I have 31's right now, but I don't know what size I will end up with because I am switching to paddles on the back, with stagger, that way when I hammer it , it will look like one of those speed boats with the cool prop on it that shoots water a mile high. The trans that came with the motor if connected to the rear end in it now would probably give me a gear ratio for vertical climbing. When you look at it, that's the first thing that comes to mind, spin the motor and make a coupler from the existing drive shaft axle hanging out to the rear end. I could probably take off in 5th gear, doing a wheely of course.