What year? 04-05, one down in the front would be 13T. For 06+, one down on the front is a 12T. Personally, I like to just change out the front. The rear is more involved and I don't see much difference. If you decide to change the rear, the general rule is that a 3 tooth difference is about equal to changing 1 tooth on the front. To go "down" in gearing by changing the rear sprocket, you would increase the number of teeth. So it is opposite the front.