The primary contributor of skin color is the pigment known as melanin. The quantity of melanin in the skin varies based on genetic factors and is also dependent on the degree of sun exposure. Melanin is produced by specialized pigment cells known as melanocytes.
Average new tires used on cars typically start with 10/32 to 11/32 of original tread depth. Tires are considered worn out. In most States when they reach 2/32 of remaining tread depth. Ans 2 - Here in Canada (and I'm sure in many parts of the US ) we get a lot of rain.
A NASCAR tire is only about 3/32 of an inch thick, which is why the wear holes are so important. And for some tracks, including Richmond International Speedway, Homestead-Miami Speedway, and Texas Motor Speedways, Goodyear uses two different compounds on the same tire, called a multi-zone tread.