The pinion gear on your RC car is the gear that is attached to your motor, and the spur gear is the gear that the pinion drives. The spur is sometimes integrated with a slipper clutch, or with a differential in the case of a 4WD car.
When someone talks about a car's gear ratio, they are usually referring to the ratio between the spur gear and the pinion gear.
The gear ratio (aka secondary ratio) is determined by dividing the number of teeth on the spur gear by the number of teeth on the pinion gear.
gear ratio = spur / pinion
Note: the pitch of the gears does not affect the gear ratio.
Tuning with gear ratio
Larger pinion / smaller spur
- More top speed
- Less torque
- Motor/engine runs hotter
- Less efficiency / run time
Smaller pinion / larger spur
- Less top speed
- More torque
- Motor/engine runs cooler
- More efficiency / run time
Figure out which pinion gear to use on your car with our RC Gear Recommender App, and calculate your gear ratio with our Gear Ratio Calculator App.
Learn more about gear ratios: Rollout, Final Drive Ratio, and Transmission Ratio.