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.
Today most tires are pneumatic tires, though typically still referred to as just tires. The word pneumatic simply means an item that uses air. Tires work because they have tread on them. Tread is the raised patterns that appear on the top of a new tire, which often appear to zigzag around the tire. The tread helps the tire gain traction on the road to prevent it from sliding.