1/4 mile at a time at higher than rated speeds is pretty safe. UNTIL you are getting into the 120 mph range. STILL run load rated tires FOR YOUR VEHICLE WEIGHT!!!! It is the 'extended' time at speed as well as the ambient/ road surface temps is what are tire killers. A tiny 'overloaded' tire on the street is NOT recommended even though most of us(me included multiple times) have done so. Even more dangerous is running a spool on the street with tinys up front as you can do serious tire sidewall damage at low speed 90 degree turns and or pop 'em off the rim altogether.