Count your teeth that are on each sprocket.....stock is 14/41. It depends a lot more on other things than just how hard you want to launch.....like your weight...the ground surface/traction your getting, the length of your swinger, the power your motor outputs, and how good you are at hitting that back brake when the front comes up too much. If your not used to it you would want to slowly change......cause if you went from stock gearing to something closer to say 12/44 your not gonna go too fast at the top speed.....but you're definitely gonna find out how good you are at wheelies....