Actually, less contact area doesn't equal to less friction. I got into this arguement with my friend, and found that this was wrong. Here's why. When you have less surface area to be acted on, you'll have more force per square inch to be counted for. So, when you have less surface area to act on, there are actually more frictional force on the remaining area which will turns out to have the same net frictional force. The easiest way to visualize it is to wrap a block of wood with sandpaper, then measure the force it takes to push it laying flat on the ground; then measure the force it takes to push it laying sideway on the ground.
But, because of the added stress, the cross drilled rotors will probably not last as long.
Originally posted by DemonSVT:
Less surface contact area = less friction = less stopping power. (simple physics)
It also equals significantly lower rotor life due to cracking from the heat cycles.
