Hello, I'm looking to convert my fat tire bike to mid drive motor. It has a 11-34 tooth 7 speed freewheel. I ride mostly gravel roads. There are some occasional long 15 degree or so hills. I don't need a speed machine just want to make it up hills without putting stress on motor. I weight 230 and like I said before I only cruise around 10 mph. My question is what front sprocket size should I buy with motor?