Gear Ratio Tables   Two general types of gear ratio tables are available using the links below.  The first type are basic gear ratios which simply divide the number of teeth on the crown or spur gear by the number of teeth on the pinion gear.  Use the links below to view and print basic gear ratio tables.   Basic Gear Ratio Chart     While basic gear ratios are useful, they do not take into account an important variable - the rear tire diameter.  For example, suppose 2 cars are setup with a 9 tooth pinion and 27 tooth crown gear (sometimes referred to as "9/27").  Referring to the basic gear ratio table, we see the gear ratio is 3:1.  Let's further suppose the 2 cars are identical in every respect (make, chassis, motor, etc.) with one exception.  The rear tire on the first car is 19mm in diameter while the second car's rear tire diameter is 20mm.  The "effective" gear ratio of the cars is different since the second car will travel further for each revolution of the motor than the first.  Use the links below to view and print effective gear ratio tables.   Effective Gear Ratio Chart (Crown Gears) Effective Gear Ratio Chart (Slot.it Crown Gears) Effective Gear Ratio Chart (Spur Gears) Effective Gear Ratio Chart (Slot.it Spur Gears)