I used 13t on the motor and 31t on the axle-Haven't got to test it!!!! Here's the link to that post
http://www.buggymasters.com/forum/showthread.php?t=1602 . Wish I could tell you with experience that it works!!!! I made a deal(barter agreement) for the balance of my parts several months ago but the other guy is very busy/out-of-town and I'm not on a time table-hopefully soon it'll be on the trails!