The light falling on the surface of a convex mirror diverges ( for rays coming from the objects far from the mirror).
As a result, the objects appear smaller and closer, providing important information to the driver of the car by providing a better picture of the vehicles behind him.
A convex mirror also provides a greater field of view.
Final Answer:
Hence, convex mirror is commonly used as rear – view mirror vehicles because it always forms an erect image and gives wider field of view to the driver.