Try 13t or 14t. 15t is fast but the batterys got warmer than I liked.4s Neuenergy 4900s hit 120 at the end of cutoff. speed runs and hard breaking due lack of runoff space.I would stay away from the losi gears due to the small set screw.I have issues with it coming loose. Been lucky enough to find it 5 time.I have yet to have one of mikes gears come loose. Cheesecake recomended this part and it is nice. king headz steering top plate
http://www.kingheads.com/product_inf...e538471f277a43 he said in another thread the carbon one breaks easily.I got it before I broke the carbon one.