Supposedly the rating on the sidewall has a safety factor of 1.5, the worst tire in a batch is not supposed to blow off the rim when inflated to 1.5X the sidewall rating, so for a 70 PSI rated tire you can pump it to an actual 105 without worrying that it will blow off the rim. The only problem with that is that rim blowoff is the least likely failure mode from overinflation, but it is the most spectacular. You could take a 70 PSI rated tire to 85 or 90 if conditions warranted that kind of pressure and you didn't actually go slower because the tire wasn't rolling on the road any more but was just bouncing above it. Coast down tests are a good indication of proper inflation because low speed rollout is more affected by rolling resistance changes than by aerodynamics.

Quote from richardr on Jul 4^th, 2010, 12:02pm:

 
Schwalbe Kojaks although they are 1.35, rated at 95 although I always run them at 100