How do I calculate my gear ratio?

Article #50861

How do I calculate my gear ratio?

Use the following formula:

# of teeth on the diff gear
# of teeth on the top gear
= final drive ratio
# of teeth on the spur gear
# of teeth on the pinion gear
X final drive ratio = overall ratio

Just like in a full size car, the numerically higher ratio is actually geared "lower" for more acceleration while just the opposite will permit more top speed. For example: An overall ratio of 19.72 will give you incredible acceleration, but low top speed. A 7.07 ratio would really go fast, but acceleration may be sluggish.

If you want more acceleration and less top speed, use a smaller pinion gear (fewer teeth). For more top speed, use a larger pinion gear. If you are worried that you might be under or overgeared, check the temperature of the battery pack and motor after a full run. If the batteries are extremely hot, and/or the motor is too hot to touch, your model is probably overgeared (higher ratio numerically). Try a lower gear ratio (smaller pinion gear for example). If you are not able to run your model for at least four minutes before the batteries die, then change to a lower gear ratio. This temperature test assumes that the model is close to factory stock weight and operates freely with no excessive friction, dragging, or binding.


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