I did some more digging and this is what I found:
About That Little “a”
The small “a” following Ziex CT60 indicates that this is an OEM-specific fitment. Meaning that Falken makes these tires specifically for Mazda. Such OEM-specific tires generally have a shorter than typical tread life. We would estimate, based on measuring the tread, that the tires will last about 35,000 miles before changing them would be wise. OEM-specific tires are designed for optimum affordability and fuel efficiency. If you purchase CT60 tires without that small “a,” you will find that the tires offer a much longer tread life. All of what I have just said in this paragraph is typical of OEM-specific tires and is not unique to Falken. You can follow us as we test the aftermarket version of the Ziex CT60 A/S tire here at Torque News.