Remote Control (RC) car gearing ratio information is available here:
Tighten the gear mesh so it is not fitted too tightly, or else it will make noise and cause premature wear on both the pinion and spur gear. Placing a piece of notebook paper between the pinion and spur before tightening down the motor will aid in setting the gear mesh. After the motor is secure, remove the paper and check the gear mesh. You should have minute amount of play between the gears.
Try to use a narrow strip of printer or copier paper by putting it between the pinion and spur gear while you set the tightness.