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Calculating Speed and Gear Ratios

Determining the required gear ratio or maximum speed is not always intuitive. Many factors have to be taken into account. This page is particularly useful for electric or motor-driven locomotives.

The ratios and speed required can be determined from the calculator below:-

These calculations are applicable to models with mechanical transmission systems, either petrol engine powered or electric motor powered. Allowance is also made for 2 stages of gear reduction, often required due to space limitations.

 

Gear ratio/speed Calculator
Enter either English or Metric values
below and press 'Calculate'.
[If both English and Metric values are entered for the
same parameter, only the Metric value will be used.]
     
Motor speed (max): rpm
Wheel Dia: ins or  mm
1st stage reduction: no of teeth [driving]
no of teeth [driven]
2nd stage reduction: no of teeth [driving]
no of teeth [driven]
Intermediate shaft Speed 0 rpm
Axle Speed 0 rpm
Overall reduction ratio: 0 : 1
Resultant Speed: 0 km/h
(= 0 mph)
     
Note: Simple formulas using +-*/() may be entered if desired,
not just straight plain numbers.
(for example, say 4+(3/16) may be entered for 43/16 [=4.1875])
If 2nd stage reduction is not used, use 1 for both no of teeth inputs.
Example:
Motor speed is 5000 rpm (max),
Wheel diameter is 125mm.
1st stage reduction uses sprockets of 9T and 29T,
2nd stage reduction uses gears of 10T and 29T.
Resultant maximum speed is 12.6 kmph, overall reduction ratio 9.344:1
Note the accuracy of these calculations is not necessarily exact, and figures
calculated here may vary from actual results.
Results to be used at your own risk. Calculator provided for your personal use only.

 

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