Tire speed ratings are determined in laboratory testing. These ratings are also evaluated by consumer groups and car enthusiasts-people with a vested interest in knowing the exact limitations of their equipment. One fact often overlooked about tire speed ratings; these ratings apply to undamaged tires only. There is no way to determine the tire speed ratings on a damaged tire as each kind of damage produces different results. It's best not to attempt any extended or "at speed" driving on damaged equipment. When your tires are compromised, it creates conditions suitable for potential additional damage. Pushing your tires too hard in such a condition makes for unsafe driving. This caveat also applies to altered or modified tires. No data is officially available on the tire speed rating based on such modifications.