Why the wear and tear of outside roller bit would be bigger than inside bits for core barrel core foundations piling

Generally speaking, the dia. of outside roller bit would be bigger than that of inside, so it is same for the perimeter.When piling in the same depth and in a same circle, the outside rock perimeter is longer where the bits need to cut through.Comparing with smaller perimeter of inside, the wear of outside bits would be bigger.

Core Foundations Piling

barrel core muscles

core series barrel