The stock rotors measure 11 inches and the rotor for the 16-inch kit is 1-inch bigger at 12 inches. Just like an engine, it is all about torque. It's easier to loosen a tight bolt with a breaker bar than a 1/4-inch-drive ratchet, and the same idea applies here. The further from the axle centerline you move your friction material, the more effective it becomes. Bigger brakes always work better, thanks to physics.