Well, I just got back from a two day test ride of my nine with both pulley's and 170-80 rear tire. I was very please, felt like a true overdrive. Speedometer is off about 5 mph to the slow side while mpg jumped to 51 over a two day hard ride in all types of conditions one would encounter. Fourth actually feels like the former fifth. I don't know if I would recommend this but it is smoother at a higher speed and I felt the difference in the rear tire. I had to get used to the new handling......This was documented with the GPS test bike and the mpg was based off of the GPS and not my bike. I used his mileage and my gallons used to compute. I am getting back to you as promised took a while due to weather.