What are the pros and cons of putting different tires on the front and back wheels, especially for commuting over rough pavement and potholes? Is this even done or do people always get matching tires? I'm thinking of putting a road tire on the back wheel when the current tire wears out, but the front tire is still going to be in really good shape. These tires are wide ATB-type "city"...is putting a rear tire on that's a different size unsafe or will it make the bike handle poorly?