe--not as a suggested guideline that can be exceeded with no worries. Safety is the major concern with such rating systems, exceed the recommended tolerances at your own risk. Tire companies assume no liability for accidents caused by exceeding the rated speed of a given tire.