this is done, so as to increase friction between the road and the tyre to ensure better grip to prevent accidents while suddenly turning or suddenly applying brakes
they are made corrugated and rough because if they will be smooth and break would be applied their would be less frictions and the vechile may not be stop fast and may it could lead to a accident
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S Ramaratnam answered this
This ensures a better grip with the surface of the road due to the added friction
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Debabrata Sahu answered this
Te tyres are usually made rough due to increase friction with the ground. If the tyres would be made smooth then the tyres would not get required friction with the ground and can't work easily.