 It is legal and permissible for a tire manufacturer to give a particular tire line a lower treadwear grade.For example, if the highest treadwear grade in a manufacturer's lineup is 600, then a tire line with a lower treadwear test result might receive a grade of 400, instead of the 480 it could possibly receive.Also, it is common for tires whose treadwear grade is of little commercial value, such as racing tires, to be assigned extremely low values - sometimes even zero.