How to Calculate Gear Ratio
What is Gear Ratio?
Gear ratio is the speed reduction/increase between input and output shafts. It determines torque multiplication and shaft speeds.
Formula
Ratio = N_input / N_output = N_driven / N_driver = T_output / T_input
Step-by-Step Guide
- 1Ratio = N_input / N_output = N_driven / N_driver = T_output / T_input
- 2Spur gears: ratio = number of teeth on driven / number on driver
- 3Power is conserved: P = T × ω
Worked Examples
Input
Input 1800 rpm, output 600 rpm
Result
Gear ratio = 3:1 (3× speed reduction, 3× torque increase)
Power unchanged
Common Mistakes to Avoid
- ✕Confusing speed ratio with force multiplication
- ✕Neglecting friction losses in extended calculations
Frequently Asked Questions
Can any two gears mesh together?
No, they must have same pressure angle and pitch. Teeth must fit smoothly without interference.
How is efficiency handled?
Mechanical power loss (5-10%) converts to heat; P_out = P_in × η.
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