[BigAls87Z28]

What most tire manufactures do is comprise tires of 2 different compounds, the first layer is of a sure grip compound but since there is a lot of tread, it uses the deep tread for good contact. After about 50% wear, you break into the 2nd level of rubber that is even better for grip to keep the same if not better traction then you had whent he tires were new, therefor never giving the driver the feeilng of a poor tire after 50% worn.