[Overdriven]

The standard emaxx uses a 37/13 diff ratio, and neil is correct. If you went with the standard buggy gearing of 43/13, it would be the same as using a 15T pinion with the stock emaxx diffs. Also, your axle torque does not depend on the diff ratio. It depends on the motor and the overall final drive ratio. I don't know what motor you're using or what you're speed goals are, but I'd recommend the 43/13 buggy ratio.