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.
What does the tire tread do? On a normal, smooth road, the tread has only limited influence on the riding properties. The grip generated by the tire on the road is almost exclusively the result of the rubber compound. Unlike a car, a bicycle will not aquaplane. The contact area is much smaller and the contact pressure is much higher.