Question

Automobiles tyres have generally irregular projections over their surfaces. Why?

Answer 1

We know about a force, which acts on a moving body opposite to the direction of motion. This force has minimum value if the plane of the surface is smooth.

Complete step by step answer:
To understand this, we must know something about a term called friction. Friction is a force between two surfaces that slip over each other, or attempt to slip. When you try to manoeuvre a book around the board, for instance, friction makes this impossible. In the direction opposite to the direction in which the object is travelling or attempting to travel, friction always works.
There are two ways to improve friction: one is by making the surfaces rough, and the other is by increasing the mass of the moving material. The tyres of cars, for example, have treads (these are the 'designs' that can be seen on the surface of the tyre), which improve the friction between the tyre and the road.
In addition, car tyres have irregular predictions on their surfaces such that friction between tyres and the ground is enhanced. This boosts the grip of the on-road tyres. For reference, a vehicle undergoes circular movement when taking a right. Thus, a power equivalent to the centrifugal force the car needs to be worked upon. The frictional friction produces this force which works on the car.
The irregular projections thus increase friction between the tyres and the ground and avoid skidding of the car.

Note: There are different types of tyres with different types of grips for different purposes. If you are off-roading then have to choose such a tyre which is different from a tyre used for city rides.