How to Calculate Gear Ratios for Slot Cars

Slot cars have been running around tracks since the 1960s, entertaining generations of participants in an environment every bit as exciting and as challenging as those at LeMans, France or Daytona International Speedway. Originally, the cars were powered by electric motors but today, gasoline engines propel these machines to speeds unheard of in the early days of the sport. One factor in their speed is the gear ratio the racers use--like the gear ratio in an automobile, it represents how many times the engine must turn to make the wheels turn one time.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Slot car

1. Remove the body of the slot car and any protective covering over the motor and the drive axle.

2. Count the number of teeth on the pinion gear attached to the shaft of the motor.

3. Count the number of teeth on the crown gear attached to the drive axle.

4. Divide the larger number (the crown gear) by the smaller (the pinon gear): if the pinion gear has 12 teeth and the ring gear 28, divide 28 by 12. The answer, 2.33, is the number of times the pinion must turn to make the crown gear (and the drive axle) turn once. Therefore, the gear ratio is 2.33 to 1 (the number for the pinion is stated first). If the gearing is reversed, that is, the pinion gear has 28 teeth whereas the crown gear has 12, the process is the same, divide larger by smaller, but the ratio is stated as the number of times the pinion turns, followed by the number of times the crown gear (and the drive axle) turns: 1 to 2.33.

Tips & Warnings

• Short gear ratios, where the number of teeth on the ring gear of the drive axle is 4 or 5 times the number of teeth on the pinion gear, make the car accelerate faster, but limit its top speed: good for accelerating out of a turn, but bad for long straightaways. Long gear ratios mean more top speed, but slower acceleration.

References

• SlotCar Corner.com: Gear Ratio Tables

Resources

• Slot Car Academy