Taller tires have the same effect as putting on a smaller rear sprocket or a larger front sprocket. No matter what you do to your tires it will not effect the horsepower output of your motor . It will effect how the horsepower is used and at what RPM it is used. It takes more horsepower to spin a taller tire than a shorter tire for many reasons. The main reason is, as stated before, a change in gearing ratios.