I have a set of nangkang tires, but they aren't z rated. these are the cheapy 14in directional tires. They are supposedly "economy perferomance" tires. All i have to say is that these tires do not wear at all. My friend has had them for 2 years, i've had them for a year with bad camber and there is barely any wear on the tires. Point is, NangKangs are cheap tires. Don't expect too much from them.