back to the original question, tire speed ratings are for *sustained* speeds. All tires can go beyond their speed rating safely, but are not recommended for long runs at higher speeds. no one will define the time before safety is a concern, but it is much longer than most people would spend at higher speeds typically
This is why, for example, drag race tires would never survive a sustained high speed, but can see extremely high speeds safely for short distances
As for drag:
http://www.hotrod.com/techarticles/h...o_tricks_tips/