[RC-Monster Mike]

The optimal gearing will depend on a few things, such as your terrain, tires, diffs, cell count, etc. For racing on a track, I would stick with a 14 or 15 pinion(assuming stock diffs and stock size tires). This also assumes 12 cells. For speed runs, you could certainly gear it higher, but for general playing around in varied terrain, stick with the lower gearing for better runtimes and cooler running.