Treadwear grades are an indication of a tire’s relative wear rate. The higher the treadwear number is, the longer it should take for the tread to wear down.
A control tire is assigned a grade of 100. Other tires are compared to the control tire. For example, a tire grade of 200 should wear twice as long as the control tire.
Of current tires:
15% are rated below 200
25% are rated 201 – 300
32% are rated 301 – 400
20% are rated 401 – 500
6% are rated 501 – 600
2% are rated above 600