this 15 t and stock rear sprocket. Now the bike is perfect. I was happy with the power but the bike did feel asleep at say, 3400 rpms if you were to just lay into it. Now it has a power band similar to a liter bike. It just pulls nicely from just about any rpm. The throttle is actually less jerky now, which surprised me and is much more enjoyable in town and on the hwy. My rpms didn't raise by much ( 60 mph in 6th used to be 5500 rpm. Now 60 mph is 5900 rpm,according to my phone until my speedo healer gets in) so not bad at all. all around great setup