Johnnytc3 - the main reason I am considering trying the ball diff in the rear is for the racing I do - harder spec rubber tires on medium grip asphalt, 17.5 blinky geared to the moon. With the gear diff the rear of the car can get pretty loose sometimes. A friend suggested using a ball diff instead of the gear diff in the rear after having a lot of success with it in some major races. I thought I'd give it a try. I like the spool up front, and will see how the ball diff in the rear works out.