Quote Originally Posted by mcjimmy33 View Post
15x12 you will run higher RPMs. I run a ACME 2313 which is a 15 x 12 but with .150 cup to keep the RPMs down some at higher speeds. Switching from a 15 x 13 to a 15 x 12 will get you more torque and low end power and sacrifice top end speed.
You will likely run lower rpms surfing though, because the engine doesn't have to work as hard and the prop isn't "slipping" as much.